diff --git a/Cargo.lock b/Cargo.lock
index 9358a3163a..76cacfcbb6 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2569,6 +2569,7 @@ dependencies = [
  "roc_can",
  "roc_collections",
  "roc_constrain",
+ "roc_fmt",
  "roc_gen",
  "roc_load",
  "roc_module",
diff --git a/compiler/builtins/bitcode/src/helpers/grapheme.zig b/compiler/builtins/bitcode/src/helpers/grapheme.zig
index 2f1e75d3d6..252873cb4e 100644
--- a/compiler/builtins/bitcode/src/helpers/grapheme.zig
+++ b/compiler/builtins/bitcode/src/helpers/grapheme.zig
@@ -4,7 +4,7 @@ const expectEqual = std.testing.expectEqual;
 
 // This whole module is a translation of grapheme breaks from
 // the https://github.com/JuliaStrings/utf8proc library.
-// Thanks so much to those developer!
+// Thanks so much to those developers!
 //
 // The only function this file exposes is `isGraphemeBreak`
 //
diff --git a/compiler/builtins/bitcode/src/main.zig b/compiler/builtins/bitcode/src/main.zig
index 257bd9e52f..465d1c066e 100644
--- a/compiler/builtins/bitcode/src/main.zig
+++ b/compiler/builtins/bitcode/src/main.zig
@@ -21,18 +21,19 @@ comptime {
     exportStrFn(str.startsWith, "starts_with");
     exportStrFn(str.endsWith, "ends_with");
     exportStrFn(str.strConcat, "concat");
-    exportStrFn(str.strLen, "len");
+    exportStrFn(str.strNumberOfBytes, "number_of_bytes");
+    exportStrFn(str.strFromInt, "from_int");
 }
 
 // Export helpers - Must be run inside a comptime
-fn exportBuiltinFn(comptime fn_target: anytype, comptime fn_name: []const u8) void {
-    @export(fn_target, .{ .name = "roc_builtins." ++ fn_name, .linkage = .Strong });
+fn exportBuiltinFn(comptime func: anytype, comptime func_name: []const u8) void {
+    @export(func, .{ .name = "roc_builtins." ++ func_name, .linkage = .Strong });
 }
-fn exportNumFn(comptime fn_target: anytype, comptime fn_name: []const u8) void {
-    exportBuiltinFn(fn_target, "num." ++ fn_name);
+fn exportNumFn(comptime func: anytype, comptime func_name: []const u8) void {
+    exportBuiltinFn(func, "num." ++ func_name);
 }
-fn exportStrFn(comptime fn_target: anytype, comptime fn_name: []const u8) void {
-    exportBuiltinFn(fn_target, "str." ++ fn_name);
+fn exportStrFn(comptime func: anytype, comptime func_name: []const u8) void {
+    exportBuiltinFn(func, "str." ++ func_name);
 }
 
 // Run all tests in imported modules
diff --git a/compiler/builtins/bitcode/src/str.zig b/compiler/builtins/bitcode/src/str.zig
index 39281d1b33..f7b2c2ba4c 100644
--- a/compiler/builtins/bitcode/src/str.zig
+++ b/compiler/builtins/bitcode/src/str.zig
@@ -21,16 +21,16 @@ const RocStr = extern struct {
     // This takes ownership of the pointed-to bytes if they won't fit in a
     // small string, and returns a (pointer, len) tuple which points to them.
     pub fn init(bytes: [*]const u8, length: usize) RocStr {
-        const rocStrSize = @sizeOf(RocStr);
+        const roc_str_size = @sizeOf(RocStr);
 
-        if (length < rocStrSize) {
+        if (length < roc_str_size) {
             var ret_small_str = RocStr.empty();
             const target_ptr = @ptrToInt(&ret_small_str);
             var index: u8 = 0;
 
             // TODO isn't there a way to bulk-zero data in Zig?
             // Zero out the data, just to be safe
-            while (index < rocStrSize) {
+            while (index < roc_str_size) {
                 var offset_ptr = @intToPtr(*u8, target_ptr + index);
                 offset_ptr.* = 0;
                 index += 1;
@@ -45,14 +45,28 @@ const RocStr = extern struct {
             }
 
             // set the final byte to be the length
-            const final_byte_ptr = @intToPtr(*u8, target_ptr + rocStrSize - 1);
+            const final_byte_ptr = @intToPtr(*u8, target_ptr + roc_str_size - 1);
             final_byte_ptr.* = @truncate(u8, length) ^ 0b10000000;
 
             return ret_small_str;
         } else {
-            var new_bytes: [*]u8 = @ptrCast([*]u8, malloc(length));
+            var result = allocateStr(u64, InPlace.Clone, length);
 
-            @memcpy(new_bytes, bytes, length);
+            @memcpy(@ptrCast([*]u8, result.str_bytes), bytes, length);
+
+            return result;
+        }
+    }
+
+    // This takes ownership of the pointed-to bytes if they won't fit in a
+    // small string, and returns a (pointer, len) tuple which points to them.
+    pub fn withCapacity(length: usize) RocStr {
+        const roc_str_size = @sizeOf(RocStr);
+
+        if (length < roc_str_size) {
+            return RocStr.empty();
+        } else {
+            var new_bytes: [*]u8 = @ptrCast([*]u8, malloc(length));
 
             return RocStr{
                 .str_bytes = new_bytes,
@@ -61,8 +75,8 @@ const RocStr = extern struct {
         }
     }
 
