diff --git a/2 b/2
new file mode 100644
index 0000000000..b0702f970a
--- /dev/null
+++ b/2
@@ -0,0 +1,804 @@
+#[macro_use]
+extern crate pretty_assertions;
+#[macro_use]
+extern crate indoc;
+
+extern crate bumpalo;
+extern crate inkwell;
+extern crate libc;
+extern crate roc_gen;
+
+#[macro_use]
+mod helpers;
+
+#[cfg(test)]
+mod gen_tags {
+    use crate::helpers::{can_expr, infer_expr, uniq_expr, CanExprOut};
+    use bumpalo::Bump;
+    use inkwell::context::Context;
+    use inkwell::execution_engine::JitFunction;
+    use inkwell::passes::PassManager;
+    use inkwell::types::BasicType;
+    use inkwell::OptimizationLevel;
+    use roc_collections::all::ImMap;
+    use roc_gen::llvm::build::{build_proc, build_proc_header};
+    use roc_gen::llvm::convert::basic_type_from_layout;
+    use roc_mono::expr::{Expr, Procs};
+    use roc_mono::layout::Layout;
+    use roc_types::subs::Subs;
+
+    use inkwell::targets::{
+        CodeModel, FileType, InitializationConfig, RelocMode, Target, TargetMachine, TargetTriple,
+    };
+    use std::path::Path;
+
+    #[test]
+    fn applied_tag_nothing() {
+        assert_evals_to!(
+            indoc!(
+                r#"
+                Maybe a : [ Just a, Nothing ]
+
+                x : Maybe Int
+                x = Nothing
+
+                0x1
+                "#
+            ),
+            1,
+            i64
+        );
+    }
+
+    #[test]
+    fn applied_tag_just() {
+        assert_evals_to!(
+            indoc!(
+                r#"
+                Maybe a : [ Just a, Nothing ]
+
+                y : Maybe Int
+                y = Just 0x4
+
+                0x1
+                "#
+            ),
+            1,
+            i64
+        );
+    }
+
+    #[test]
+    fn applied_tag_just_unit() {
+        assert_evals_to!(
+            indoc!(
+                r#"
+                Fruit : [ Orange, Apple, Banana ]
+                Maybe a : [ Just a, Nothing ]
+
+                orange : Fruit
+                orange = Orange
+
+                y : Maybe Fruit
+                y = Just orange
+
+                0x1
+                "#
+            ),
+            1,
+            i64
+        );
+    }
+
+    // #[test]
+    // fn raw_result() {
+    //     assert_evals_to!(
+    //         indoc!(
+    //             r#"
+    //             x : Result Int Int
+    //             x = Err 41
+
+    //             x
+    //             "#
+    //         ),
+    //         0,
+    //         i8
+    //     );
+    // }
+
+    #[test]
+    fn true_is_true() {
+        assert_evals_to!(
+            indoc!(
+                r#"
+                   bool : [True, False]
+                   bool = True
+
+                   bool
+                "#
+            ),
+            true,
+            bool
+        );
+    }
+
+    #[test]
+    fn false_is_false() {
+        assert_evals_to!(
+            indoc!(
+                r#"
+                   bool : [True, False]
+                   bool = False
+
+                   bool
+                "#
+            ),
+            false,
+            bool
+        );
+    }
+
+    #[test]
+    fn basic_enum() {
+        assert_evals_to!(
+            indoc!(
+                r#"
+                Fruit : [ Apple, Orange, Banana ]
+
+                apple : Fruit
+                apple = Apple
+
+                orange : Fruit
+                orange = Orange
+
+                apple == orange
+                "#
+            ),
+            false,
+            bool
+        );
+    }
+
+    //    #[test]
+    //    fn linked_list_empty() {
+    //        assert_evals_to!(
+    //            indoc!(
+    //                r#"
+    //                LinkedList a : [ Cons a (LinkedList a), Nil ]
+    //
+    //                empty : LinkedList Int
+    //                empty = Nil
+    //
+    //                1
+    //                "#
+    //            ),
+    //            1,
+    //            i64
+    //        );
+    //    }
+    //
+    //    #[test]
+    //    fn linked_list_singleton() {
+    //        assert_evals_to!(
+    //            indoc!(
+    //                r#"
+    //                LinkedList a : [ Cons a (LinkedList a), Nil ]
+    //
+    //                singleton : LinkedList Int
+    //                singleton = Cons 0x1 Nil
+    //
+    //                1
+    //                "#
+    //            ),
+    //            1,
+    //            i64
+    //        );
+    //    }
+    //
+    //    #[test]
+    //    fn linked_list_is_empty() {
+    //        assert_evals_to!(
+    //            indoc!(
+    //                r#"
+    //                LinkedList a : [ Cons a (LinkedList a), Nil ]
+    //
+    //                isEmpty : LinkedList a -> Bool
+    //                isEmpty = \list ->
+    //                    when list is
+    //                        Nil -> True
+    //                        Cons _ _ -> False
+    //
+    //                isEmpty (Cons 4 Nil)
+    //                "#
+    //            ),
+    //            false,
+    //            bool
+    //        );
+    //    }
+
+    #[test]
+    fn even_odd() {
+        assert_evals_to!(
+            indoc!(
+                r#"
+                even = \n ->
+                    when n is
+                        0 -> True
+                        1 -> False
+                        _ -> odd (n - 1)
+
+                odd = \n ->
+                    when n is
+                        0 -> False
+                        1 -> True
+                        _ -> even (n - 1)
+
+                odd 5 && even 42
+                "#
+            ),
+            true,
+            bool
+        );
+    }
+
+    #[test]
+    fn gen_literal_true() {
+        assert_evals_to!(
+            indoc!(
+                r#"
+                if True then -1 else 1
+                "#
+            ),
+            -1,
+            i64
+        );
+    }
+
+    #[test]
+    fn gen_if_float() {
+        assert_evals_to!(
+            indoc!(
+                r#"
+                if True then -1.0 else 1.0
+                "#
+            ),
+            -1.0,
+            f64
+        );
+    }
+    #[test]
+    fn when_on_nothing() {
+        assert_evals_to!(
+            indoc!(
+                r#"
+                x : [ Nothing, Just Int ]
+                x = Nothing
+
+                when x is
+                    Nothing -> 0x2
+                    Just _ -> 0x1
+                "#
+            ),
+            2,
+            i64
+        );
+    }
+
+    #[test]
+    fn when_on_just() {
+        assert_evals_to!(
+            indoc!(
+                r#"
+                x : [ Nothing, Just Int ]
+                x = Just 41
+
+                when x is
+                    Just v -> v + 0x1
+                    Nothing -> 0x1
+                "#
+            ),
+            42,
+            i64
+        );
+    }
+
+    #[test]
+    fn when_on_result() {
+        assert_evals_to!(
+            indoc!(
+                r#"
+                x : Result Int Int
+                x = Err 41
+
+                when x is
+                    Err v ->  v + 1
+                    Ok _ -> 1
+                "#
+            ),
+            42,
+            i64
+        );
+    }
+
+    #[test]
+    fn when_on_these() {
+        assert_evals_to!(
+            indoc!(
+                r#"
+                These a b : [ This a, That b, These a b ]
+
+                x : These Int Int
+                x = These 0x3 0x2
+
+                when x is
+                    These a b -> a + b
+                    That v -> 8
+                    This v -> v
+                "#
+            ),
+            5,
+            i64
+        );
+    }
+
+    #[test]
+    fn match_on_two_values() {
+        // this will produce a Chain internally
+        assert_evals_to!(
+            indoc!(
+                r#"
+                when Pair 2 3 is
+                    Pair 4 3 -> 9
+                    Pair a b -> a + b
+                "#
+            ),
+            5,
+            i64
+        );
+    }
+
+    #[test]
+    fn pair_with_guard_pattern() {
+        assert_evals_to!(
+            indoc!(
+                r#"
+                when Pair 2 3 is
+                    Pair 4 _ -> 1
+                    Pair 3 _ -> 2
+                    Pair a b -> a + b
+                "#
+            ),
+            5,
+            i64
+        );
+    }
+
+    #[test]
+    fn result_with_guard_pattern() {
+        // This test revealed an issue with hashing Test values
+        assert_evals_to!(
+            indoc!(
+                r#"
+            x : Result Int Int
+            x = Ok 2
+
+            when x is
+                Ok 3 -> 1
+                Ok _ -> 2
+                Err _ -> 3
+            "#
+            ),
+            2,
+            i64
+        );
+    }
+
+    #[test]
+    fn maybe_is_just() {
+        assert_evals_to!(
+            indoc!(
+                r#"
+                Maybe a : [ Just a, Nothing ]
+
+                isJust : Maybe a -> Bool
+                isJust = \list ->
+                    when list is
+                        Nothing -> False
+                        Just _ -> True
+
+                isJust (Just 42)
+                "#
+            ),
+            true,
+            bool
+        );
+    }
+
+    #[test]
+    fn nested_pattern_match() {
+        assert_evals_to!(
+            indoc!(
+                r#"
+                Maybe a : [ Nothing, Just a ]
+
+                x : Maybe (Maybe Int)
+                x = Just (Just 41)
+
+                when x is
+                    Just (Just v) -> v + 0x1
+                    _ -> 0x1
+                "#
+            ),
+            42,
+            i64
+        );
+    }
+    #[test]
+    fn if_guard_pattern_false() {
+        assert_evals_to!(
+            indoc!(
+                r#"
+                when 2 is
+                    2 if False -> 0
+                    _ -> 42
+                "#
+            ),
+            42,
+            i64
+        );
+    }
+
+    #[test]
+    fn if_guard_pattern_true() {
+        assert_evals_to!(
+            indoc!(
+                r#"
+                when 2 is
+                    2 if True -> 42
+                    _ -> 0
+                "#
+            ),
+            42,
+            i64
+        );
+    }
+
+    #[test]
+    fn if_guard_exhaustiveness() {
+        assert_evals_to!(
+            indoc!(
+                r#"
+                when 2 is
+                    _ if False -> 0
+                    _ -> 42
+                "#
+            ),
+            42,
+            i64
+        );
+    }
+
+    #[test]
+    fn when_on_enum() {
+        assert_evals_to!(
+            indoc!(
+                r#"
+                Fruit : [ Apple, Orange, Banana ]
+
+                apple : Fruit
+                apple = Apple
+
+                when apple is
+                    Apple -> 1
+                    Banana -> 2
+                    Orange -> 3
+                "#
+            ),
+            1,
+            i64
+        );
+    }
+
+    #[test]
+    fn pattern_matching_unit() {
+        assert_evals_to!(
+            indoc!(
+                r#"
+                Unit : [ Unit ]
+
+                f : Unit -> Int
+                f = \Unit -> 42
+
+                f Unit
+                "#
+            ),
+            42,
+            i64
+        );
+
+        assert_evals_to!(
+            indoc!(
+                r#"
+                Unit : [ Unit ]
+
+                x : Unit
+                x = Unit
+
+                when x is
+                    Unit -> 42
+                "#
+            ),
+            42,
+            i64
+        );
+
+        assert_evals_to!(
+            indoc!(
+                r#"
+                f : {} -> Int
+                f = \{} -> 42
+
+                f {}
+                "#
+            ),
+            42,
+            i64
+        );
+
+        assert_evals_to!(
+            indoc!(
+                r#"
+                when {} is
+                    {} -> 42
+                "#
+            ),
+            42,
+            i64
+        );
+    }
+
+    #[test]
+    fn one_element_tag() {
+        assert_evals_to!(
+            indoc!(
+                r#"
+                x : [ Pair Int ]
+                x = Pair 2
+
+                0x3
+                "#
+            ),
+            3,
+            i64
+        );
+    }
+
+    #[test]
+    fn nested_tag_union() {
+        assert_evals_to!(
+            indoc!(
+                r#"
+                Maybe a : [ Nothing, Just a ]
+
+                x : Maybe (Maybe a)
+                x = Just (Just 41)
+
+                5
+                "#
+            ),
+            5,
+            i64
+        );
+    }
+    #[test]
+    fn unit_type() {
+        assert_evals_to!(
+            indoc!(
+                r#"
+                Unit : [ Unit ]
+
+                v : Unit
+                v = Unit
+
+                1
+                "#
+            ),
+            1,
+            i64
+        );
+    }
+
+    #[test]
+    fn nested_record_load() {
+        assert_evals_to!(
+            indoc!(
+                r#"
+                Maybe a : [ Nothing, Just a ]
+
+                x = { a : { b : 0x5 } }
+
+                y = x.a
+
+                y.b
+                "#
+            ),
+            5,
+            i64
+        );
+    }
+
+    #[test]
+    fn test_emit() {
+        let src = "42";
+
+        // Build the expr
+        let arena = Bump::new();
+        let (loc_expr, _output, _problems, subs, var, constraint, home, interns) = uniq_expr(src);
+
+        let mut unify_problems = Vec::new();
+        let (content, mut subs) = infer_expr(subs, &mut unify_problems, &constraint, var);
+
+        let context = Context::create();
+        let module = context.create_module("app");
+        let builder = context.create_builder();
+        let fpm = PassManager::create(&module);
+
+        roc_gen::llvm::build::add_passes(&fpm);
+
+        fpm.initialize();
+
+        // Compute main_fn_type before moving subs to Env
+        let layout = Layout::from_content(&arena, content, &subs, crate::helpers::eval::POINTER_SIZE)
+    .unwrap_or_else(|err| panic!("Code gen error in test: could not convert to layout. Err was {:?} and Subs were {:?}", err, subs));
+
+        let execution_engine =
+            module
+            .create_jit_execution_engine(OptimizationLevel::None)
+            .expect("Error creating JIT execution engine for test");
+
+        let ptr_bytes = execution_engine.get_target_data().get_pointer_byte_size(None);
+        let main_fn_type = basic_type_from_layout(&arena, &context, &layout, ptr_bytes)
+            .fn_type(&[], false);
+        let main_fn_name = "$Test.main";
+
+        // Compile and add all the Procs before adding main
+        let mut env = roc_gen::llvm::build::Env {
+            arena: &arena,
+            builder: &builder,
+            context: &context,
+            interns,
+            module: arena.alloc(module),
+            ptr_bytes
+        };
+        let mut procs = Procs::default();
+        let mut ident_ids = env.interns.all_ident_ids.remove(&home).unwrap();
+
+        // Populate Procs and get the low-level Expr from the canonical Expr
+        let main_body = Expr::new(&arena, &mut subs, loc_expr.value, &mut procs, home, &mut ident_ids, $crate::helpers::eval::POINTER_SIZE);
+
+        // Put this module's ident_ids back in the interns, so we can use them in Env.
