get foreign call compiling (but not working)

compiler/gen/src/llvm/build.rs

@@ -810,6 +810,24 @@ pub fn build_exp_expr<'a, 'ctx, 'env>(
         Literal(literal) => build_exp_literal(env, literal),
         RunLowLevel(op, symbols) => run_low_level(env, scope, parent, layout, *op, symbols),
 
+        ForeignCall(foreign_symbol, symbols) => {
+            let function = get_foreign_symbol(env, foreign_symbol.clone());
+
+            let mut arg_vals: Vec<BasicValueEnum> = Vec::with_capacity_in(symbols.len(), env.arena);
+
+            for arg in symbols.iter() {
+                arg_vals.push(load_symbol(env, scope, arg));
+            }
+
+            let call = env.builder.build_call(function, arg_vals.as_slice(), "tmp");
+
+            // this is a foreign function, use c calling convention
+            call.set_call_convention(C_CALL_CONV);
+
+            call.try_as_basic_value()
+                .left()
+                .unwrap_or_else(|| panic!("LLVM error: Invalid call by pointer."))
+        }
         FunctionCall {
             call_type: ByName(name),
             full_layout,
@@ -3402,6 +3420,28 @@ fn cxa_rethrow_exception<'a, 'ctx, 'env>(env: &Env<'a, 'ctx, 'env>) -> BasicValu
     call.try_as_basic_value().left().unwrap()
 }
 
+fn get_foreign_symbol<'a, 'ctx, 'env>(
+    env: &Env<'a, 'ctx, 'env>,
+    foreign_symbol: roc_module::ident::ForeignSymbol,
+) -> FunctionValue<'ctx> {
+    let module = env.module;
+    let context = env.context;
+
+    match module.get_function(foreign_symbol.as_str()) {
+        Some(gvalue) => gvalue,
+        None => {
+            let foreign_function = module.add_function(
+                foreign_symbol.as_str(),
+                context.i64_type().fn_type(&[], false),
+                Some(Linkage::External),
+            );
+            foreign_function.set_call_conventions(C_CALL_CONV);
+
+            foreign_function
+        }
+    }
+}
+
 fn get_gxx_personality_v0<'a, 'ctx, 'env>(env: &Env<'a, 'ctx, 'env>) -> FunctionValue<'ctx> {
     let name = "__gxx_personality_v0";
 

compiler/load/src/file.rs

@@ -2146,9 +2146,8 @@ fn fabricate_host_exposed_def<'a>(
     }
 
     // TODO figure out something better for run lowlevel
-    use roc_module::low_level::LowLevel;
-    let low_level_call = Expr::RunLowLevel {
-        op: LowLevel::Not,
+    let low_level_call = Expr::ForeignCall {
+        foreign_symbol: "roc_fx_put_char".into(),
         args: linked_symbol_arguments,
         ret_var: var_store.fresh(),
     };

compiler/mono/src/ir.rs

@@ -3264,7 +3264,33 @@ pub fn with_hole<'a>(
             foreign_symbol,
             args,
             ret_var,
-        } => todo!(),
+        } => {
+            let mut arg_symbols = Vec::with_capacity_in(args.len(), env.arena);
+
+            for (_, arg_expr) in args.iter() {
+                arg_symbols.push(possible_reuse_symbol(env, procs, &arg_expr));
+            }
+            let arg_symbols = arg_symbols.into_bump_slice();
+
+            // layout of the return type
+            let layout = layout_cache
+                .from_var(env.arena, ret_var, env.subs)
+                .unwrap_or_else(|err| todo!("TODO turn fn_var into a RuntimeError {:?}", err));
+
+            let result = Stmt::Let(
+                assigned,
+                Expr::ForeignCall(foreign_symbol.clone(), arg_symbols),
+                layout,
+                hole,
+            );
+
+            let iter = args
+                .into_iter()
+                .rev()
+                .map(|(a, b)| (a, Located::at_zero(b)))
+                .zip(arg_symbols.iter().rev());
+            assign_to_symbols(env, procs, layout_cache, iter, result)
+        }
 
         RunLowLevel { op, args, ret_var } => {
             let op = optimize_low_level(env.subs, op, &args);