-    pub fn drop(self: RocStr) void {
-        if (!self.is_small_str()) {
+    pub fn deinit(self: RocStr) void {
+        if (!self.isSmallStr()) {
             const str_bytes: [*]u8 = self.str_bytes orelse unreachable;
 
             free(str_bytes);
@@ -88,13 +102,14 @@ const RocStr = extern struct {
 
         const self_u8_ptr: [*]const u8 = @ptrCast([*]const u8, &self);
         const other_u8_ptr: [*]const u8 = @ptrCast([*]const u8, &other);
-        const self_bytes: [*]const u8 = if (self.is_small_str() or self.is_empty()) self_u8_ptr else self_bytes_ptr orelse unreachable;
-        const other_bytes: [*]const u8 = if (other.is_small_str() or other.is_empty()) other_u8_ptr else other_bytes_ptr orelse unreachable;
+        const self_bytes: [*]const u8 = if (self.isSmallStr() or self.isEmpty()) self_u8_ptr else self_bytes_ptr orelse unreachable;
+        const other_bytes: [*]const u8 = if (other.isSmallStr() or other.isEmpty()) other_u8_ptr else other_bytes_ptr orelse unreachable;
 
         var index: usize = 0;
 
         // TODO rewrite this into a for loop
-        while (index < self.len()) {
+        const length = self.len();
+        while (index < length) {
             if (self_bytes[index] != other_bytes[index]) {
                 return false;
             }
@@ -105,7 +120,7 @@ const RocStr = extern struct {
         return true;
     }
 
-    pub fn is_small_str(self: RocStr) bool {
+    pub fn isSmallStr(self: RocStr) bool {
         return @bitCast(isize, self.str_len) < 0;
     }
 
@@ -117,17 +132,17 @@ const RocStr = extern struct {
 
         // Since this conditional would be prone to branch misprediction,
         // make sure it will compile to a cmov.
-        return if (self.is_small_str()) small_len else big_len;
+        return if (self.isSmallStr()) small_len else big_len;
     }
 
-    pub fn is_empty(self: RocStr) bool {
+    pub fn isEmpty(self: RocStr) bool {
         return self.len() == 0;
     }
 
-    pub fn as_u8_ptr(self: RocStr) [*]u8 {
+    pub fn asU8ptr(self: RocStr) [*]u8 {
         const if_small = &@bitCast([16]u8, self);
         const if_big = @ptrCast([*]u8, self.str_bytes);
-        return if (self.is_small_str() or self.is_empty()) if_small else if_big;
+        return if (self.isSmallStr() or self.isEmpty()) if_small else if_big;
     }
 
     // Given a pointer to some bytes, write the first (len) bytes of this
@@ -145,7 +160,7 @@ const RocStr = extern struct {
 
         // Since this conditional would be prone to branch misprediction,
         // make sure it will compile to a cmov.
-        const src: [*]u8 = if (self.is_small_str()) small_src else big_src;
+        const src: [*]u8 = if (self.isSmallStr()) small_src else big_src;
 
         @memcpy(dest, src, len);
     }
@@ -164,8 +179,8 @@ const RocStr = extern struct {
         // TODO: fix those tests
         // expect(roc_str1.eq(roc_str2));
 
-        roc_str1.drop();
-        roc_str2.drop();
+        roc_str1.deinit();
+        roc_str2.deinit();
     }
 
     test "RocStr.eq: not equal different length" {
@@ -181,8 +196,8 @@ const RocStr = extern struct {
 
         expect(!roc_str1.eq(roc_str2));
 
-        roc_str1.drop();
-        roc_str2.drop();
+        roc_str1.deinit();
+        roc_str2.deinit();
     }
 
     test "RocStr.eq: not equal same length" {
@@ -199,17 +214,39 @@ const RocStr = extern struct {
         // TODO: fix those tests
         // expect(!roc_str1.eq(roc_str2));
 
-        roc_str1.drop();
-        roc_str2.drop();
+        roc_str1.deinit();
+        roc_str2.deinit();
     }
 };
 
 // Str.numberOfBytes
 
-pub fn strLen(string: RocStr) callconv(.C) u64 {
+pub fn strNumberOfBytes(string: RocStr) callconv(.C) usize {
     return string.len();
 }
 