+        env.interns.all_ident_ids.insert(home, ident_ids);
+
+        let mut headers = Vec::with_capacity(procs.len());
+
+        // Add all the Proc headers to the module.
+        // We have to do this in a separate pass first,
+        // because their bodies may reference each other.
+        for (symbol, opt_proc) in procs.as_map().into_iter() {
+            if let Some(proc) = opt_proc {
+                let (fn_val, arg_basic_types) = build_proc_header(&env, symbol, &proc);
+
+                headers.push((proc, fn_val, arg_basic_types));
+            }
+        }
+
+        // Build each proc using its header info.
+        for (proc, fn_val, arg_basic_types) in headers {
+            // NOTE: This is here to be uncommented in case verification fails.
+            // (This approach means we don't have to defensively clone name here.)
+            //
+            // println!("\n\nBuilding and then verifying function {}\n\n", name);
+            build_proc(&env, proc, &procs, fn_val, arg_basic_types);
+
+            if fn_val.verify(true) {
+                fpm.run_on(&fn_val);
+            } else {
+                // NOTE: If this fails, uncomment the above println to debug.
+                panic!("Non-main function failed LLVM verification. Uncomment the above println to debug!");
+            }
+        }
+
+        // Add main to the module.
+        let main_fn = env.module.add_function(main_fn_name, main_fn_type, None);
+
+        main_fn.set_call_conventions($crate::helpers::eval::MAIN_CALLING_CONVENTION);
+
+        // Add main's body
+        let basic_block = context.append_basic_block(main_fn, "entry");
+
+        builder.position_at_end(basic_block);
+
+        let ret = roc_gen::llvm::build::build_expr(
+            &env,
+            &ImMap::default(),
+            main_fn,
+            &main_body,
+            &mut Procs::default(),
+        );
+
+        builder.build_return(Some(&ret));
+
+        // Uncomment this to see the module's un-optimized LLVM instruction output:
+        // env.module.print_to_stderr();
+
+        if main_fn.verify(true) {
+            fpm.run_on(&main_fn);
+        } else {
+            panic!("Function {} failed LLVM verification.", main_fn_name);
+        }
+
+        // Verify the module
+        if let Err(errors) = env.module.verify() {
+            panic!("Errors defining module: {:?}", errors);
+        }
+
+        // Uncomment this to see the module's optimized LLVM instruction output:
+        // env.module.print_to_stderr();
+
+        // Emit
+        Target::initialize_x86(&InitializationConfig::default());
+
+        let opt = OptimizationLevel::Default;
+        let reloc = RelocMode::Default;
+        let model = CodeModel::Default;
+        let target = Target::from_name("x86-64").unwrap();
+        let target_machine = target.create_target_machine(
+            &TargetTriple::create("x86_64-pc-linux-gnu"),
+            "x86-64",
+            "+avx2",
+            opt,
+            reloc,
+            model
+        )
+        .unwrap();
+
+        let buffer = target_machine.write_to_memory_buffer(&module, FileType::Assembly).unwrap();
+
+        let buffer_str = std::str::from_utf8(buffer).unwrap();
+
+    }
+
+    #[test]
+    fn test_emit_old() {
+        Target::initialize_x86(&InitializationConfig::default());
+
+        let opt = OptimizationLevel::Default;
+        let reloc = RelocMode::Default;
+        let model = CodeModel::Default;
+        let path = Path::new("./test.asm");
+        let target = Target::from_name("x86-64").unwrap();
+        let target_machine = target
+            .create_target_machine(
+                &TargetTriple::create("x86_64-pc-linux-gnu"),
+                "x86-64",
+                "+avx2",
+                opt,
+                reloc,
+                model,
+            )
+            .unwrap();
+
+        let context = Context::create();
+        let module = context.create_module("my_module");
+        let void_type = context.void_type();
+        let fn_type = void_type.fn_type(&[], false);
+
+        module.add_function("my_fn", fn_type, None);
+
+        target_machine
+            .write_to_file(&module, FileType::Assembly, &path)
+            .expect("writing to file succeeded");
+
+        panic!("TODO remove this test");
+    }
+}
diff --git a/BUILDING_FROM_SOURCE.md b/BUILDING_FROM_SOURCE.md
index a13d3b5ecf..172a845752 100644
--- a/BUILDING_FROM_SOURCE.md
+++ b/BUILDING_FROM_SOURCE.md
@@ -22,3 +22,21 @@ Caused by:
 ```
 
 This seems to be caused by cargo being out of date (even if it's freshly installed), and can be fixed with `cargo update`. 
+
+## Use LLD for the linker
+
+Using [`lld` for Rust's linker](https://github.com/rust-lang/rust/issues/39915#issuecomment-538049306)
+makes build times a lot faster, and I highly recommend it.
+
+Create `~/.config/cargo` and add this to it:
+
+```
+[build]
+rustflags = ["-C", "link-arg=-fuse-ld=lld"]
+```
+
+Then install `lld` version 9 (e.g. with `$ sudo apt-get install lld-9`)
+and add make sure there's a `ld.lld` executable on your `PATH` which
+is symlinked to `lld-9`.
+
+That's it! Enjoy the faster builds.
diff --git a/Cargo.lock b/Cargo.lock
index d8c1dca795..141806b2a6 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -526,6 +526,32 @@ version = "0.6.17"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7fe5bd57d1d7414c6b5ed48563a2c855d995ff777729dcd91c369ec7fea395ae"
 
+[[package]]
+name = "roc-cli"
+version = "0.1.0"
+dependencies = [
+ "bumpalo",
+ "im",
+ "im-rc",
+ "inkwell",
+ "inlinable_string",
+ "roc_builtins",
+ "roc_can",
+ "roc_collections",
+ "roc_constrain",
+ "roc_gen",
+ "roc_module",
+ "roc_mono",
+ "roc_parse",
+ "roc_problem",
+ "roc_region",
+ "roc_solve",
+ "roc_types",
+ "roc_unify",
+ "roc_uniq",
+ "target-lexicon",
+]
+
 [[package]]
 name = "roc_builtins"
 version = "0.1.0"
@@ -642,6 +668,7 @@ dependencies = [
  "roc_types",
  "roc_unify",
  "roc_uniq",
+ "target-lexicon",
  "tokio",
 ]
 
@@ -904,6 +931,12 @@ dependencies = [
  "unicode-xid 0.2.0",
 ]
 
+[[package]]
+name = "target-lexicon"
+version = "0.10.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ab0e7238dcc7b40a7be719a25365910f6807bd864f4cce6b2e6b873658e2b19d"
+
 [[package]]
 name = "thread_local"
 version = "1.0.1"
diff --git a/Cargo.toml b/Cargo.toml
index 9aa94be014..9a713fbff2 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -19,5 +19,7 @@ members = [
     "compiler/load",
     "compiler/gen",
     "vendor/ena",
-    "vendor/pathfinding"
+    "vendor/pathfinding",
+    "cli"
 ]
+
diff --git a/a.out b/a.out
new file mode 100755
index 0000000000..42cca021e2
Binary files /dev/null and b/a.out differ
diff --git a/cli/Cargo.toml b/cli/Cargo.toml
index 30c7aadbba..5b471cfb90 100644
--- a/cli/Cargo.toml
+++ b/cli/Cargo.toml
@@ -8,6 +8,50 @@ keywords = ["roc", "gui"]
 edition = "2018"
 description = "A CLI for Roc"
 license = "Apache-2.0"
+default-run = "roc"
+
+[[bin]]
+name = "roc"
+path = "src/main.rs"
+test = false
+bench = false
+
 
 [dependencies]
-roc = { path = "../", version = "0.1.0" }
+roc_collections = { path = "../compiler/collections" }
+roc_can = { path = "../compiler/can" }
+roc_parse = { path = "../compiler/parse" }
+roc_region = { path = "../compiler/region" }
+roc_module = { path = "../compiler/module" }
+roc_problem = { path = "../compiler/problem" }
+roc_types = { path = "../compiler/types" }
+roc_builtins = { path = "../compiler/builtins" }
+roc_constrain = { path = "../compiler/constrain" }
+roc_uniq = { path = "../compiler/uniq" }
+roc_unify = { path = "../compiler/unify" }
+roc_solve = { path = "../compiler/solve" }
+roc_mono = { path = "../compiler/mono" }
+roc_gen = { path = "../compiler/gen", version = "0.1.0" }
+im    = "14" # im and im-rc should always have the same version!
+im-rc = "14" # im and im-rc should always have the same version!
+bumpalo = { version = "3.2", features = ["collections"] }
+inlinable_string = "0.1.0"
+# NOTE: rtfeldman/inkwell is a fork of TheDan64/inkwell which does not change anything.
+#
+# The reason for this fork is that the way Inkwell is designed, you have to use
+# a particular branch (e.g. "llvm8-0") in Cargo.toml. That would be fine, except that
+# breaking changes get pushed directly to that branch, which breaks our build
+# without warning.
+#
+# We tried referencing a specific rev on TheDan64/inkwell directly (instead of branch),
+# but although that worked locally, it did not work on GitHub Actions. (After a few
+# hours of investigation, gave up trying to figure out why.) So this is the workaround:
+# having an immutable tag on the rtfeldman/inkwell fork which points to
+# a particular "release" of Inkwell.
+#
+# When we want to update Inkwell, we can sync up rtfeldman/inkwell to the latest
+# commit of TheDan64/inkwell, push a new tag which points to the latest commit,
+# change the tag value in this Cargo.toml to point to that tag, and `cargo update`.
+# This way, GitHub Actions works and nobody's builds get broken.
+inkwell = { git = "https://github.com/rtfeldman/inkwell", tag = "llvm8-0.release2" }
+target-lexicon = "0.10"
diff --git a/cli/src/helpers.rs b/cli/src/helpers.rs
new file mode 100644
index 0000000000..9ed8b4dc12
--- /dev/null
+++ b/cli/src/helpers.rs
@@ -0,0 +1,396 @@
+use bumpalo::Bump;
+use roc_builtins::unique::uniq_stdlib;
+use roc_can::constraint::Constraint;
+use roc_can::env::Env;
+use roc_can::expected::Expected;
+use roc_can::expr::{canonicalize_expr, Expr, Output};
+use roc_can::operator;
+use roc_can::scope::Scope;
+use roc_collections::all::{ImMap, ImSet, MutMap, SendMap, SendSet};
+use roc_constrain::expr::constrain_expr;
+use roc_constrain::module::{constrain_imported_values, load_builtin_aliases, Import};
+use roc_module::ident::Ident;
+use roc_module::symbol::{IdentIds, Interns, ModuleId, ModuleIds, Symbol};
+use roc_parse::ast::{self, Attempting};
+use roc_parse::blankspace::space0_before;
+use roc_parse::parser::{loc, Fail, Parser, State};
+use roc_problem::can::Problem;
+use roc_region::all::{Located, Region};
+use roc_solve::solve;
+use roc_types::subs::{Content, Subs, VarStore, Variable};
+use roc_types::types::Type;
+use std::hash::Hash;
+
+pub fn test_home() -> ModuleId {
+    ModuleIds::default().get_or_insert(&"Test".into())
+}
+
+pub fn infer_expr(
+    subs: Subs,
+    problems: &mut Vec<roc_types::types::Problem>,
+    constraint: &Constraint,
+    expr_var: Variable,
+) -> (Content, Subs) {
+    let env = solve::Env {
+        aliases: MutMap::default(),
+        vars_by_symbol: SendMap::default(),
+    };
+    let (solved, _) = solve::run(&env, problems, subs, constraint);
+
+    let content = solved.inner().get_without_compacting(expr_var).content;
+
+    (content, solved.into_inner())
+}
+
+pub fn parse_with<'a>(arena: &'a Bump, input: &'a str) -> Result<ast::Expr<'a>, Fail> {
+    parse_loc_with(arena, input).map(|loc_expr| loc_expr.value)
+}
+
+pub fn parse_loc_with<'a>(arena: &'a Bump, input: &'a str) -> Result<Located<ast::Expr<'a>>, Fail> {
+    let state = State::new(&input, Attempting::Module);
+    let parser = space0_before(loc(roc_parse::expr::expr(0)), 0);
+    let answer = parser.parse(&arena, state);
+
+    answer
+        .map(|(loc_expr, _)| loc_expr)
+        .map_err(|(fail, _)| fail)
+}
+
+pub fn can_expr(expr_str: &str) -> CanExprOut {
+    can_expr_with(&Bump::new(), test_home(), expr_str)
+}
+
+pub fn uniq_expr(
+    expr_str: &str,
+) -> (
+    Located<Expr>,
+    Output,
+    Vec<Problem>,
+    Subs,
+    Variable,
+    Constraint,
+    ModuleId,
+    Interns,
+) {
+    let declared_idents: &ImMap<Ident, (Symbol, Region)> = &ImMap::default();
+
+    uniq_expr_with(&Bump::new(), expr_str, declared_idents)
+}
+
+pub fn uniq_expr_with(
+    arena: &Bump,
+    expr_str: &str,
+    declared_idents: &ImMap<Ident, (Symbol, Region)>,
+) -> (
+    Located<Expr>,
+    Output,
+    Vec<Problem>,
+    Subs,
+    Variable,
+    Constraint,
+    ModuleId,
+    Interns,
+) {
+    let home = test_home();
+    let CanExprOut {
+        loc_expr,
+        output,
+        problems,
+        var_store: old_var_store,
+        var,
+        interns,
+        ..
+    } = can_expr_with(arena, home, expr_str);
+
+    // double check
+    let var_store = VarStore::new(old_var_store.fresh());
+
+    let expected2 = Expected::NoExpectation(Type::Variable(var));
+    let constraint = roc_constrain::uniq::constrain_declaration(
+        home,
+        &var_store,
+        Region::zero(),
+        &loc_expr,
+        declared_idents,
+        expected2,
+    );
+
+    let stdlib = uniq_stdlib();
+
+    let types = stdlib.types;
+    let imports: Vec<_> = types
+        .iter()
+        .map(|(symbol, (solved_type, region))| Import {
+            loc_symbol: Located::at(*region, *symbol),
+            solved_type,
+        })
+        .collect();
+
+    // load builtin values
+
+    // TODO what to do with those rigids?
+    let (_introduced_rigids, constraint) =
+        constrain_imported_values(imports, constraint, &var_store);
+
+    // load builtin types
+    let mut constraint = load_builtin_aliases(&stdlib.aliases, constraint, &var_store);
+
+    constraint.instantiate_aliases(&var_store);
+
+    let subs2 = Subs::new(var_store.into());
+
+    (
+        loc_expr, output, problems, subs2, var, constraint, home, interns,
+    )
+}
+
+pub struct CanExprOut {
+    pub loc_expr: Located<Expr>,
+    pub output: Output,
+    pub problems: Vec<Problem>,
+    pub home: ModuleId,
+    pub interns: Interns,
+    pub var_store: VarStore,
+    pub var: Variable,
+    pub constraint: Constraint,
+}
+
+pub fn can_expr_with(arena: &Bump, home: ModuleId, expr_str: &str) -> CanExprOut {
+    let loc_expr = parse_loc_with(&arena, expr_str).unwrap_or_else(|e| {
+        panic!(
+            "can_expr_with() got a parse error when attempting to canonicalize:\n\n{:?} {:?}",
+            expr_str, e
+        )
+    });
+
+    let var_store = VarStore::default();
+    let var = var_store.fresh();
+    let expected = Expected::NoExpectation(Type::Variable(var));
+    let module_ids = ModuleIds::default();
+
+    // Desugar operators (convert them to Apply calls, taking into account
+    // operator precedence and associativity rules), before doing other canonicalization.
+    //
+    // If we did this *during* canonicalization, then each time we
+    // visited a BinOp node we'd recursively try to apply this to each of its nested
+    // operators, and then again on *their* nested operators, ultimately applying the
+    // rules multiple times unnecessarily.
+    let loc_expr = operator::desugar_expr(arena, &loc_expr);
+
+    let mut scope = Scope::new(home);
+    let dep_idents = IdentIds::exposed_builtins(0);
+    let mut env = Env::new(home, dep_idents, &module_ids, IdentIds::default());
+    let (loc_expr, output) = canonicalize_expr(
+        &mut env,
+        &var_store,
+        &mut scope,
+        Region::zero(),
+        &loc_expr.value,
+    );
+
+    let constraint = constrain_expr(
+        &roc_constrain::expr::Env {
+            rigids: ImMap::default(),
+            home,
+        },
+        loc_expr.region,
+        &loc_expr.value,
+        expected,
+    );
+
+    let types = roc_builtins::std::types();
+
+    let imports: Vec<_> = types
+        .iter()
+        .map(|(symbol, (solved_type, region))| Import {
+            loc_symbol: Located::at(*region, *symbol),
+            solved_type,
+        })
+        .collect();
+
+    //load builtin values
+    let (_introduced_rigids, constraint) =
+        constrain_imported_values(imports, constraint, &var_store);
+
+    // TODO determine what to do with those rigids
+    //    for var in introduced_rigids {
+    //        output.ftv.insert(var, format!("internal_{:?}", var).into());
+    //    }
+
+    //load builtin types
+    let mut constraint =
+        load_builtin_aliases(&roc_builtins::std::aliases(), constraint, &var_store);
+
+    constraint.instantiate_aliases(&var_store);
+
+    let mut all_ident_ids = MutMap::default();
+
+    // When pretty printing types, we may need the exposed builtins,
+    // so include them in the Interns we'll ultimately return.
+    for (module_id, ident_ids) in IdentIds::exposed_builtins(0) {
+        all_ident_ids.insert(module_id, ident_ids);
+    }
+
+    all_ident_ids.insert(home, env.ident_ids);
+
+    let interns = Interns {
+        module_ids: env.module_ids.clone(),
+        all_ident_ids,
+    };
+
+    CanExprOut {
+        loc_expr,
+        output,
+        problems: env.problems,
+        home: env.home,
+        var_store,
+        interns,
+        var,
+        constraint,
+    }
+}
+
+pub fn mut_map_from_pairs<K, V, I>(pairs: I) -> MutMap<K, V>
+where
+    I: IntoIterator<Item = (K, V)>,
+    K: Hash + Eq,
+{
+    let mut answer = MutMap::default();
+
+    for (key, value) in pairs {
+        answer.insert(key, value);
+    }
+
+    answer
+}
+
+pub fn im_map_from_pairs<K, V, I>(pairs: I) -> ImMap<K, V>
+where
+    I: IntoIterator<Item = (K, V)>,
+    K: Hash + Eq + Clone,
+    V: Clone,
+{
+    let mut answer = ImMap::default();
+
+    for (key, value) in pairs {
+        answer.insert(key, value);
+    }
+
+    answer
+}
+
+pub fn send_set_from<V, I>(elems: I) -> SendSet<V>
+where
+    I: IntoIterator<Item = V>,
+    V: Hash + Eq + Clone,
+{
+    let mut answer = SendSet::default();
+
+    for elem in elems {
+        answer.insert(elem);
+    }
+
+    answer
+}
+
+// Check constraints
+//
+// Keep track of the used (in types or expectations) variables, and the declared variables (in
+// flex_vars or rigid_vars fields of LetConstraint. These roc_collections should match: no duplicates
+// and no variables that are used but not declared are allowed.
+//
+// There is one exception: the initial variable (that stores the type of the whole expression) is
+// never declared, but is used.
+pub fn assert_correct_variable_usage(constraint: &Constraint) {
+    // variables declared in constraint (flex_vars or rigid_vars)
+    // and variables actually used in constraints
+    let (declared, used) = variable_usage(constraint);
+
+    let used: ImSet<Variable> = used.into();
+    let mut decl: ImSet<Variable> = declared.rigid_vars.clone().into();
+
+    for var in declared.flex_vars.clone() {
+        decl.insert(var);
+    }
+
+    let diff = used.clone().relative_complement(decl);
+
+    // NOTE: this checks whether we're using variables that are not declared. For recursive type
+    // definitions,  their rigid types are declared twice, which is correct!
+    if !diff.is_empty() {
+        println!("VARIABLE USAGE PROBLEM");
+
+        println!("used: {:?}", &used);
+        println!("rigids: {:?}", &declared.rigid_vars);
+        println!("flexs: {:?}", &declared.flex_vars);
+
+        println!("difference: {:?}", &diff);
+
+        panic!("variable usage problem (see stdout for details)");
+    }
+}
+
+#[derive(Default)]
+pub struct SeenVariables {
+    pub rigid_vars: Vec<Variable>,
+    pub flex_vars: Vec<Variable>,
+}
+
+pub fn variable_usage(con: &Constraint) -> (SeenVariables, Vec<Variable>) {
+    let mut declared = SeenVariables::default();
+    let mut used = ImSet::default();
+    variable_usage_help(con, &mut declared, &mut used);
+
+    used.remove(unsafe { &Variable::unsafe_test_debug_variable(1) });
+
+    let mut used_vec: Vec<Variable> = used.into_iter().collect();
+    used_vec.sort();
+
+    declared.rigid_vars.sort();
+    declared.flex_vars.sort();
+
+    (declared, used_vec)
+}
+
+fn variable_usage_help(con: &Constraint, declared: &mut SeenVariables, used: &mut ImSet<Variable>) {
+    use Constraint::*;
+
+    match con {
+        True | SaveTheEnvironment => (),
+        Eq(tipe, expectation, _) => {
+            for v in tipe.variables() {
+                used.insert(v);
+            }
+
+            for v in expectation.get_type_ref().variables() {
+                used.insert(v);
+            }
+        }
+        Lookup(_, expectation, _) => {
+            for v in expectation.get_type_ref().variables() {
+                used.insert(v);
+            }
+        }
+        Pattern(_, _, tipe, pexpectation) => {
+            for v in tipe.variables() {
+                used.insert(v);
+            }
+
+            for v in pexpectation.get_type_ref().variables() {
+                used.insert(v);
+            }
+        }
+        Let(letcon) => {
+            declared.rigid_vars.extend(letcon.rigid_vars.clone());
+            declared.flex_vars.extend(letcon.flex_vars.clone());
+
+            variable_usage_help(&letcon.defs_constraint, declared, used);
+            variable_usage_help(&letcon.ret_constraint, declared, used);
+        }
+        And(constraints) => {
+            for sub in constraints {
+                variable_usage_help(sub, declared, used);
+            }
+        }
+    }
+}
diff --git a/cli/src/main.rs b/cli/src/main.rs
index 1046a9c40a..a0f44b1520 100644
--- a/cli/src/main.rs
+++ b/cli/src/main.rs
@@ -1,16 +1,33 @@
-extern crate roc;
+extern crate roc_gen;
 
-use roc::eval::Evaluated::*;
-use roc::eval::{call, eval, Evaluated};
-use roc::expr::Expr;
-use roc::parse;
-use roc::region::{Located, Region};
+use crate::helpers::{infer_expr, uniq_expr_with};
+use bumpalo::Bump;
+use inkwell::context::Context;
+use inkwell::module::Linkage;
+use inkwell::passes::PassManager;
+use inkwell::types::BasicType;
+use inkwell::OptimizationLevel;
+use roc_collections::all::ImMap;
+use roc_gen::llvm::build::{build_proc, build_proc_header, get_call_conventions};
+use roc_gen::llvm::convert::basic_type_from_layout;
+use roc_mono::expr::{Expr, Procs};
+use roc_mono::layout::Layout;
+use std::time::SystemTime;
+
+use inkwell::targets::{
+    CodeModel, FileType, InitializationConfig, RelocMode, Target, TargetTriple,
+};
 use std::fs::File;
 use std::io;
 use std::io::prelude::*;
+use std::path::Path;
+use target_lexicon::{Architecture, OperatingSystem, Triple, Vendor};
 
-fn main() -> std::io::Result<()> {
-    let argv = std::env::args().into_iter().collect::<Vec<String>>();
+pub mod helpers;
+
+fn main() -> io::Result<()> {
+    let now = SystemTime::now();
+    let argv = std::env::args().collect::<Vec<String>>();
 
     match argv.get(1) {
         Some(filename) => {
@@ -19,9 +36,15 @@ fn main() -> std::io::Result<()> {
 
             file.read_to_string(&mut contents)?;
 
-            let expr = parse::parse_string(contents.as_str()).unwrap();
+            let dest_filename = Path::new(filename).with_extension("o");
 
-            process_task(eval(expr))
+            gen(contents.as_str(), Triple::host(), &dest_filename);
+
+            let end_time = now.elapsed().unwrap();
+
+            println!("Finished in {} ms\n", end_time.as_millis());
+
+            Ok(())
         }
         None => {
             println!("Usage: roc FILENAME.roc");
@@ -31,109 +54,213 @@ fn main() -> std::io::Result<()> {
     }
 }
 
-fn process_task(evaluated: Evaluated) -> std::io::Result<()> {
-    match evaluated {
-        EvalError(region, problem) => {
-            println!(
-                "\n\u{001B}[4mruntime error\u{001B}[24m\n\n{} at {}\n",
-                format!("{}", problem),
-                format!("line {}, column {}", region.start_line, region.start_col)
-            );
+fn gen(src: &str, target: Triple, dest_filename: &Path) {
+    // Build the expr
+    let arena = Bump::new();
 
-            Ok(())
-        }
-        ApplyVariant(name, Some(mut vals)) => {
-            match name.as_str() {
-                "Echo" => {
-                    // Extract the string from the Echo variant.
-                    let string_to_be_displayed = match vals.pop() {
-                        Some(Str(payload)) => payload,
-                        Some(EvalError(region, err)) => {
-                            panic!(
-                                "RUNTIME ERROR in Echo: {} at {}",
-                                format!("{}", err),
-                                format!("line {}, column {}", region.start_line, region.start_col)
-                            );
-                        }
-                        Some(val) => {
-                            panic!("TYPE MISMATCH in Echo: {}", format!("{}", val));
-                        }
-                        None => {
-                            panic!("TYPE MISMATCH in Echo: None");
-                        }
-                    };
+    let (loc_expr, _output, _problems, subs, var, constraint, home, interns) =
+        uniq_expr_with(&arena, src, &ImMap::default());
 
-                    // Print the string to the console, since that's what Echo does!
-                    println!("{}", string_to_be_displayed);
+    let mut unify_problems = Vec::new();
+    let (content, mut subs) = infer_expr(subs, &mut unify_problems, &constraint, var);
 
-                    // Continue with the callback.
-                    let callback = vals.pop().unwrap();
+    let context = Context::create();
+    let module = context.create_module("app");
+    let builder = context.create_builder();
+    let fpm = PassManager::create(&module);
 
-                    process_task(call(
-                        Region {
-                            start_line: 0,
-                            start_col: 0,
-                            end_line: 0,
-                            end_col: 0,
-                        },
-                        callback,
-                        vec![with_zero_loc(Expr::EmptyRecord)],
-                    ))
-                }
-                "Read" => {
-                    // Read a line from from stdin, since that's what Read does!
-                    let mut input = String::new();
+    roc_gen::llvm::build::add_passes(&fpm);
 
-                    io::stdin().read_line(&mut input)?;
+    fpm.initialize();
 
-                    // Continue with the callback.
-                    let callback = vals.pop().unwrap();
+    // Compute main_fn_type before moving subs to Env
+    let pointer_bytes = target.pointer_width().unwrap().bytes() as u32;
+    let layout = Layout::from_content(&arena, content, &subs, pointer_bytes)
+    .unwrap_or_else(|err| panic!("Code gen error in test: could not convert to layout. Err was {:?} and Subs were {:?}", err, subs));
 
-                    process_task(call(
-                        Region {
-                            start_line: 0,
-                            start_col: 0,
-                            end_line: 0,
-                            end_col: 0,
-                        },
-                        callback,
-                        vec![with_zero_loc(Expr::Str(input.trim().to_string()))],
-                    ))
-                }
-                "Success" => {
-                    // We finished all our tasks. Great! No need to print anything.
-                    Ok(())
-                }
-                _ => {
-                    // We don't recognize this variant, so display it and exit.
-                    display_val(ApplyVariant(name, Some(vals)));
+    let execution_engine = module
+        .create_jit_execution_engine(OptimizationLevel::None)
+        .expect("Error creating JIT execution engine for test");
 
-                    Ok(())
-                }
-            }
-        }
-        output => {
-            // We don't recognize this value, so display it and exit.
-            display_val(output);
+    let ptr_bytes = execution_engine
+        .get_target_data()
+        .get_pointer_byte_size(None);
+    let main_fn_type =
+        basic_type_from_layout(&arena, &context, &layout, ptr_bytes).fn_type(&[], false);
+    let main_fn_name = "$Test.main";
 
-            Ok(())
+    // Compile and add all the Procs before adding main
+    let mut env = roc_gen::llvm::build::Env {
+        arena: &arena,
+        builder: &builder,
+        context: &context,
+        interns,
+        module: arena.alloc(module),
+        ptr_bytes,
+    };
+    let mut procs = Procs::default();
+    let mut ident_ids = env.interns.all_ident_ids.remove(&home).unwrap();
+
+    // Populate Procs and get the low-level Expr from the canonical Expr
+    let main_body = Expr::new(
+        &arena,
+        &mut subs,
+        loc_expr.value,
+        &mut procs,
+        home,
+        &mut ident_ids,
+        pointer_bytes,
+    );
+
+    // Put this module's ident_ids back in the interns, so we can use them in env.