+// Str.fromInt
+
+pub fn strFromInt(int: i64) callconv(.C) RocStr {
+    // prepare for having multiple integer types in the future
+    return strFromIntHelp(i64, int);
+}
+
+fn strFromIntHelp(comptime T: type, int: T) RocStr {
+    // determine maximum size for this T
+    comptime const size = comptime blk: {
+        // the string representation of the minimum i128 value uses at most 40 characters
+        var buf: [40]u8 = undefined;
+        var result = std.fmt.bufPrint(&buf, "{}", .{std.math.minInt(T)}) catch unreachable;
+        break :blk result.len;
+    };
+
+    var buf: [size]u8 = undefined;
+    const result = std.fmt.bufPrint(&buf, "{}", .{int}) catch unreachable;
+
+    return RocStr.init(&buf, result.len);
+}
+
 // Str.split
 
 pub fn strSplitInPlace(array: [*]RocStr, array_len: usize, string: RocStr, delimiter: RocStr) callconv(.C) void {
@@ -217,10 +254,10 @@ pub fn strSplitInPlace(array: [*]RocStr, array_len: usize, string: RocStr, delim
     var sliceStart_index: usize = 0;
     var str_index: usize = 0;
 
-    const str_bytes = string.as_u8_ptr();
+    const str_bytes = string.asU8ptr();
     const str_len = string.len();
 
-    const delimiter_bytes_ptrs = delimiter.as_u8_ptr();
+    const delimiter_bytes_ptrs = delimiter.asU8ptr();
     const delimiter_len = delimiter.len();
 
     if (str_len > delimiter_len) {
@@ -278,11 +315,11 @@ test "strSplitInPlace: no delimiter" {
     expect(array[0].eq(expected[0]));
 
     for (array) |roc_str| {
-        roc_str.drop();
+        roc_str.deinit();
     }
 
     for (expected) |roc_str| {
-        roc_str.drop();
+        roc_str.deinit();
     }
 }
 
@@ -378,10 +415,10 @@ test "strSplitInPlace: three pieces" {
 // needs to be broken into, so that we can allocate a array
 // of that size. It always returns at least 1.
 pub fn countSegments(string: RocStr, delimiter: RocStr) callconv(.C) usize {
-    const str_bytes = string.as_u8_ptr();
+    const str_bytes = string.asU8ptr();
     const str_len = string.len();
 
-    const delimiter_bytes_ptrs = delimiter.as_u8_ptr();
+    const delimiter_bytes_ptrs = delimiter.asU8ptr();
     const delimiter_len = delimiter.len();
 
     var count: usize = 1;
@@ -464,12 +501,12 @@ test "countSegments: delimiter interspered" {
 const grapheme = @import("helpers/grapheme.zig");
 
 pub fn countGraphemeClusters(string: RocStr) callconv(.C) usize {
-    if (string.is_empty()) {
+    if (string.isEmpty()) {
         return 0;
     }
 
     const bytes_len = string.len();
-    const bytes_ptr = string.as_u8_ptr();
+    const bytes_ptr = string.asU8ptr();
 
     var bytes = bytes_ptr[0..bytes_len];
     var iter = (unicode.Utf8View.init(bytes) catch unreachable).iterator();
@@ -498,7 +535,7 @@ pub fn countGraphemeClusters(string: RocStr) callconv(.C) usize {
     return count;
 }
 
-fn roc_str_from_literal(bytes_arr: *const []u8) RocStr {}
+fn rocStrFromLiteral(bytes_arr: *const []u8) RocStr {}
 
 test "countGraphemeClusters: empty string" {
     const count = countGraphemeClusters(RocStr.empty());
@@ -544,10 +581,10 @@ test "countGraphemeClusters: emojis, ut8, and ascii characters" {
 
 pub fn startsWith(string: RocStr, prefix: RocStr) callconv(.C) bool {
     const bytes_len = string.len();
-    const bytes_ptr = string.as_u8_ptr();
+    const bytes_ptr = string.asU8ptr();
 
     const prefix_len = prefix.len();
-    const prefix_ptr = prefix.as_u8_ptr();
+    const prefix_ptr = prefix.asU8ptr();
 
     if (prefix_len > bytes_len) {
         return false;
@@ -586,10 +623,10 @@ test "startsWith: 12345678912345678910 starts with 123456789123456789" {
 
 pub fn endsWith(string: RocStr, suffix: RocStr) callconv(.C) bool {
     const bytes_len = string.len();
-    const bytes_ptr = string.as_u8_ptr();
+    const bytes_ptr = string.asU8ptr();
 
     const suffix_len = suffix.len();
-    const suffix_ptr = suffix.as_u8_ptr();
+    const suffix_ptr = suffix.asU8ptr();
 
     if (suffix_len > bytes_len) {
         return false;
@@ -653,10 +690,10 @@ test "RocStr.concat: small concat small" {
 
     expect(roc_str3.eq(result));
 
-    roc_str1.drop();
-    roc_str2.drop();
-    roc_str3.drop();
-    result.drop();
+    roc_str1.deinit();
+    roc_str2.deinit();
+    roc_str3.deinit();
+    result.deinit();
 }
 
 pub fn strConcat(ptr_size: u32, result_in_place: InPlace, arg1: RocStr, arg2: RocStr) callconv(.C) RocStr {
@@ -668,10 +705,10 @@ pub fn strConcat(ptr_size: u32, result_in_place: InPlace, arg1: RocStr, arg2: Ro
 }
 
 fn strConcatHelp(comptime T: type, result_in_place: InPlace, arg1: RocStr, arg2: RocStr) RocStr {
-    if (arg1.is_empty()) {
-        return cloneNonemptyStr(T, result_in_place, arg2);
-    } else if (arg2.is_empty()) {
-        return cloneNonemptyStr(T, result_in_place, arg1);
+    if (arg1.isEmpty()) {
+        return cloneStr(T, result_in_place, arg2);
+    } else if (arg2.isEmpty()) {
+        return cloneStr(T, result_in_place, arg1);
     } else {
         const combined_length = arg1.len() + arg2.len();
 