+    env.interns.all_ident_ids.insert(home, ident_ids);
+
+    let mut headers = Vec::with_capacity(procs.len());
+
+    // Add all the Proc headers to the module.
+    // We have to do this in a separate pass first,
+    // because their bodies may reference each other.
+    for (symbol, opt_proc) in procs.as_map().into_iter() {
+        if let Some(proc) = opt_proc {
+            let (fn_val, arg_basic_types) = build_proc_header(&env, symbol, &proc);
+
+            headers.push((proc, fn_val, arg_basic_types));
         }
     }
-}
 
-fn with_zero_loc<T>(val: T) -> Located<T> {
-    Located::new(
-        val,
-        Region {
-            start_line: 0,
-            start_col: 0,
+    // Build each proc using its header info.
+    for (proc, fn_val, arg_basic_types) in headers {
+        // NOTE: This is here to be uncommented in case verification fails.
+        // (This approach means we don't have to defensively clone name here.)
+        //
+        // println!("\n\nBuilding and then verifying function {}\n\n", name);
+        build_proc(&env, proc, &procs, fn_val, arg_basic_types);
 
-            end_line: 0,
-            end_col: 0,
-        },
-    )
-}
+        if fn_val.verify(true) {
+            fpm.run_on(&fn_val);
+        } else {
+            // NOTE: If this fails, uncomment the above println to debug.
+            panic!(
+                "Non-main function failed LLVM verification. Uncomment the above println to debug!"
+            );
+        }
+    }
 
-fn display_val(evaluated: Evaluated) {
-    println!("\n\u{001B}[4mroc out\u{001B}[24m\n\n{}\n", evaluated);
+    // Add main to the module.
+    let cc = get_call_conventions(target.default_calling_convention().unwrap());
+    let main_fn = env.module.add_function(main_fn_name, main_fn_type, None);
+
+    main_fn.set_call_conventions(cc);
+    main_fn.set_linkage(Linkage::External);
+
+    // Add main's body
+    let basic_block = context.append_basic_block(main_fn, "entry");
+
+    builder.position_at_end(basic_block);
+
+    let ret = roc_gen::llvm::build::build_expr(
+        &env,
+        &ImMap::default(),
+        main_fn,
+        &main_body,
+        &Procs::default(),
+    );
+
+    builder.build_return(Some(&ret));
+
+    // Uncomment this to see the module's un-optimized LLVM instruction output:
+    // env.module.print_to_stderr();
+
+    if main_fn.verify(true) {
+        fpm.run_on(&main_fn);
+    } else {
+        panic!("Function {} failed LLVM verification.", main_fn_name);
+    }
+
+    // Verify the module
+    if let Err(errors) = env.module.verify() {
+        panic!("Errors defining module: {:?}", errors);
+    }
+
+    // Uncomment this to see the module's optimized LLVM instruction output:
+    // env.module.print_to_stderr();
+
+    // Emit the .o file
+
+    // NOTE: arch_str is *not* the same as the beginning of the magic target triple
+    // string! For example, if it's "x86-64" here, the magic target triple string
+    // will begin with "x86_64" (with an underscore) instead.
+    let arch_str = match target.architecture {
+        Architecture::X86_64 => {
+            Target::initialize_x86(&InitializationConfig::default());
+
+            "x86-64"
+        }
+        Architecture::Arm(_) => {
+            Target::initialize_arm(&InitializationConfig::default());
+
+            "arm"
+        }
+        Architecture::Wasm32 => {
+            Target::initialize_webassembly(&InitializationConfig::default());
+
+            "wasm32"
+        }
+        _ => panic!(
+            "TODO gracefully handle unsupported target architecture: {:?}",
+            target.architecture
+        ),
+    };
+
+    let opt = OptimizationLevel::Default;
+    let reloc = RelocMode::Default;
+    let model = CodeModel::Default;
+
+    // Best guide I've found on how to determine these magic strings:
+    //
+    // https://stackoverflow.com/questions/15036909/clang-how-to-list-supported-target-architectures
+    let target_triple_str = match target {
+        Triple {
+            architecture: Architecture::X86_64,
+            vendor: Vendor::Unknown,
+            operating_system: OperatingSystem::Linux,
+            ..
+        } => "x86_64-unknown-linux-gnu",
+        Triple {
+            architecture: Architecture::X86_64,
+            vendor: Vendor::Pc,
+            operating_system: OperatingSystem::Linux,
+            ..
+        } => "x86_64-pc-linux-gnu",
+        Triple {
+            architecture: Architecture::X86_64,
+            vendor: Vendor::Unknown,
+            operating_system: OperatingSystem::Darwin,
+            ..
+        } => "x86_64-unknown-darwin10",
+        Triple {
+            architecture: Architecture::X86_64,
+            vendor: Vendor::Apple,
+            operating_system: OperatingSystem::Darwin,
+            ..
+        } => "x86_64-apple-darwin10",
+        _ => panic!("TODO gracefully handle unsupported target: {:?}", target),
+    };
+    let target_machine = Target::from_name(arch_str)
+        .unwrap()
+        .create_target_machine(
+            &TargetTriple::create(target_triple_str),
+            arch_str,
+            "+avx2", // TODO this string was used uncritically from an example, and should be reexamined
+            opt,
+            reloc,
+            model,
+        )
+        .unwrap();
+
+    target_machine
+        .write_to_file(&env.module, FileType::Object, &dest_filename)
+        .expect("Writing .o file failed");
+
+    println!("\nSuccess! 🎉\n\n\t➡ {}\n", dest_filename.display());
 }
diff --git a/compiler/gen/Cargo.toml b/compiler/gen/Cargo.toml
index 5284f77506..8d4f1ce41d 100644
--- a/compiler/gen/Cargo.toml
+++ b/compiler/gen/Cargo.toml
@@ -38,6 +38,7 @@ inlinable_string = "0.1.0"
 # change the tag value in this Cargo.toml to point to that tag, and `cargo update`.
 # This way, GitHub Actions works and nobody's builds get broken.
 inkwell = { git = "https://github.com/rtfeldman/inkwell", tag = "llvm8-0.release2" }
+target-lexicon = "0.10"
 
 [dev-dependencies]
 roc_can = { path = "../can" }
diff --git a/compiler/gen/src/llvm/build.rs b/compiler/gen/src/llvm/build.rs
index 5d0f3afb12..d9842790f6 100644
--- a/compiler/gen/src/llvm/build.rs
+++ b/compiler/gen/src/llvm/build.rs
@@ -3,6 +3,7 @@ use bumpalo::Bump;
 use inkwell::builder::Builder;
 use inkwell::context::Context;
 use inkwell::module::{Linkage, Module};
+use inkwell::passes::PassManager;
 use inkwell::types::{BasicTypeEnum, IntType, StructType};
 use inkwell::values::BasicValueEnum::{self, *};
 use inkwell::values::{FunctionValue, IntValue, PointerValue, StructValue};
@@ -15,6 +16,7 @@ use roc_collections::all::ImMap;
 use roc_module::symbol::{Interns, Symbol};
 use roc_mono::expr::{Expr, Proc, Procs};
 use roc_mono::layout::{Builtin, Layout};
+use target_lexicon::CallingConvention;
 
 /// This is for Inkwell's FunctionValue::verify - we want to know the verification
 /// output in debug builds, but we don't want it to print to stdout in release builds!
@@ -45,6 +47,25 @@ impl<'a, 'ctx, 'env> Env<'a, 'ctx, 'env> {
     }
 }
 
+pub fn add_passes(fpm: &PassManager<FunctionValue<'_>>) {
+    // tail-call elimination is always on
+    fpm.add_instruction_combining_pass();
+    fpm.add_tail_call_elimination_pass();
+
+    // Enable more optimizations when running cargo test --release
+    if !cfg!(debug_assertions) {
+        fpm.add_reassociate_pass();
+        fpm.add_basic_alias_analysis_pass();
+        fpm.add_promote_memory_to_register_pass();
+        fpm.add_cfg_simplification_pass();
+        fpm.add_gvn_pass();
+        // TODO figure out why enabling any of these (even alone) causes LLVM to segfault
+        // fpm.add_strip_dead_prototypes_pass();
+        // fpm.add_dead_arg_elimination_pass();
+        // fpm.add_function_inlining_pass();
+    }
+}
+
 #[allow(clippy::cognitive_complexity)]
 pub fn build_expr<'a, 'ctx, 'env>(
     env: &Env<'a, 'ctx, 'env>,
@@ -1277,3 +1298,17 @@ fn list_set<'a, 'ctx, 'env>(
         ret_type.into(),
     )
 }
+
+/// Translates a target_lexicon::Triple to a LLVM calling convention u32
+/// as described in https://llvm.org/doxygen/namespacellvm_1_1CallingConv.html
+pub fn get_call_conventions(cc: CallingConvention) -> u32 {
+    use CallingConvention::*;
+
+    // For now, we're returning 0 for the C calling convention on all of these.
+    // Not sure if we should be picking something more specific!
+    match cc {
+        SystemV => 0,
+        WasmBasicCAbi => 0,
+        WindowsFastcall => 0,
+    }
+}
diff --git a/compiler/gen/test.asm b/compiler/gen/test.asm
new file mode 100644
index 0000000000..7c703ef496
--- /dev/null
+++ b/compiler/gen/test.asm
@@ -0,0 +1,4 @@
+	.text
+	.file	"my_module"
+
+	.section	".note.GNU-stack","",@progbits
diff --git a/compiler/gen/tests/helpers/eval.rs b/compiler/gen/tests/helpers/eval.rs
index ef3562d769..eaa2dab95e 100644
--- a/compiler/gen/tests/helpers/eval.rs
+++ b/compiler/gen/tests/helpers/eval.rs
@@ -1,42 +1,8 @@
-// Pointer size on current system
-pub const POINTER_SIZE: u32 = std::mem::size_of::<usize>() as u32;
-
-// 0 is the C calling convention - see https://llvm.org/doxygen/namespacellvm_1_1CallingConv.html
-pub const MAIN_CALLING_CONVENTION: u32 = 0;
-
-#[macro_export]
-macro_rules! get_fpm {
-    ($module:expr) => {{
-        let fpm = PassManager::create(&$module);
-
-        // tail-call elimination is always on
-        fpm.add_instruction_combining_pass();
-        fpm.add_tail_call_elimination_pass();
-
-        // Enable more optimizations when running cargo test --release
-        if !cfg!(debug_assertions) {
-            fpm.add_reassociate_pass();
-            fpm.add_basic_alias_analysis_pass();
-            fpm.add_promote_memory_to_register_pass();
-            fpm.add_cfg_simplification_pass();
-            fpm.add_gvn_pass();
-            // TODO figure out why enabling any of these (even alone) causes LLVM to segfault
-            // fpm.add_strip_dead_prototypes_pass();
-            // fpm.add_dead_arg_elimination_pass();
-            // fpm.add_function_inlining_pass();
-        }
-
-        fpm.initialize();
-
-        // TODO when should we call initialize, and then finalize?
-
-        fpm
-    }};
-}
-
 #[macro_export]
 macro_rules! assert_llvm_evals_to {
     ($src:expr, $expected:expr, $ty:ty, $transform:expr) => {
+        let target = target_lexicon::Triple::host();
+        let ptr_bytes = target.pointer_width().unwrap().bytes() as u32;
         let arena = Bump::new();
         let CanExprOut { loc_expr, var_store, var, constraint, home, interns, .. } = can_expr($src);
         let subs = Subs::new(var_store.into());
@@ -46,18 +12,20 @@ macro_rules! assert_llvm_evals_to {
         let context = Context::create();
         let module = context.create_module("app");
         let builder = context.create_builder();
-        let fpm = { get_fpm!(module) };
+        let fpm = inkwell::passes::PassManager::create(&module);
+
+        roc_gen::llvm::build::add_passes(&fpm);
+
+        fpm.initialize();
 
         // Compute main_fn_type before moving subs to Env
-        let layout = Layout::from_content(&arena, content, &subs, $crate::helpers::eval::POINTER_SIZE)
+        let layout = Layout::from_content(&arena, content, &subs, ptr_bytes)
     .unwrap_or_else(|err| panic!("Code gen error in test: could not convert to layout. Err was {:?} and Subs were {:?}", err, subs));
         let execution_engine =
             module
             .create_jit_execution_engine(OptimizationLevel::None)
             .expect("Error creating JIT execution engine for test");
 
-        let ptr_bytes = execution_engine.get_target_data().get_pointer_byte_size(None);
-
         let main_fn_type = basic_type_from_layout(&arena, &context, &layout, ptr_bytes)
             .fn_type(&[], false);
         let main_fn_name = "$Test.main";
@@ -75,7 +43,7 @@ macro_rules! assert_llvm_evals_to {
         let mut ident_ids = env.interns.all_ident_ids.remove(&home).unwrap();
 
         // Populate Procs and get the low-level Expr from the canonical Expr
-        let main_body = Expr::new(&arena, &mut subs, loc_expr.value, &mut procs, home, &mut ident_ids, $crate::helpers::eval::POINTER_SIZE);
+        let main_body = Expr::new(&arena, &mut subs, loc_expr.value, &mut procs, home, &mut ident_ids, ptr_bytes);
 
         // Put this module's ident_ids back in the interns, so we can use them in Env.
         env.interns.all_ident_ids.insert(home, ident_ids);
@@ -111,8 +79,9 @@ macro_rules! assert_llvm_evals_to {
 
         // Add main to the module.
         let main_fn = env.module.add_function(main_fn_name, main_fn_type, None);
+        let cc = roc_gen::llvm::build::get_call_conventions(target.default_calling_convention().unwrap());
 
-        main_fn.set_call_conventions($crate::helpers::eval::MAIN_CALLING_CONVENTION);
+        main_fn.set_call_conventions(cc);
 
         // Add main's body
         let basic_block = context.append_basic_block(main_fn, "entry");
@@ -165,6 +134,8 @@ macro_rules! assert_llvm_evals_to {
 macro_rules! assert_opt_evals_to {
     ($src:expr, $expected:expr, $ty:ty, $transform:expr) => {
         let arena = Bump::new();
+        let target = target_lexicon::Triple::host();
+        let ptr_bytes = target.pointer_width().unwrap().bytes() as u32;
         let (loc_expr, _output, _problems, subs, var, constraint, home, interns) = uniq_expr($src);
 
         let mut unify_problems = Vec::new();
@@ -173,10 +144,142 @@ macro_rules! assert_opt_evals_to {
         let context = Context::create();
         let module = context.create_module("app");
         let builder = context.create_builder();
-        let fpm = { get_fpm!(module) };
+        let fpm = PassManager::create(&module);
+
+        roc_gen::llvm::build::add_passes(&fpm);
+
+        fpm.initialize();
 
         // Compute main_fn_type before moving subs to Env
-        let layout = Layout::from_content(&arena, content, &subs, $crate::helpers::eval::POINTER_SIZE)
+        let layout = Layout::from_content(&arena, content, &subs, ptr_bytes)
+    .unwrap_or_else(|err| panic!("Code gen error in test: could not convert to layout. Err was {:?} and Subs were {:?}", err, subs));
+
+        let execution_engine =
+            module
+            .create_jit_execution_engine(OptimizationLevel::None)
+            .expect("Error creating JIT execution engine for test");
+
+        let main_fn_type = basic_type_from_layout(&arena, &context, &layout, ptr_bytes)
+            .fn_type(&[], false);
+        let main_fn_name = "$Test.main";
+
+        // Compile and add all the Procs before adding main
+        let mut env = roc_gen::llvm::build::Env {
+            arena: &arena,
+            builder: &builder,
+            context: &context,
+            interns,
+            module: arena.alloc(module),
+            ptr_bytes
+        };
+        let mut procs = Procs::default();
+        let mut ident_ids = env.interns.all_ident_ids.remove(&home).unwrap();
+
+        // Populate Procs and get the low-level Expr from the canonical Expr
+        let main_body = Expr::new(&arena, &mut subs, loc_expr.value, &mut procs, home, &mut ident_ids, ptr_bytes);
+
+        // Put this module's ident_ids back in the interns, so we can use them in Env.
+        env.interns.all_ident_ids.insert(home, ident_ids);
+
+        let mut headers = Vec::with_capacity(procs.len());
+
+        // Add all the Proc headers to the module.
+        // We have to do this in a separate pass first,
+        // because their bodies may reference each other.
+        for (symbol, opt_proc) in procs.as_map().into_iter() {
+            if let Some(proc) = opt_proc {
+                let (fn_val, arg_basic_types) = build_proc_header(&env, symbol, &proc);
+
+                headers.push((proc, fn_val, arg_basic_types));
+            }
+        }
+
+        // Build each proc using its header info.
+        for (proc, fn_val, arg_basic_types) in headers {
+            // NOTE: This is here to be uncommented in case verification fails.
+            // (This approach means we don't have to defensively clone name here.)
+            //
+            // println!("\n\nBuilding and then verifying function {}\n\n", name);
+            build_proc(&env, proc, &procs, fn_val, arg_basic_types);
+
+            if fn_val.verify(true) {
+                fpm.run_on(&fn_val);
+            } else {
+                // NOTE: If this fails, uncomment the above println to debug.
+                panic!("Non-main function failed LLVM verification. Uncomment the above println to debug!");
+            }
+        }
+
+        // Add main to the module.
+        let main_fn = env.module.add_function(main_fn_name, main_fn_type, None);
+        let cc = roc_gen::llvm::build::get_call_conventions(target.default_calling_convention().unwrap());
+
+        main_fn.set_call_conventions(cc);
+
+        // Add main's body
+        let basic_block = context.append_basic_block(main_fn, "entry");
+
+        builder.position_at_end(basic_block);
+
+        let ret = roc_gen::llvm::build::build_expr(
+            &env,
+            &ImMap::default(),
+            main_fn,
+            &main_body,
+            &mut Procs::default(),
+        );
+
+        builder.build_return(Some(&ret));
+
+        // Uncomment this to see the module's un-optimized LLVM instruction output:
+        // env.module.print_to_stderr();
+
+        if main_fn.verify(true) {
+            fpm.run_on(&main_fn);
+        } else {
+            panic!("Function {} failed LLVM verification.", main_fn_name);
+        }
+
+        // Verify the module
+        if let Err(errors) = env.module.verify() {
+            panic!("Errors defining module: {:?}", errors);
+        }
+
+        // Uncomment this to see the module's optimized LLVM instruction output:
+        // env.module.print_to_stderr();
+
+        unsafe {
+            let main: JitFunction<unsafe extern "C" fn() -> $ty> = execution_engine
+                .get_function(main_fn_name)
+                .ok()
+                .ok_or(format!("Unable to JIT compile `{}`", main_fn_name))
+                .expect("errored");
+
+            assert_eq!($transform(main.call()), $expected);
+        }
+    };
+}
+
+#[macro_export]
+macro_rules! emit_expr {
+    ($src:expr, $expected:expr, $ty:ty, $transform:expr) => {
+        let arena = Bump::new();
+        let (loc_expr, _output, _problems, subs, var, constraint, home, interns) = uniq_expr($src);
+
+        let mut unify_problems = Vec::new();
+        let (content, mut subs) = infer_expr(subs, &mut unify_problems, &constraint, var);
+
+        let context = Context::create();
+        let module = context.create_module("app");
+        let builder = context.create_builder();
+        let fpm = PassManager::create(&module);
+
+        roc_gen::llvm::build::add_passes(&fpm);
+
+        fpm.initialize();
+
+        // Compute main_fn_type before moving subs to Env
+        let layout = Layout::from_content(&arena, content, &subs, ptr_bytes)
     .unwrap_or_else(|err| panic!("Code gen error in test: could not convert to layout. Err was {:?} and Subs were {:?}", err, subs));
 
         let execution_engine =
@@ -184,7 +287,6 @@ macro_rules! assert_opt_evals_to {
             .create_jit_execution_engine(OptimizationLevel::None)
             .expect("Error creating JIT execution engine for test");
 
-        let ptr_bytes = execution_engine.get_target_data().get_pointer_byte_size(None);
         let main_fn_type = basic_type_from_layout(&arena, &context, &layout, ptr_bytes)
             .fn_type(&[], false);
         let main_fn_name = "$Test.main";
@@ -218,7 +320,6 @@ macro_rules! assert_opt_evals_to {
 
                 headers.push((proc, fn_val, arg_basic_types));
             }
-
         }
 
         // Build each proc using its header info.
diff --git a/compiler/mono/Cargo.toml b/compiler/mono/Cargo.toml
index 67eae0c3aa..f2e3bb270b 100644
--- a/compiler/mono/Cargo.toml
+++ b/compiler/mono/Cargo.toml
@@ -11,12 +11,12 @@ roc_module = { path = "../module" }
 roc_types = { path = "../types" }
 roc_can = { path = "../can" }
 roc_unify = { path = "../unify" }
+roc_problem = { path = "../problem" }
 bumpalo = { version = "3.2", features = ["collections"] }
 
 [dev-dependencies]
 roc_constrain = { path = "../constrain" }
 roc_builtins = { path = "../builtins" }
-roc_problem = { path = "../problem" }
 roc_parse = { path = "../parse" }
 roc_solve = { path = "../solve" }
 pretty_assertions = "0.5.1 "
diff --git a/compiler/mono/src/expr.rs b/compiler/mono/src/expr.rs
index f3846d224b..a79bb8609f 100644
--- a/compiler/mono/src/expr.rs
+++ b/compiler/mono/src/expr.rs
@@ -340,31 +340,43 @@ fn pattern_to_when<'a>(
             // for underscore we generate a dummy Symbol
             (env.fresh_symbol(), body)
         }
-
-        Shadowed(_, _) | UnsupportedPattern(_) => {
-            // create the runtime error here, instead of delegating to When.
-            // UnsupportedPattern should then never occcur in When
-            panic!("TODO generate runtime error here");
+        Shadowed(region, loc_ident) => {
+            let error = roc_problem::can::RuntimeError::Shadowing {
+                original_region: *region,
+                shadow: loc_ident.clone(),
+            };
+            (env.fresh_symbol(), Located::at_zero(RuntimeError(error)))
         }
 
-        AppliedTag {..} | RecordDestructure {..} => {
+        UnsupportedPattern(region) => {
+            // create the runtime error here, instead of delegating to When.
+            // UnsupportedPattern should then never occcur in When
+            let error = roc_problem::can::RuntimeError::UnsupportedPattern(*region);
+            (env.fresh_symbol(), Located::at_zero(RuntimeError(error)))
+        }
+
+        AppliedTag { .. } | RecordDestructure { .. } => {
             let symbol = env.fresh_symbol();
 
             let wrapped_body = When {
                 cond_var: pattern_var,
                 expr_var: body_var,
                 loc_cond: Box::new(Located::at_zero(Var(symbol))),
-                branches: vec![WhenBranch{ patterns: vec![pattern], value: body, guard: None }],
+                branches: vec![WhenBranch {
+                    patterns: vec![pattern],
+                    value: body,
+                    guard: None,
+                }],
             };
 
             (symbol, Located::at_zero(wrapped_body))
         }
 
-        // These patters are refutable, and thus should never occur outside a `when` expression
-        IntLiteral(_) | NumLiteral(_,_) | FloatLiteral(_) | StrLiteral(_) => {
+        IntLiteral(_) | NumLiteral(_, _) | FloatLiteral(_) | StrLiteral(_) => {
+            // These patters are refutable, and thus should never occur outside a `when` expression
+            // They should have been replaced with `UnsupportedPattern` during canonicalization
             unreachable!("refutable pattern {:?} where irrefutable pattern is expected. This should never happen!", pattern.value)
         }
-
     }
 }
 
@@ -1019,7 +1031,7 @@ fn from_can_when<'a>(
     if branches.is_empty() {
         // A when-expression with no branches is a runtime error.
         // We can't know what to return!
-        panic!("TODO compile a 0-branch when-expression to a RuntimeError");
+        Expr::RuntimeError("Hit a 0-branch when expression")
     } else if branches.len() == 1 && branches[0].patterns.len() == 1 && branches[0].guard.is_none()
     {
         let first = branches.remove(0);
diff --git a/compiler/problem/src/can.rs b/compiler/problem/src/can.rs
index 892b628f34..4ecb4aa0ce 100644
--- a/compiler/problem/src/can.rs
+++ b/compiler/problem/src/can.rs
@@ -34,6 +34,8 @@ pub enum RuntimeError {
         original_region: Region,
         shadow: Located<Ident>,
     },
+    // Example: (5 = 1 + 2) is an unsupported pattern in an assignment; Int patterns aren't allowed in assignments!
+    UnsupportedPattern(Region),
     UnrecognizedFunctionName(Located<InlinableString>),
     LookupNotInScope(Located<InlinableString>),
     ValueNotExposed {
diff --git a/compiler/solve/tests/test_solve.rs b/compiler/solve/tests/test_solve.rs
index 1adbff44a2..74737921c9 100644
--- a/compiler/solve/tests/test_solve.rs
+++ b/compiler/solve/tests/test_solve.rs
@@ -2526,4 +2526,27 @@ mod test_solve {
             "List a -> List a",
         );
     }
+
+    #[cfg(debug_assertions)]
+    #[test]
+    #[should_panic]
+    fn rigid_record_quantification() {
+        // the ext here is qualified on the outside (because we have rank 1 types, not rank 2).
+        // That means e.g. `f : { bar : String, foo : Int } -> Bool }` is a valid argument. but
+        // that function could not be applied to the `{ foo : Int }` list. Therefore, this function
+        // is not allowed.
+        //
+        // should hit a debug_assert! in debug mode, and produce a type error in release mode
+        infer_eq_without_problem(
+            indoc!(
+                r#"
+                test : ({ foo : Int }ext -> Bool), { foo : Int } -> Bool
+                test = \fn, a -> fn a
+
+                test
+                "#
+            ),
+            "should fail",
+        );
+    }
 }
diff --git a/examples/hello-world/.gitignore b/examples/hello-world/.gitignore
new file mode 100644
index 0000000000..b9780edc19
--- /dev/null
+++ b/examples/hello-world/.gitignore
@@ -0,0 +1,3 @@
+hello
+*.o
+*.so
diff --git a/examples/hello-world/README.md b/examples/hello-world/README.md
new file mode 100644
index 0000000000..4add6731ed
--- /dev/null
+++ b/examples/hello-world/README.md
@@ -0,0 +1,232 @@
+# Hello, World!
+
+Right now, there is only one way to build Roc programs: the Rube Goldberg Build Process.
+(In the future, it will be nicer. At the moment, the nicer build system exists only 
+in our imaginations...so Rube Goldberg it is!)
+
+## Ingredients
+
+1. A host. For this example, our host is implemented in the file `host.rs`.
+2. A Roc function. For this example, we'll use a function which returns the Roc string `"Hello, World!"`
+3. Having `gcc` installed. This will not be necessary in the future, but the Rube Goldberg build process needs it.
+
+## Steps
+
+1. `cd` into `examples/hello-world/`
+2. Run `cargo run hello.roc` to compile the Roc source code into a `hello.o` file.
+3. Run `gcc -shared hello.o -o libhello_from_roc.so` to generate `libhello_from_roc.so`. (This filename must begin with `lib` and end in `.so` or else `host.rs` won't be able to find it!)
+4. Move `libhello_from_roc.so` onto the system library path, e.g. with `sudo mv libhello_from_roc.so /usr/local/lib/`
+5. Run `rustc host.rs -o hello` to generate the `hello` executable.
+6. Run `./hello` to see the greeting!
+
+To run in release mode instead, do:
+
+```bash
+cargo run --release hello.roc
+```
+
+## Design Notes
+
+This demonstrates the basic design of hosts: Roc code gets compiled into a pure 
+function (in this case, a thunk that always returns `"Hello, World!"`) and
+then the host calls that function. Fundamentally, that's the whole idea! The host
+might not even have a `main` - it could be a library, a plugin, anything.
+Everything else is built on this basic "hosts calling linked pure functions" design.
+
+For example, things get more interesting when the compiled Roc function returns
+a `Task` - that is, a tagged union data structure containing function pointers 
+to callback closures. This lets the Roc pure function describe arbitrary 
+chainable effects, which the host can interpret to perform I/O as requested by 
+the Roc program.  (The tagged union `Task` would have a variant for each supported 
+I/O operation.)
+
+In this trivial example, it's very easy to line up the API between the host and
+the Roc program. In a more involved host, this would be much trickier - especially
+if the API were changing frequently during development.