@@ -679,12 +716,12 @@ fn strConcatHelp(comptime T: type, result_in_place: InPlace, arg1: RocStr, arg2:
         const result_is_big = combined_length >= small_str_bytes;
 
         if (result_is_big) {
-            var result = allocate_str(T, result_in_place, combined_length);
+            var result = allocateStr(T, result_in_place, combined_length);
 
             {
                 const old_if_small = &@bitCast([16]u8, arg1);
                 const old_if_big = @ptrCast([*]u8, arg1.str_bytes);
-                const old_bytes = if (arg1.is_small_str()) old_if_small else old_if_big;
+                const old_bytes = if (arg1.isSmallStr()) old_if_small else old_if_big;
 
                 const new_bytes: [*]u8 = @ptrCast([*]u8, result.str_bytes);
 
@@ -694,7 +731,7 @@ fn strConcatHelp(comptime T: type, result_in_place: InPlace, arg1: RocStr, arg2:
             {
                 const old_if_small = &@bitCast([16]u8, arg2);
                 const old_if_big = @ptrCast([*]u8, arg2.str_bytes);
-                const old_bytes = if (arg2.is_small_str()) old_if_small else old_if_big;
+                const old_bytes = if (arg2.isSmallStr()) old_if_small else old_if_big;
 
                 const new_bytes = @ptrCast([*]u8, result.str_bytes) + arg1.len();
 
@@ -738,12 +775,12 @@ const InPlace = packed enum(u8) {
     Clone,
 };
 
-fn cloneNonemptyStr(comptime T: type, in_place: InPlace, str: RocStr) RocStr {
-    if (str.is_small_str() or str.is_empty()) {
+fn cloneStr(comptime T: type, in_place: InPlace, str: RocStr) RocStr {
+    if (str.isSmallStr() or str.isEmpty()) {
         // just return the bytes
         return str;
     } else {
-        var new_str = allocate_str(T, in_place, str.str_len);
+        var new_str = allocateStr(T, in_place, str.str_len);
 
         var old_bytes: [*]u8 = @ptrCast([*]u8, str.str_bytes);
         var new_bytes: [*]u8 = @ptrCast([*]u8, new_str.str_bytes);
@@ -754,7 +791,7 @@ fn cloneNonemptyStr(comptime T: type, in_place: InPlace, str: RocStr) RocStr {
     }
 }
 
-fn allocate_str(comptime T: type, in_place: InPlace, number_of_chars: u64) RocStr {
+fn allocateStr(comptime T: type, in_place: InPlace, number_of_chars: u64) RocStr {
     const length = @sizeOf(T) + number_of_chars;
     var new_bytes: [*]T = @ptrCast([*]T, @alignCast(@alignOf(T), malloc(length)));
 
@@ -765,7 +802,7 @@ fn allocate_str(comptime T: type, in_place: InPlace, number_of_chars: u64) RocSt
     }
 
     var first_element = @ptrCast([*]align(@alignOf(T)) u8, new_bytes);
-    first_element += 8;
+    first_element += @sizeOf(usize);
 
     return RocStr{
         .str_bytes = first_element,
diff --git a/compiler/builtins/src/bitcode.rs b/compiler/builtins/src/bitcode.rs
index 2fbd4f6782..5ccf0c89aa 100644
--- a/compiler/builtins/src/bitcode.rs
+++ b/compiler/builtins/src/bitcode.rs
@@ -29,4 +29,5 @@ pub const STR_STR_SPLIT_IN_PLACE: &str = "roc_builtins.str.str_split_in_place";
 pub const STR_COUNT_GRAPEHEME_CLUSTERS: &str = "roc_builtins.str.count_grapheme_clusters";
 pub const STR_STARTS_WITH: &str = "roc_builtins.str.starts_with";
 pub const STR_ENDS_WITH: &str = "roc_builtins.str.ends_with";
-pub const STR_LEN: &str = "roc_builtins.str.len";
+pub const STR_NUMBER_OF_BYTES: &str = "roc_builtins.str.number_of_bytes";
+pub const STR_FROM_INT: &str = "roc_builtins.str.from_int";
diff --git a/compiler/builtins/src/std.rs b/compiler/builtins/src/std.rs
index e6cd26405b..120e78dc58 100644
--- a/compiler/builtins/src/std.rs
+++ b/compiler/builtins/src/std.rs
@@ -429,6 +429,12 @@ pub fn types() -> MutMap<Symbol, (SolvedType, Region)> {
         top_level_function(vec![str_type()], Box::new(int_type())),
     );
 