+
+The idea there is to have a first-class concept of "glue code" which host authors
+can write (it would be plain Roc code, but with some extra keywords that aren't
+available in normal modules - kinda like `port module` in Elm), and which
+describe both the Roc-host/C boundary as well as the Roc-host/Roc-app boundary.
+Roc application authors only care about the Roc-host/Roc-app portion, and the
+host author only cares about the Roc-host/C bounary when implementing the host.
+
+Using this glue code, the Roc compiler can generate C header files describing the
+boundary. This not only gets us host compatibility with C compilers, but also 
+Rust FFI for free, because [`rust-bindgen`](https://github.com/rust-lang/rust-bindgen) 
+generates correct Rust FFI bindings from C headers.
+
+The whole "calling gcc and rustc" part of the current build process is obviously
+not something Roc application authors should ever need to do. Rather, the idea
+would be to have the host precompiled into an object file (eliminating the
+need for Roc authors to run `rustc` in this example) and for the Roc compiler
+to not only generate the object file for the Roc file, but also to link it with
+the host object file to produce an executable (eliminating the need for `gcc`)
+such that Roc application authors can concern themselves exclusively with Roc code
+and need only the Roc compiler to build and to execute it.
+
+Of course, none of those niceties exist yet. But we'll get there!
+
+## The test that builds things
+
+```rust
+let src = indoc!(
+    r#"
+    "Hello, World!"
+    "#
+);
+
+// Build the expr
+let arena = Bump::new();
+let (loc_expr, _output, _problems, subs, var, constraint, home, interns) = uniq_expr(src);
+
+let mut unify_problems = Vec::new();
+let (content, mut subs) = infer_expr(subs, &mut unify_problems, &constraint, var);
+
+let context = Context::create();
+let module = context.create_module("app");
+let builder = context.create_builder();
+let fpm = PassManager::create(&module);
+
+roc_gen::llvm::build::add_passes(&fpm);
+
+fpm.initialize();
+
+// Compute main_fn_type before moving subs to Env
+let layout = Layout::from_content(&arena, content, &subs, crate::helpers::eval::POINTER_SIZE)
+.unwrap_or_else(|err| panic!("Code gen error in test: could not convert to layout. Err was {:?} and Subs were {:?}", err, subs));
+
+let execution_engine = module
+    .create_jit_execution_engine(OptimizationLevel::None)
+    .expect("Error creating JIT execution engine for test");
+
+let ptr_bytes = execution_engine
+    .get_target_data()
+    .get_pointer_byte_size(None);
+let main_fn_type =
+    basic_type_from_layout(&arena, &context, &layout, ptr_bytes).fn_type(&[], false);
+let main_fn_name = "$Test.main";
+
+// Compile and add all the Procs before adding main
+let mut env = roc_gen::llvm::build::Env {
+    arena: &arena,
+    builder: &builder,
+    context: &context,
+    interns,
+    module: arena.alloc(module),
+    ptr_bytes,
+};
+let mut procs = Procs::default();
+let mut ident_ids = env.interns.all_ident_ids.remove(&home).unwrap();
+
+// Populate Procs and get the low-level Expr from the canonical Expr
+let main_body = Expr::new(
+    &arena,
+    &mut subs,
+    loc_expr.value,
+    &mut procs,
+    home,
+    &mut ident_ids,
+    crate::helpers::eval::POINTER_SIZE,
+);
+
+// Put this module's ident_ids back in the interns, so we can use them in env.
+env.interns.all_ident_ids.insert(home, ident_ids);
+
+let mut headers = Vec::with_capacity(procs.len());
+
+// Add all the Proc headers to the module.
+// We have to do this in a separate pass first,
+// because their bodies may reference each other.
+for (symbol, opt_proc) in procs.as_map().into_iter() {
+    if let Some(proc) = opt_proc {
+        let (fn_val, arg_basic_types) = build_proc_header(&env, symbol, &proc);
+
+        headers.push((proc, fn_val, arg_basic_types));
+    }
+}
+
+// Build each proc using its header info.
+for (proc, fn_val, arg_basic_types) in headers {
+    // NOTE: This is here to be uncommented in case verification fails.
+    // (This approach means we don't have to defensively clone name here.)
+    //
+    // println!("\n\nBuilding and then verifying function {}\n\n", name);
+    build_proc(&env, proc, &procs, fn_val, arg_basic_types);
+
+    if fn_val.verify(true) {
+        fpm.run_on(&fn_val);
+    } else {
+        // NOTE: If this fails, uncomment the above println to debug.
+        panic!("Non-main function failed LLVM verification. Uncomment the above println to debug!");
+    }
+}
+
+// Add main to the module.
+let main_fn = env.module.add_function(main_fn_name, main_fn_type, None);
+
+main_fn.set_call_conventions(crate::helpers::eval::MAIN_CALLING_CONVENTION);
+main_fn.set_linkage(Linkage::External);
+
+// Add main's body
+let basic_block = context.append_basic_block(main_fn, "entry");
+
+builder.position_at_end(basic_block);
+
+let ret = roc_gen::llvm::build::build_expr(
+    &env,
+    &ImMap::default(),
+    main_fn,
+    &main_body,
+    &mut Procs::default(),
+);
+
+builder.build_return(Some(&ret));
+
+// Uncomment this to see the module's un-optimized LLVM instruction output:
+// env.module.print_to_stderr();
+
+if main_fn.verify(true) {
+    fpm.run_on(&main_fn);
+} else {
+    panic!("Function {} failed LLVM verification.", main_fn_name);
+}
+
+// Verify the module
+if let Err(errors) = env.module.verify() {
+    panic!("Errors defining module: {:?}", errors);
+}
+
+// Uncomment this to see the module's optimized LLVM instruction output:
+// env.module.print_to_stderr();
+
+// Emit
+Target::initialize_x86(&InitializationConfig::default());
+
+let opt = OptimizationLevel::Default;
+let reloc = RelocMode::Default;
+let model = CodeModel::Default;
+let target = Target::from_name("x86-64").unwrap();
+let target_machine = target
+    .create_target_machine(
+        &TargetTriple::create("x86_64-pc-linux-gnu"),
+        "x86-64",
+        "+avx2",
+        opt,
+        reloc,
+        model,
+    )
+    .unwrap();
+
+let path = Path::new("../../hello.o");
+
+assert!(target_machine
+    .write_to_file(&env.module, FileType::Object, &path)
+    .is_ok());
+
+let path = Path::new("../../hello.asm");
+
+assert!(target_machine
+    .write_to_file(&env.module, FileType::Assembly, &path)
+    .is_ok());
+```
diff --git a/examples/hello-world/hello.roc b/examples/hello-world/hello.roc
new file mode 100644
index 0000000000..b0d555865b
--- /dev/null
+++ b/examples/hello-world/hello.roc
@@ -0,0 +1 @@
+"Hello, World!"
diff --git a/examples/hello-world/host b/examples/hello-world/host
new file mode 100755
index 0000000000..16cb34082a
Binary files /dev/null and b/examples/hello-world/host differ
diff --git a/examples/hello-world/host.rs b/examples/hello-world/host.rs
new file mode 100644
index 0000000000..ce620637d0
--- /dev/null
+++ b/examples/hello-world/host.rs
@@ -0,0 +1,14 @@
+use std::ffi::CStr;
+use std::os::raw::c_char;
+
+#[link(name = "hello_from_roc")]
+extern "C" {
+    #[link_name = "$Test.main"]
+    fn str_from_roc() -> *const c_char;
+}
+
+pub fn main() {
+    let c_str = unsafe { CStr::from_ptr(str_from_roc()) };
+
+    println!("Roc says: {}", c_str.to_str().unwrap());
+}
diff --git a/hello b/hello
new file mode 100755
index 0000000000..d1cec61d54
Binary files /dev/null and b/hello differ
diff --git a/hello.asm b/hello.asm
new file mode 100644
index 0000000000..c608634521
--- /dev/null
+++ b/hello.asm
@@ -0,0 +1,24 @@
+	.text
+	.file	"app"
+	.globl	$Test.main
+	.p2align	4, 0x90
+	.type	$Test.main,@function
+$Test.main:
+	.cfi_startproc
+	pushq	%rax
+	.cfi_def_cfa_offset 16
+	movl	$14, %edi
+	callq	malloc
+	movabsq	$6278066737626506568, %rcx
+	movq	%rcx, (%rax)
+	movl	$1684828783, 8(%rax)
+	movw	$33, 12(%rax)
+	popq	%rcx
+	.cfi_def_cfa_offset 8
+	retq
+.Lfunc_end0:
+	.size	$Test.main, .Lfunc_end0-($Test.main)
+	.cfi_endproc
+
+
+	.section	".note.GNU-stack","",@progbits
diff --git a/hello.o b/hello.o
new file mode 100644
index 0000000000..de6b3788b2
Binary files /dev/null and b/hello.o differ
diff --git a/hello.so b/hello.so
new file mode 100755
index 0000000000..42cca021e2
Binary files /dev/null and b/hello.so differ
diff --git a/lib b/lib
new file mode 100755
index 0000000000..53971be50e
Binary files /dev/null and b/lib differ
diff --git a/out.asm b/out.asm
new file mode 100644
index 0000000000..6d2c4a86f1
--- /dev/null
+++ b/out.asm
@@ -0,0 +1,32 @@
+	.text
+	.file	"app"
+	.p2align	4, 0x90
+	.type	.L_0,@function
+.L_0:
+	.cfi_startproc
+	movq	%rdi, %rax
+	movq	%rdi, %rdx
+	retq
+.Lfunc_end0:
+	.size	.L_0, .Lfunc_end0-.L_0
+	.cfi_endproc
+
+	.globl	$Test.main
+	.p2align	4, 0x90
+	.type	$Test.main,@function
+$Test.main:
+	.cfi_startproc
+	pushq	%rax
+	.cfi_def_cfa_offset 16
+	movl	$9, %edi
+	callq	.L_0
+	imulq	%rdx, %rax
+	popq	%rcx
+	.cfi_def_cfa_offset 8
+	retq
+.Lfunc_end1:
+	.size	$Test.main, .Lfunc_end1-($Test.main)
+	.cfi_endproc
+
+
+	.section	".note.GNU-stack","",@progbits
diff --git a/out2.asm b/out2.asm
new file mode 100644
index 0000000000..23fdd0bcff
--- /dev/null
+++ b/out2.asm
@@ -0,0 +1,395 @@
+00000000  7F45              jg 0x47
+00000002  4C                rex.wr
+00000003  460201            add r8b,[rcx]
+00000006  0100              add [rax],eax
+00000008  0000              add [rax],al
+0000000A  0000              add [rax],al
+0000000C  0000              add [rax],al
+0000000E  0000              add [rax],al
+00000010  0100              add [rax],eax
+00000012  3E0001            add [ds:rcx],al
+00000015  0000              add [rax],al
+00000017  0000              add [rax],al
+00000019  0000              add [rax],al
+0000001B  0000              add [rax],al
+0000001D  0000              add [rax],al
+0000001F  0000              add [rax],al
+00000021  0000              add [rax],al
+00000023  0000              add [rax],al
+00000025  0000              add [rax],al
+00000027  008001000000      add [rax+0x1],al
+0000002D  0000              add [rax],al
+0000002F  0000              add [rax],al
+00000031  0000              add [rax],al
+00000033  004000            add [rax+0x0],al
+00000036  0000              add [rax],al
+00000038  0000              add [rax],al
+0000003A  400007            add [rdi],al
+0000003D  0001              add [rcx],al
+0000003F  004889            add [rax-0x77],cl
+00000042  F8                clc
+00000043  4889FA            mov rdx,rdi
+00000046  C3                ret
+00000047  660F1F8400000000  nop word [rax+rax+0x0]
+         -00
+00000050  50                push rax
+00000051  BF09000000        mov edi,0x9
+00000056  E8E5FFFFFF        call 0x40
+0000005B  4801D0            add rax,rdx
+0000005E  59                pop rcx
+0000005F  C3                ret
+00000060  1400              adc al,0x0
+00000062  0000              add [rax],al
+00000064  0000              add [rax],al
+00000066  0000              add [rax],al
+00000068  017A52            add [rdx+0x52],edi
+0000006B  0001              add [rcx],al
+0000006D  7810              js 0x7f
+0000006F  011B              add [rbx],ebx
+00000071  0C07              or al,0x7
+00000073  089001000010      or [rax+0x10000001],dl
+00000079  0000              add [rax],al
+0000007B  001C00            add [rax+rax],bl
+0000007E  0000              add [rax],al
+00000080  0000              add [rax],al
+00000082  0000              add [rax],al
+00000084  07                db 0x07
+00000085  0000              add [rax],al
+00000087  0000              add [rax],al
+00000089  0000              add [rax],al
+0000008B  0018              add [rax],bl
+0000008D  0000              add [rax],al
+0000008F  0030              add [rax],dh
+00000091  0000              add [rax],al
+00000093  0000              add [rax],al
+00000095  0000              add [rax],al
+00000097  0010              add [rax],dl
+00000099  0000              add [rax],al
+0000009B  0000              add [rax],al
+0000009D  41                rex.b
+0000009E  0E                db 0x0e
+0000009F  104E0E            adc [rsi+0xe],cl
+000000A2  0800              or [rax],al
+000000A4  0000              add [rax],al
+000000A6  0000              add [rax],al