+    // fromInt : Int -> Str
+    add_type(
+        Symbol::STR_FROM_INT,
+        top_level_function(vec![int_type()], Box::new(str_type())),
+    );
+
     // List module
 
     // get : List elem, Int -> Result elem [ OutOfBounds ]*
diff --git a/compiler/builtins/src/unique.rs b/compiler/builtins/src/unique.rs
index 45206d462e..406f4d313f 100644
--- a/compiler/builtins/src/unique.rs
+++ b/compiler/builtins/src/unique.rs
@@ -1108,6 +1108,12 @@ pub fn types() -> MutMap<Symbol, (SolvedType, Region)> {
         unique_function(vec![str_type(star1)], int_type(star2))
     });
 
+    // fromInt : Attr * Int -> Attr * Str
+    add_type(Symbol::STR_FROM_INT, {
+        let_tvars! { star1, star2 };
+        unique_function(vec![int_type(star1)], str_type(star2))
+    });
+
     // Result module
 
     // map : Attr * (Result (Attr a e))
diff --git a/compiler/can/src/builtins.rs b/compiler/can/src/builtins.rs
index 021f14e5f2..7b1d737898 100644
--- a/compiler/can/src/builtins.rs
+++ b/compiler/can/src/builtins.rs
@@ -56,6 +56,7 @@ pub fn builtin_defs(var_store: &mut VarStore) -> MutMap<Symbol, Def> {
         Symbol::STR_STARTS_WITH => str_starts_with,
         Symbol::STR_ENDS_WITH => str_ends_with,
         Symbol::STR_COUNT_GRAPHEMES => str_count_graphemes,
+        Symbol::STR_FROM_INT => str_from_int,
         Symbol::LIST_LEN => list_len,
         Symbol::LIST_GET => list_get,
         Symbol::LIST_SET => list_set,
@@ -1030,6 +1031,26 @@ fn str_count_graphemes(symbol: Symbol, var_store: &mut VarStore) -> Def {
     )
 }
 
+/// Str.fromInt : Int -> Str
+fn str_from_int(symbol: Symbol, var_store: &mut VarStore) -> Def {
+    let int_var = var_store.fresh();
+    let str_var = var_store.fresh();
+
+    let body = RunLowLevel {
+        op: LowLevel::StrFromInt,
+        args: vec![(int_var, Var(Symbol::ARG_1))],
+        ret_var: str_var,
+    };
+
+    defn(
+        symbol,
+        vec![(int_var, Symbol::ARG_1)],
+        var_store,
+        body,
+        str_var,
+    )
+}
+
 /// List.concat : List elem, List elem -> List elem
 fn list_concat(symbol: Symbol, var_store: &mut VarStore) -> Def {
     let list_var = var_store.fresh();
diff --git a/compiler/gen/src/llvm/build.rs b/compiler/gen/src/llvm/build.rs
index b428c28491..0c87627943 100644
--- a/compiler/gen/src/llvm/build.rs
+++ b/compiler/gen/src/llvm/build.rs
@@ -4,8 +4,8 @@ use crate::llvm::build_list::{
     list_reverse, list_set, list_single, list_sum, list_walk, list_walk_backwards,
 };
 use crate::llvm::build_str::{
-    str_concat, str_count_graphemes, str_ends_with, str_len, str_split, str_starts_with,
-    CHAR_LAYOUT,
+    str_concat, str_count_graphemes, str_ends_with, str_from_int, str_number_of_bytes, str_split,
+    str_starts_with, CHAR_LAYOUT,
 };
 use crate::llvm::compare::{build_eq, build_neq};
 use crate::llvm::convert::{
@@ -2427,23 +2427,25 @@ fn run_low_level<'a, 'ctx, 'env>(
 
             let inplace = get_inplace_from_layout(layout);
 
-            str_concat(env, inplace, scope, parent, args[0], args[1])
+            str_concat(env, inplace, scope, args[0], args[1])
         }
         StrStartsWith => {
             // Str.startsWith : Str, Str -> Bool
             debug_assert_eq!(args.len(), 2);
 
-            let inplace = get_inplace_from_layout(layout);
-
-            str_starts_with(env, inplace, scope, parent, args[0], args[1])
+            str_starts_with(env, scope, args[0], args[1])
         }
         StrEndsWith => {
             // Str.startsWith : Str, Str -> Bool
             debug_assert_eq!(args.len(), 2);
 
-            let inplace = get_inplace_from_layout(layout);
+            str_ends_with(env, scope, args[0], args[1])
+        }
+        StrFromInt => {
+            // Str.fromInt : Int -> Str
+            debug_assert_eq!(args.len(), 1);
 
-            str_ends_with(env, inplace, scope, parent, args[0], args[1])
+            str_from_int(env, scope, args[0])
         }
         StrSplit => {
             // Str.split : Str, Str -> List Str
@@ -2451,13 +2453,13 @@ fn run_low_level<'a, 'ctx, 'env>(
 
             let inplace = get_inplace_from_layout(layout);
 