+000000A8  0000              add [rax],al
+000000AA  0000              add [rax],al
+000000AC  0000              add [rax],al
+000000AE  0000              add [rax],al
+000000B0  0000              add [rax],al
+000000B2  0000              add [rax],al
+000000B4  0000              add [rax],al
+000000B6  0000              add [rax],al
+000000B8  0000              add [rax],al
+000000BA  0000              add [rax],al
+000000BC  0000              add [rax],al
+000000BE  0000              add [rax],al
+000000C0  07                db 0x07
+000000C1  0000              add [rax],al
+000000C3  000400            add [rax+rax],al
+000000C6  F1                int1
+000000C7  FF00              inc dword [rax]
+000000C9  0000              add [rax],al
+000000CB  0000              add [rax],al
+000000CD  0000              add [rax],al
+000000CF  0000              add [rax],al
+000000D1  0000              add [rax],al
+000000D3  0000              add [rax],al
+000000D5  0000              add [rax],al
+000000D7  0000              add [rax],al
+000000D9  0000              add [rax],al
+000000DB  0003              add [rbx],al
+000000DD  0002              add [rdx],al
+000000DF  0000              add [rax],al
+000000E1  0000              add [rax],al
+000000E3  0000              add [rax],al
+000000E5  0000              add [rax],al
+000000E7  0000              add [rax],al
+000000E9  0000              add [rax],al
+000000EB  0000              add [rax],al
+000000ED  0000              add [rax],al
+000000EF  000B              add [rbx],cl
+000000F1  0000              add [rax],al
+000000F3  0012              add [rdx],dl
+000000F5  0002              add [rdx],al
+000000F7  0010              add [rax],dl
+000000F9  0000              add [rax],al
+000000FB  0000              add [rax],al
+000000FD  0000              add [rax],al
+000000FF  0010              add [rax],dl
+00000101  0000              add [rax],al
+00000103  0000              add [rax],al
+00000105  0000              add [rax],al
+00000107  0020              add [rax],ah
+00000109  0000              add [rax],al
+0000010B  0000              add [rax],al
+0000010D  0000              add [rax],al
+0000010F  0002              add [rdx],al
+00000111  0000              add [rax],al
+00000113  0002              add [rdx],al
+00000115  0000              add [rax],al
+00000117  0000              add [rax],al
+00000119  0000              add [rax],al
+0000011B  0000              add [rax],al
+0000011D  0000              add [rax],al
+0000011F  003400            add [rax+rax],dh
+00000122  0000              add [rax],al
+00000124  0000              add [rax],al
+00000126  0000              add [rax],al
+00000128  0200              add al,[rax]
+0000012A  0000              add [rax],al
+0000012C  0200              add al,[rax]
+0000012E  0000              add [rax],al
+00000130  1000              adc [rax],al
+00000132  0000              add [rax],al
+00000134  0000              add [rax],al
+00000136  0000              add [rax],al
+00000138  002E              add [rsi],ch
+0000013A  7465              jz 0x1a1
+0000013C  7874              js 0x1b2
+0000013E  006170            add [rcx+0x70],ah
+00000141  7000              jo 0x143
+00000143  2454              and al,0x54
+00000145  657374            gs jnc 0x1bc
+00000148  2E6D              cs insd
+0000014A  61                db 0x61
+0000014B  696E002E6E6F74    imul ebp,[rsi+0x0],dword 0x746f6e2e
+00000152  65                gs
+00000153  2E                cs
+00000154  47                rex.rxb
+00000155  4E55              push rbp
+00000157  2D73746163        sub eax,0x63617473
+0000015C  6B002E            imul eax,[rax],byte +0x2e
+0000015F  7265              jc 0x1c6
+00000161  6C                insb
+00000162  61                db 0x61
+00000163  2E65685F667261    gs push qword 0x6172665f
+0000016A  6D                insd
+0000016B  65002E            add [gs:rsi],ch
+0000016E  7374              jnc 0x1e4
+00000170  7274              jc 0x1e6
+00000172  61                db 0x61
+00000173  62                db 0x62
+00000174  002E              add [rsi],ch
+00000176  7379              jnc 0x1f1
+00000178  6D                insd
+00000179  7461              jz 0x1dc
+0000017B  62                db 0x62
+0000017C  0000              add [rax],al
+0000017E  0000              add [rax],al
+00000180  0000              add [rax],al
+00000182  0000              add [rax],al
+00000184  0000              add [rax],al
+00000186  0000              add [rax],al
+00000188  0000              add [rax],al
+0000018A  0000              add [rax],al
+0000018C  0000              add [rax],al
+0000018E  0000              add [rax],al
+00000190  0000              add [rax],al
+00000192  0000              add [rax],al
+00000194  0000              add [rax],al
+00000196  0000              add [rax],al
+00000198  0000              add [rax],al
+0000019A  0000              add [rax],al
+0000019C  0000              add [rax],al
+0000019E  0000              add [rax],al
+000001A0  0000              add [rax],al
+000001A2  0000              add [rax],al
+000001A4  0000              add [rax],al
+000001A6  0000              add [rax],al
+000001A8  0000              add [rax],al
+000001AA  0000              add [rax],al
+000001AC  0000              add [rax],al
+000001AE  0000              add [rax],al
+000001B0  0000              add [rax],al
+000001B2  0000              add [rax],al
+000001B4  0000              add [rax],al
+000001B6  0000              add [rax],al
+000001B8  0000              add [rax],al
+000001BA  0000              add [rax],al
+000001BC  0000              add [rax],al
+000001BE  0000              add [rax],al
+000001C0  3500000003        xor eax,0x3000000
+000001C5  0000              add [rax],al
+000001C7  0000              add [rax],al
+000001C9  0000              add [rax],al
+000001CB  0000              add [rax],al
+000001CD  0000              add [rax],al
+000001CF  0000              add [rax],al
+000001D1  0000              add [rax],al
+000001D3  0000              add [rax],al
+000001D5  0000              add [rax],al
+000001D7  0038              add [rax],bh
+000001D9  0100              add [rax],eax
+000001DB  0000              add [rax],al
+000001DD  0000              add [rax],al
+000001DF  004500            add [rbp+0x0],al
+000001E2  0000              add [rax],al
+000001E4  0000              add [rax],al
+000001E6  0000              add [rax],al
+000001E8  0000              add [rax],al
+000001EA  0000              add [rax],al
+000001EC  0000              add [rax],al
+000001EE  0000              add [rax],al
+000001F0  0100              add [rax],eax
+000001F2  0000              add [rax],al
+000001F4  0000              add [rax],al
+000001F6  0000              add [rax],al
+000001F8  0000              add [rax],al
+000001FA  0000              add [rax],al
+000001FC  0000              add [rax],al
+000001FE  0000              add [rax],al
+00000200  0100              add [rax],eax
+00000202  0000              add [rax],al
+00000204  0100              add [rax],eax
+00000206  0000              add [rax],al
+00000208  06                db 0x06
+00000209  0000              add [rax],al
+0000020B  0000              add [rax],al
+0000020D  0000              add [rax],al
+0000020F  0000              add [rax],al
+00000211  0000              add [rax],al
+00000213  0000              add [rax],al
+00000215  0000              add [rax],al
+00000217  004000            add [rax+0x0],al
+0000021A  0000              add [rax],al
+0000021C  0000              add [rax],al
+0000021E  0000              add [rax],al
+00000220  2000              and [rax],al
+00000222  0000              add [rax],al
+00000224  0000              add [rax],al
+00000226  0000              add [rax],al
+00000228  0000              add [rax],al
+0000022A  0000              add [rax],al
+0000022C  0000              add [rax],al
+0000022E  0000              add [rax],al
+00000230  1000              adc [rax],al
+00000232  0000              add [rax],al
+00000234  0000              add [rax],al
+00000236  0000              add [rax],al
+00000238  0000              add [rax],al
+0000023A  0000              add [rax],al
+0000023C  0000              add [rax],al
+0000023E  0000              add [rax],al
+00000240  16                db 0x16
+00000241  0000              add [rax],al
+00000243  0001              add [rcx],al
+00000245  0000              add [rax],al
+00000247  0000              add [rax],al
+00000249  0000              add [rax],al
+0000024B  0000              add [rax],al
+0000024D  0000              add [rax],al
+0000024F  0000              add [rax],al
+00000251  0000              add [rax],al
+00000253  0000              add [rax],al
+00000255  0000              add [rax],al
+00000257  006000            add [rax+0x0],ah
+0000025A  0000              add [rax],al
+0000025C  0000              add [rax],al
+0000025E  0000              add [rax],al
+00000260  0000              add [rax],al
+00000262  0000              add [rax],al
+00000264  0000              add [rax],al
+00000266  0000              add [rax],al
+00000268  0000              add [rax],al
+0000026A  0000              add [rax],al
+0000026C  0000              add [rax],al
+0000026E  0000              add [rax],al
+00000270  0100              add [rax],eax
+00000272  0000              add [rax],al
+00000274  0000              add [rax],al
+00000276  0000              add [rax],al
+00000278  0000              add [rax],al
+0000027A  0000              add [rax],al
+0000027C  0000              add [rax],al
+0000027E  0000              add [rax],al
+00000280  2B00              sub eax,[rax]
+00000282  0000              add [rax],al
+00000284  0100              add [rax],eax
+00000286  007002            add [rax+0x2],dh
+00000289  0000              add [rax],al
+0000028B  0000              add [rax],al
+0000028D  0000              add [rax],al
+0000028F  0000              add [rax],al
+00000291  0000              add [rax],al
+00000293  0000              add [rax],al
+00000295  0000              add [rax],al
+00000297  006000            add [rax+0x0],ah
+0000029A  0000              add [rax],al
+0000029C  0000              add [rax],al
+0000029E  0000              add [rax],al
+000002A0  480000            o64 add [rax],al
+000002A3  0000              add [rax],al
+000002A5  0000              add [rax],al
+000002A7  0000              add [rax],al
+000002A9  0000              add [rax],al
+000002AB  0000              add [rax],al
+000002AD  0000              add [rax],al
+000002AF  0008              add [rax],cl
+000002B1  0000              add [rax],al
+000002B3  0000              add [rax],al
+000002B5  0000              add [rax],al
+000002B7  0000              add [rax],al
+000002B9  0000              add [rax],al
+000002BB  0000              add [rax],al
+000002BD  0000              add [rax],al
+000002BF  0026              add [rsi],ah
+000002C1  0000              add [rax],al
+000002C3  000400            add [rax+rax],al
+000002C6  0000              add [rax],al
+000002C8  0000              add [rax],al
+000002CA  0000              add [rax],al
+000002CC  0000              add [rax],al
+000002CE  0000              add [rax],al
+000002D0  0000              add [rax],al
+000002D2  0000              add [rax],al
+000002D4  0000              add [rax],al
+000002D6  0000              add [rax],al
+000002D8  0801              or [rcx],al
+000002DA  0000              add [rax],al
+000002DC  0000              add [rax],al
+000002DE  0000              add [rax],al
+000002E0  3000              xor [rax],al
+000002E2  0000              add [rax],al
+000002E4  0000              add [rax],al
+000002E6  0000              add [rax],al
+000002E8  06                db 0x06
+000002E9  0000              add [rax],al
+000002EB  000400            add [rax+rax],al
+000002EE  0000              add [rax],al
+000002F0  0800              or [rax],al
+000002F2  0000              add [rax],al
+000002F4  0000              add [rax],al
+000002F6  0000              add [rax],al
+000002F8  1800              sbb [rax],al