-            str_split(env, scope, parent, inplace, args[0], args[1])
+            str_split(env, scope, inplace, args[0], args[1])
         }
         StrIsEmpty => {
             // Str.isEmpty : Str -> Str
             debug_assert_eq!(args.len(), 1);
 
-            let len = str_len(env, scope, args[0]);
+            let len = str_number_of_bytes(env, scope, args[0]);
             let is_zero = env.builder.build_int_compare(
                 IntPredicate::EQ,
                 len,
@@ -2470,7 +2472,7 @@ fn run_low_level<'a, 'ctx, 'env>(
             // Str.countGraphemes : Str -> Int
             debug_assert_eq!(args.len(), 1);
 
-            str_count_graphemes(env, scope, parent, args[0])
+            str_count_graphemes(env, scope, args[0])
         }
         ListLen => {
             // List.len : List * -> Int
diff --git a/compiler/gen/src/llvm/build_list.rs b/compiler/gen/src/llvm/build_list.rs
index 9c6c20bbb7..4049f38e05 100644
--- a/compiler/gen/src/llvm/build_list.rs
+++ b/compiler/gen/src/llvm/build_list.rs
@@ -3,7 +3,7 @@ use crate::llvm::build::{
 };
 use crate::llvm::compare::build_eq;
 use crate::llvm::convert::{basic_type_from_layout, collection, get_ptr_type};
-use crate::llvm::refcounting::decrement_refcount_layout;
+use crate::llvm::refcounting::{decrement_refcount_layout, increment_refcount_layout};
 use inkwell::builder::Builder;
 use inkwell::context::Context;
 use inkwell::types::{BasicTypeEnum, PointerType};
@@ -1318,6 +1318,85 @@ pub fn list_keep_if_help<'a, 'ctx, 'env>(
     }
 }
 
+/// List.map : List before, (before -> after) -> List after
+macro_rules! list_map_help {
+    ($env:expr, $layout_ids:expr, $inplace:expr, $parent:expr, $func:expr, $func_layout:expr, $list:expr, $list_layout:expr, $function_ptr:expr, $function_return_layout: expr, $closure_info:expr) => {{
+        let layout_ids = $layout_ids;
+        let inplace = $inplace;
+        let parent = $parent;
+        let func = $func;
+        let func_layout = $func_layout;
+        let list = $list;
+        let list_layout = $list_layout;
+        let function_ptr = $function_ptr;
+        let function_return_layout = $function_return_layout;
+        let closure_info : Option<(&Layout, BasicValueEnum)> = $closure_info;
+
+
+        let non_empty_fn = |elem_layout: &Layout<'a>,
+                            len: IntValue<'ctx>,
+                            list_wrapper: StructValue<'ctx>| {
+            let ctx = $env.context;
+            let builder = $env.builder;
+
+            let ret_list_ptr = allocate_list($env, inplace, function_return_layout, len);
+
+            let elem_type = basic_type_from_layout($env.arena, ctx, elem_layout, $env.ptr_bytes);
+            let ptr_type = get_ptr_type(&elem_type, AddressSpace::Generic);
+
+            let list_ptr = load_list_ptr(builder, list_wrapper, ptr_type);
+
+            let list_loop = |index, before_elem| {
+                increment_refcount_layout($env, parent, layout_ids, before_elem, elem_layout);
+
+                let arguments = match closure_info {
+                    Some((closure_data_layout, closure_data)) => {
+                        increment_refcount_layout( $env, parent, layout_ids, closure_data, closure_data_layout);
+
+                        bumpalo::vec![in $env.arena; before_elem, closure_data]
+                    }
+                    None => bumpalo::vec![in $env.arena; before_elem],
+                };
+
+
+                let call_site_value = builder.build_call(function_ptr, &arguments, "map_func");
+
+                // set the calling convention explicitly for this call
+                call_site_value.set_call_convention(crate::llvm::build::FAST_CALL_CONV);
+
+                let after_elem = call_site_value
+                    .try_as_basic_value()
+                    .left()
+                    .unwrap_or_else(|| panic!("LLVM error: Invalid call by pointer."));
+
+                // The pointer to the element in the mapped-over list
+                let after_elem_ptr = unsafe {
+                    builder.build_in_bounds_gep(ret_list_ptr, &[index], "load_index_after_list")
+                };
+
+                // Mutate the new array in-place to change the element.
+                builder.build_store(after_elem_ptr, after_elem);
+            };
+
+            incrementing_elem_loop(builder, ctx, parent, list_ptr, len, "#index", list_loop);
+
+            let result = store_list($env, ret_list_ptr, len);
+
+            // decrement the input list and function (if it's a closure)
+            decrement_refcount_layout($env, parent, layout_ids, list, list_layout);
+            decrement_refcount_layout($env, parent, layout_ids, func, func_layout);
+
+            if let Some((closure_data_layout, closure_data))  = closure_info  {
+                decrement_refcount_layout( $env, parent, layout_ids, closure_data, closure_data_layout);
+            }
+
+            result
+        };
+
+        if_list_is_not_empty($env, parent, non_empty_fn, list, list_layout, "List.map")
+    }};
+}
+
 /// List.map : List before, (before -> after) -> List after
 #[allow(clippy::too_many_arguments)]
 pub fn list_map<'a, 'ctx, 'env>(
@@ -1332,104 +1411,50 @@ pub fn list_map<'a, 'ctx, 'env>(
 ) -> BasicValueEnum<'ctx> {
     match (func, func_layout) {
         (BasicValueEnum::PointerValue(func_ptr), Layout::FunctionPointer(_, ret_elem_layout)) => {
-            let non_empty_fn = |elem_layout: &Layout<'a>,
-                                len: IntValue<'ctx>,
-                                list_wrapper: StructValue<'ctx>| {
-                let ctx = env.context;
-                let builder = env.builder;
-
-                let ret_list_ptr = allocate_list(env, inplace, ret_elem_layout, len);
-
-                let elem_type = basic_type_from_layout(env.arena, ctx, elem_layout, env.ptr_bytes);
-                let ptr_type = get_ptr_type(&elem_type, AddressSpace::Generic);
-
-                let list_ptr = load_list_ptr(builder, list_wrapper, ptr_type);
-
-                let list_loop = |index, before_elem| {
-                    let call_site_value =
-                        builder.build_call(func_ptr, env.arena.alloc([before_elem]), "map_func");
-
-                    // set the calling convention explicitly for this call
-                    call_site_value.set_call_convention(crate::llvm::build::FAST_CALL_CONV);
-
-                    let after_elem = call_site_value
-                        .try_as_basic_value()
-                        .left()
-                        .unwrap_or_else(|| panic!("LLVM error: Invalid call by pointer."));
-
-                    // The pointer to the element in the mapped-over list
-                    let after_elem_ptr = unsafe {
-                        builder.build_in_bounds_gep(ret_list_ptr, &[index], "load_index_after_list")
-                    };
-
-                    // Mutate the new array in-place to change the element.
-                    builder.build_store(after_elem_ptr, after_elem);
-                };
-
-                incrementing_elem_loop(builder, ctx, parent, list_ptr, len, "#index", list_loop);
-
-                let result = store_list(env, ret_list_ptr, len);
-
-                decrement_refcount_layout(env, parent, layout_ids, list, list_layout);
-
-                result
-            };
-
-            if_list_is_not_empty(env, parent, non_empty_fn, list, list_layout, "List.map")
+            list_map_help!(
+                env,
+                layout_ids,
+                inplace,
+                parent,
+                func,
+                func_layout,
+                list,
+                list_layout,
+                func_ptr,
+                ret_elem_layout,
+                None
+            )
         }
-        (BasicValueEnum::StructValue(ptr_and_data), Layout::Closure(_, _, ret_elem_layout)) => {
-            let non_empty_fn = |elem_layout: &Layout<'a>,
-                                len: IntValue<'ctx>,
-                                list_wrapper: StructValue<'ctx>| {
-                let ctx = env.context;
-                let builder = env.builder;
+        (
+            BasicValueEnum::StructValue(ptr_and_data),
+            Layout::Closure(_, closure_layout, ret_elem_layout),
+        ) => {
+            let builder = env.builder;
 