+000002FA  0000              add [rax],al
+000002FC  0000              add [rax],al
+000002FE  0000              add [rax],al
+00000300  3D00000002        cmp eax,0x2000000
+00000305  0000              add [rax],al
+00000307  0000              add [rax],al
+00000309  0000              add [rax],al
+0000030B  0000              add [rax],al
+0000030D  0000              add [rax],al
+0000030F  0000              add [rax],al
+00000311  0000              add [rax],al
+00000313  0000              add [rax],al
+00000315  0000              add [rax],al
+00000317  00A800000000      add [rax+0x0],ch
+0000031D  0000              add [rax],al
+0000031F  006000            add [rax+0x0],ah
+00000322  0000              add [rax],al
+00000324  0000              add [rax],al
+00000326  0000              add [rax],al
+00000328  0100              add [rax],eax
+0000032A  0000              add [rax],al
+0000032C  0300              add eax,[rax]
+0000032E  0000              add [rax],al
+00000330  0800              or [rax],al
+00000332  0000              add [rax],al
+00000334  0000              add [rax],al
+00000336  0000              add [rax],al
+00000338  1800              sbb [rax],al
+0000033A  0000              add [rax],al
+0000033C  0000              add [rax],al
+0000033E  0000              add [rax],al
diff --git a/out2.o b/out2.o
new file mode 100644
index 0000000000..d34ace88dd
Binary files /dev/null and b/out2.o differ
diff --git a/rust b/rust
new file mode 100755
index 0000000000..cde50d8fdf
Binary files /dev/null and b/rust differ
diff --git a/rust.rs b/rust.rs
new file mode 100644
index 0000000000..cd1dc619e8
--- /dev/null
+++ b/rust.rs
@@ -0,0 +1,13 @@
+pub fn foo(x: i64) -> (i64, i64) {
+    return (x, x);
+}
+
+pub fn test_main() -> i64 {
+    let record = foo(0x9);
+
+    record.0 * record.1
+}
+
+pub fn main() {
+    test_main();
+}
diff --git a/rust.s b/rust.s
new file mode 100644
index 0000000000..f70c1dc0fb
--- /dev/null
+++ b/rust.s
@@ -0,0 +1,315 @@
+	.text
+	.file	"rust.7rcbfp3g-cgu.0"
+	.section	.text._ZN3std2rt10lang_start17h10ea254a893e0692E,"ax",@progbits
+	.hidden	_ZN3std2rt10lang_start17h10ea254a893e0692E
+	.globl	_ZN3std2rt10lang_start17h10ea254a893e0692E
+	.p2align	4, 0x90
+	.type	_ZN3std2rt10lang_start17h10ea254a893e0692E,@function
+_ZN3std2rt10lang_start17h10ea254a893e0692E:
+	.cfi_startproc
+	subq	$40, %rsp
+	.cfi_def_cfa_offset 48
+	leaq	.L__unnamed_1(%rip), %rax
+	movq	%rdi, 32(%rsp)
+	leaq	32(%rsp), %rcx
+	movq	%rcx, %rdi
+	movq	%rsi, 24(%rsp)
+	movq	%rax, %rsi
+	movq	24(%rsp), %rax
+	movq	%rdx, 16(%rsp)
+	movq	%rax, %rdx
+	movq	16(%rsp), %rcx
+	callq	*_ZN3std2rt19lang_start_internal17h9cf8802361ad86c2E@GOTPCREL(%rip)
+	movq	%rax, 8(%rsp)
+	movq	8(%rsp), %rax
+	addq	$40, %rsp
+	.cfi_def_cfa_offset 8
+	retq
+.Lfunc_end0:
+	.size	_ZN3std2rt10lang_start17h10ea254a893e0692E, .Lfunc_end0-_ZN3std2rt10lang_start17h10ea254a893e0692E
+	.cfi_endproc
+
+	.section	".text._ZN3std2rt10lang_start28_$u7b$$u7b$closure$u7d$$u7d$17haa4f2d7d298b0acfE","ax",@progbits
+	.p2align	4, 0x90
+	.type	_ZN3std2rt10lang_start28_$u7b$$u7b$closure$u7d$$u7d$17haa4f2d7d298b0acfE,@function
+_ZN3std2rt10lang_start28_$u7b$$u7b$closure$u7d$$u7d$17haa4f2d7d298b0acfE:
+	.cfi_startproc
+	pushq	%rax
+	.cfi_def_cfa_offset 16
+	callq	*(%rdi)
+	callq	_ZN54_$LT$$LP$$RP$$u20$as$u20$std..process..Termination$GT$6report17h4c1d7168636eac2bE
+	movl	%eax, 4(%rsp)
+	movl	4(%rsp), %eax
+	popq	%rcx
+	.cfi_def_cfa_offset 8
+	retq
+.Lfunc_end1:
+	.size	_ZN3std2rt10lang_start28_$u7b$$u7b$closure$u7d$$u7d$17haa4f2d7d298b0acfE, .Lfunc_end1-_ZN3std2rt10lang_start28_$u7b$$u7b$closure$u7d$$u7d$17haa4f2d7d298b0acfE
+	.cfi_endproc
+
+	.section	.text._ZN3std3sys4unix7process14process_common8ExitCode6as_i3217hafc7a17b3af818e6E,"ax",@progbits
+	.p2align	4, 0x90
+	.type	_ZN3std3sys4unix7process14process_common8ExitCode6as_i3217hafc7a17b3af818e6E,@function
+_ZN3std3sys4unix7process14process_common8ExitCode6as_i3217hafc7a17b3af818e6E:
+	.cfi_startproc
+	movzbl	(%rdi), %eax
+	retq
+.Lfunc_end2:
+	.size	_ZN3std3sys4unix7process14process_common8ExitCode6as_i3217hafc7a17b3af818e6E, .Lfunc_end2-_ZN3std3sys4unix7process14process_common8ExitCode6as_i3217hafc7a17b3af818e6E
+	.cfi_endproc
+
+	.section	".text._ZN4core3ops8function6FnOnce40call_once$u7b$$u7b$vtable.shim$u7d$$u7d$17h3c0881b3435f345aE","ax",@progbits
+	.p2align	4, 0x90
+	.type	_ZN4core3ops8function6FnOnce40call_once$u7b$$u7b$vtable.shim$u7d$$u7d$17h3c0881b3435f345aE,@function
+_ZN4core3ops8function6FnOnce40call_once$u7b$$u7b$vtable.shim$u7d$$u7d$17h3c0881b3435f345aE:
+	.cfi_startproc
+	subq	$24, %rsp
+	.cfi_def_cfa_offset 32
+	movq	(%rdi), %rdi
+	callq	_ZN4core3ops8function6FnOnce9call_once17h95777eb19c893e7cE
+	movl	%eax, 12(%rsp)
+	movl	12(%rsp), %eax
+	addq	$24, %rsp
+	.cfi_def_cfa_offset 8
+	retq
+.Lfunc_end3:
+	.size	_ZN4core3ops8function6FnOnce40call_once$u7b$$u7b$vtable.shim$u7d$$u7d$17h3c0881b3435f345aE, .Lfunc_end3-_ZN4core3ops8function6FnOnce40call_once$u7b$$u7b$vtable.shim$u7d$$u7d$17h3c0881b3435f345aE
+	.cfi_endproc
+
+	.section	.text._ZN4core3ops8function6FnOnce9call_once17h95777eb19c893e7cE,"ax",@progbits
+	.p2align	4, 0x90
+	.type	_ZN4core3ops8function6FnOnce9call_once17h95777eb19c893e7cE,@function
+_ZN4core3ops8function6FnOnce9call_once17h95777eb19c893e7cE:
+.Lfunc_begin0:
+	.cfi_startproc
+	.cfi_personality 155, DW.ref.rust_eh_personality
+	.cfi_lsda 27, .Lexception0
+	subq	$40, %rsp
+	.cfi_def_cfa_offset 48
+	movq	%rdi, 8(%rsp)
+.Ltmp0:
+	leaq	8(%rsp), %rdi
+	callq	_ZN3std2rt10lang_start28_$u7b$$u7b$closure$u7d$$u7d$17haa4f2d7d298b0acfE
+.Ltmp1:
+	movl	%eax, 4(%rsp)
+	jmp	.LBB4_1
+.LBB4_1:
+	jmp	.LBB4_2
+.LBB4_2:
+	movl	4(%rsp), %eax
+	addq	$40, %rsp
+	.cfi_def_cfa_offset 8
+	retq
+.LBB4_3:
+	.cfi_def_cfa_offset 48
+	jmp	.LBB4_4
+.LBB4_4:
+	movq	24(%rsp), %rdi
+	callq	_Unwind_Resume@PLT
+	ud2
+.LBB4_5:
+.Ltmp2:
+	movq	%rax, 24(%rsp)
+	movl	%edx, 32(%rsp)
+	jmp	.LBB4_3
+.Lfunc_end4:
+	.size	_ZN4core3ops8function6FnOnce9call_once17h95777eb19c893e7cE, .Lfunc_end4-_ZN4core3ops8function6FnOnce9call_once17h95777eb19c893e7cE
+	.cfi_endproc
+	.section	.gcc_except_table,"a",@progbits
+	.p2align	2
+GCC_except_table4:
+.Lexception0:
+	.byte	255
+	.byte	255
+	.byte	1
+	.uleb128 .Lcst_end0-.Lcst_begin0
+.Lcst_begin0:
+	.uleb128 .Ltmp0-.Lfunc_begin0
+	.uleb128 .Ltmp1-.Ltmp0
+	.uleb128 .Ltmp2-.Lfunc_begin0
+	.byte	0
+	.uleb128 .Ltmp1-.Lfunc_begin0
+	.uleb128 .Lfunc_end4-.Ltmp1
+	.byte	0
+	.byte	0
+.Lcst_end0:
+	.p2align	2
+
+	.section	.text._ZN4core3ptr13drop_in_place17h5ea43678993f7f74E,"ax",@progbits
+	.p2align	4, 0x90
+	.type	_ZN4core3ptr13drop_in_place17h5ea43678993f7f74E,@function
+_ZN4core3ptr13drop_in_place17h5ea43678993f7f74E:
+	.cfi_startproc
+	retq
+.Lfunc_end5:
+	.size	_ZN4core3ptr13drop_in_place17h5ea43678993f7f74E, .Lfunc_end5-_ZN4core3ptr13drop_in_place17h5ea43678993f7f74E
+	.cfi_endproc
+
+	.section	".text._ZN54_$LT$$LP$$RP$$u20$as$u20$std..process..Termination$GT$6report17h4c1d7168636eac2bE","ax",@progbits
+	.p2align	4, 0x90
+	.type	_ZN54_$LT$$LP$$RP$$u20$as$u20$std..process..Termination$GT$6report17h4c1d7168636eac2bE,@function
+_ZN54_$LT$$LP$$RP$$u20$as$u20$std..process..Termination$GT$6report17h4c1d7168636eac2bE:
+	.cfi_startproc
+	pushq	%rax
+	.cfi_def_cfa_offset 16
+	xorl	%edi, %edi
+	callq	_ZN68_$LT$std..process..ExitCode$u20$as$u20$std..process..Termination$GT$6report17h4641d8c7c31fa834E
+	movl	%eax, 4(%rsp)
+	movl	4(%rsp), %eax
+	popq	%rcx
+	.cfi_def_cfa_offset 8
+	retq
+.Lfunc_end6:
+	.size	_ZN54_$LT$$LP$$RP$$u20$as$u20$std..process..Termination$GT$6report17h4c1d7168636eac2bE, .Lfunc_end6-_ZN54_$LT$$LP$$RP$$u20$as$u20$std..process..Termination$GT$6report17h4c1d7168636eac2bE
+	.cfi_endproc
+
+	.section	".text._ZN68_$LT$std..process..ExitCode$u20$as$u20$std..process..Termination$GT$6report17h4641d8c7c31fa834E","ax",@progbits
+	.p2align	4, 0x90
+	.type	_ZN68_$LT$std..process..ExitCode$u20$as$u20$std..process..Termination$GT$6report17h4641d8c7c31fa834E,@function
+_ZN68_$LT$std..process..ExitCode$u20$as$u20$std..process..Termination$GT$6report17h4641d8c7c31fa834E:
+	.cfi_startproc
+	pushq	%rax
+	.cfi_def_cfa_offset 16
+	movb	%dil, 7(%rsp)
+	leaq	7(%rsp), %rdi
+	callq	_ZN3std3sys4unix7process14process_common8ExitCode6as_i3217hafc7a17b3af818e6E
+	movl	%eax, (%rsp)
+	movl	(%rsp), %eax
+	popq	%rcx
+	.cfi_def_cfa_offset 8
+	retq
+.Lfunc_end7:
+	.size	_ZN68_$LT$std..process..ExitCode$u20$as$u20$std..process..Termination$GT$6report17h4641d8c7c31fa834E, .Lfunc_end7-_ZN68_$LT$std..process..ExitCode$u20$as$u20$std..process..Termination$GT$6report17h4641d8c7c31fa834E
+	.cfi_endproc
+
+	.section	.text._ZN4rust3foo17h24346e1203f74a2dE,"ax",@progbits
+	.p2align	4, 0x90
+	.type	_ZN4rust3foo17h24346e1203f74a2dE,@function
+_ZN4rust3foo17h24346e1203f74a2dE:
+	.cfi_startproc
+	subq	$16, %rsp
+	.cfi_def_cfa_offset 24
+	movq	%rdi, (%rsp)
+	movq	%rdi, 8(%rsp)
+	movq	(%rsp), %rax
+	movq	8(%rsp), %rdx
+	addq	$16, %rsp
+	.cfi_def_cfa_offset 8
+	retq
+.Lfunc_end8:
+	.size	_ZN4rust3foo17h24346e1203f74a2dE, .Lfunc_end8-_ZN4rust3foo17h24346e1203f74a2dE
+	.cfi_endproc
+
+	.section	.text._ZN4rust9test_main17h45325f9e1ca54b4bE,"ax",@progbits
+	.p2align	4, 0x90
+	.type	_ZN4rust9test_main17h45325f9e1ca54b4bE,@function
+_ZN4rust9test_main17h45325f9e1ca54b4bE:
+	.cfi_startproc
+	subq	$24, %rsp
+	.cfi_def_cfa_offset 32
+	movl	$9, %edi
+	callq	_ZN4rust3foo17h24346e1203f74a2dE
+	movq	%rax, 16(%rsp)
+	movq	%rdx, 8(%rsp)
+	movq	16(%rsp), %rax
+	movq	8(%rsp), %rcx
+	imulq	%rcx, %rax
+	seto	%dl
+	testb	$1, %dl
+	movq	%rax, (%rsp)
+	jne	.LBB9_3
+	movq	(%rsp), %rax
+	addq	$24, %rsp
+	.cfi_def_cfa_offset 8
+	retq
+.LBB9_3:
+	.cfi_def_cfa_offset 32
+	leaq	str.0(%rip), %rdi
+	leaq	.L__unnamed_2(%rip), %rdx
+	movq	_ZN4core9panicking5panic17hcdc9f0ba8d71d265E@GOTPCREL(%rip), %rax
+	movl	$33, %esi
+	callq	*%rax
+	ud2
+.Lfunc_end9:
+	.size	_ZN4rust9test_main17h45325f9e1ca54b4bE, .Lfunc_end9-_ZN4rust9test_main17h45325f9e1ca54b4bE
+	.cfi_endproc
+
+	.section	.text._ZN4rust4main17h523dcf5432fcfd88E,"ax",@progbits
+	.p2align	4, 0x90
+	.type	_ZN4rust4main17h523dcf5432fcfd88E,@function
+_ZN4rust4main17h523dcf5432fcfd88E:
+	.cfi_startproc
+	pushq	%rax
+	.cfi_def_cfa_offset 16
+	callq	_ZN4rust9test_main17h45325f9e1ca54b4bE
+	popq	%rax
+	.cfi_def_cfa_offset 8
+	retq
+.Lfunc_end10:
+	.size	_ZN4rust4main17h523dcf5432fcfd88E, .Lfunc_end10-_ZN4rust4main17h523dcf5432fcfd88E
+	.cfi_endproc
+
+	.section	.text.main,"ax",@progbits
+	.globl	main
+	.p2align	4, 0x90
+	.type	main,@function
+main:
+	.cfi_startproc
+	pushq	%rax
+	.cfi_def_cfa_offset 16
+	movslq	%edi, %rax
+	leaq	_ZN4rust4main17h523dcf5432fcfd88E(%rip), %rdi
+	movq	%rsi, (%rsp)
+	movq	%rax, %rsi
+	movq	(%rsp), %rdx
+	callq	_ZN3std2rt10lang_start17h10ea254a893e0692E
+	popq	%rcx
+	.cfi_def_cfa_offset 8
+	retq
+.Lfunc_end11:
+	.size	main, .Lfunc_end11-main
+	.cfi_endproc
+
+	.type	.L__unnamed_1,@object
+	.section	.data.rel.ro..L__unnamed_1,"aw",@progbits
+	.p2align	3
+.L__unnamed_1:
+	.quad	_ZN4core3ptr13drop_in_place17h5ea43678993f7f74E
+	.quad	8
+	.quad	8
+	.quad	_ZN3std2rt10lang_start28_$u7b$$u7b$closure$u7d$$u7d$17haa4f2d7d298b0acfE
+	.quad	_ZN3std2rt10lang_start28_$u7b$$u7b$closure$u7d$$u7d$17haa4f2d7d298b0acfE
+	.quad	_ZN4core3ops8function6FnOnce40call_once$u7b$$u7b$vtable.shim$u7d$$u7d$17h3c0881b3435f345aE
+	.size	.L__unnamed_1, 48
+
+	.type	.L__unnamed_3,@object
+	.section	.rodata..L__unnamed_3,"a",@progbits
+.L__unnamed_3:
+	.ascii	"rust.rs"
+	.size	.L__unnamed_3, 7
+
+	.type	.L__unnamed_2,@object
+	.section	.data.rel.ro..L__unnamed_2,"aw",@progbits
+	.p2align	3
+.L__unnamed_2:
+	.quad	.L__unnamed_3
+	.asciz	"\007\000\000\000\000\000\000\000\b\000\000\000\005\000\000"
+	.size	.L__unnamed_2, 24
+
+	.type	str.0,@object
+	.section	.rodata.str.0,"a",@progbits
+	.p2align	4
+str.0:
+	.ascii	"attempt to multiply with overflow"
+	.size	str.0, 33
+
+	.hidden	DW.ref.rust_eh_personality
+	.weak	DW.ref.rust_eh_personality
+	.section	.data.DW.ref.rust_eh_personality,"aGw",@progbits,DW.ref.rust_eh_personality,comdat
+	.p2align	3
+	.type	DW.ref.rust_eh_personality,@object
+	.size	DW.ref.rust_eh_personality, 8
+DW.ref.rust_eh_personality:
+	.quad	rust_eh_personality
+
+	.section	".note.GNU-stack","",@progbits