-                let func_ptr = builder
-                    .build_extract_value(ptr_and_data, 0, "function_ptr")
-                    .unwrap()
-                    .into_pointer_value();
+            let func_ptr = builder
+                .build_extract_value(ptr_and_data, 0, "function_ptr")
+                .unwrap()
+                .into_pointer_value();
 
-                let closure_data = builder
-                    .build_extract_value(ptr_and_data, 1, "closure_data")
-                    .unwrap();
+            let closure_data = builder
+                .build_extract_value(ptr_and_data, 1, "closure_data")
+                .unwrap();
 
-                let ret_list_ptr = allocate_list(env, inplace, ret_elem_layout, len);
+            let closure_data_layout = closure_layout.as_block_of_memory_layout();
 
-                let elem_type = basic_type_from_layout(env.arena, ctx, elem_layout, env.ptr_bytes);
-                let ptr_type = get_ptr_type(&elem_type, AddressSpace::Generic);
-
-                let list_ptr = load_list_ptr(builder, list_wrapper, ptr_type);
-
-                let list_loop = |index, before_elem| {
-                    let call_site_value = builder.build_call(
-                        func_ptr,
-                        env.arena.alloc([before_elem, closure_data]),
-                        "map_func",
-                    );
-
-                    // set the calling convention explicitly for this call
-                    call_site_value.set_call_convention(crate::llvm::build::FAST_CALL_CONV);
-
-                    let after_elem = call_site_value
-                        .try_as_basic_value()
-                        .left()
-                        .unwrap_or_else(|| panic!("LLVM error: Invalid call by pointer."));
-
-                    // The pointer to the element in the mapped-over list
-                    let after_elem_ptr = unsafe {
-                        builder.build_in_bounds_gep(ret_list_ptr, &[index], "load_index_after_list")
-                    };
-
-                    // Mutate the new array in-place to change the element.
-                    builder.build_store(after_elem_ptr, after_elem);
-                };
-
-                incrementing_elem_loop(builder, ctx, parent, list_ptr, len, "#index", list_loop);
-
-                store_list(env, ret_list_ptr, len)
-            };
-
-            if_list_is_not_empty(env, parent, non_empty_fn, list, list_layout, "List.map")
+            list_map_help!(
+                env,
+                layout_ids,
+                inplace,
+                parent,
+                func,
+                func_layout,
+                list,
+                list_layout,
+                func_ptr,
+                ret_elem_layout,
+                Some((&closure_data_layout, closure_data))
+            )
         }
         _ => {
             unreachable!(
diff --git a/compiler/gen/src/llvm/build_str.rs b/compiler/gen/src/llvm/build_str.rs
index 209a125b13..3a021dd10d 100644
--- a/compiler/gen/src/llvm/build_str.rs
+++ b/compiler/gen/src/llvm/build_str.rs
@@ -4,19 +4,20 @@ use crate::llvm::build::{
 use crate::llvm::build_list::{allocate_list, store_list};
 use crate::llvm::convert::collection;
 use inkwell::types::BasicTypeEnum;
-use inkwell::values::{BasicValueEnum, FunctionValue, IntValue, StructValue};
+use inkwell::values::{BasicValueEnum, IntValue, StructValue};
 use inkwell::AddressSpace;
 use roc_builtins::bitcode;
 use roc_module::symbol::Symbol;
 use roc_mono::layout::{Builtin, Layout};
 
+use super::build::load_symbol;
+
 pub static CHAR_LAYOUT: Layout = Layout::Builtin(Builtin::Int8);
 
 /// Str.split : Str, Str -> List Str
 pub fn str_split<'a, 'ctx, 'env>(
     env: &Env<'a, 'ctx, 'env>,
     scope: &Scope<'a, 'ctx>,
-    _parent: FunctionValue<'ctx>,
     inplace: InPlace,
     str_symbol: Symbol,
     delimiter_symbol: Symbol,
@@ -60,29 +61,6 @@ pub fn str_split<'a, 'ctx, 'env>(
     store_list(env, ret_list_ptr, segment_count)
 }
 
-/*
-fn cast_to_zig_str(
-    env: &Env<'a, 'ctx, 'env>,
-    str_as_struct: StructValue<'ctx>,
-) -> BasicValueEnum<'ctx> {
-    // get the RocStr type defined by zig
-    let roc_str_type = env.module.get_struct_type("str.RocStr").unwrap();
-
-    // convert `{ *mut u8, i64 }` to `RocStr`
-    builder.build_bitcast(str_as_struct, roc_str_type, "convert_to_zig_rocstr");
-}
-
-fn cast_from_zig_str(
-    env: &Env<'a, 'ctx, 'env>,
-    str_as_struct: StructValue<'ctx>,
-) -> BasicValueEnum<'ctx> {
-    let ret_type = BasicTypeEnum::StructType(collection(ctx, env.ptr_bytes));
-
-    // convert `RocStr` to `{ *mut u8, i64 }`
-    builder.build_bitcast(str_as_struct, ret_type, "convert_from_zig_rocstr");
-}
-*/
-
 fn str_symbol_to_i128<'a, 'ctx, 'env>(
     env: &Env<'a, 'ctx, 'env>,
     scope: &Scope<'a, 'ctx>,
@@ -144,7 +122,6 @@ pub fn str_concat<'a, 'ctx, 'env>(
     env: &Env<'a, 'ctx, 'env>,
     inplace: InPlace,
     scope: &Scope<'a, 'ctx>,
-    _parent: FunctionValue<'ctx>,
     str1_symbol: Symbol,
     str2_symbol: Symbol,
 ) -> BasicValueEnum<'ctx> {
@@ -173,7 +150,7 @@ pub fn str_concat<'a, 'ctx, 'env>(
     zig_str_to_struct(env, zig_result).into()
 }
 
-pub fn str_len<'a, 'ctx, 'env>(
+pub fn str_number_of_bytes<'a, 'ctx, 'env>(
     env: &Env<'a, 'ctx, 'env>,
     scope: &Scope<'a, 'ctx>,
     str_symbol: Symbol,
@@ -181,7 +158,8 @@ pub fn str_len<'a, 'ctx, 'env>(
     let str_i128 = str_symbol_to_i128(env, scope, str_symbol);
 
     // the builtin will always return an u64
-    let length = call_bitcode_fn(env, &[str_i128.into()], &bitcode::STR_LEN).into_int_value();
+    let length =
+        call_bitcode_fn(env, &[str_i128.into()], &bitcode::STR_NUMBER_OF_BYTES).into_int_value();
 
     // cast to the appropriate usize of the current build
     env.builder
@@ -191,9 +169,7 @@ pub fn str_len<'a, 'ctx, 'env>(
 /// Str.startsWith : Str, Str -> Bool
 pub fn str_starts_with<'a, 'ctx, 'env>(
     env: &Env<'a, 'ctx, 'env>,
-    _inplace: InPlace,
     scope: &Scope<'a, 'ctx>,
-    _parent: FunctionValue<'ctx>,
     str_symbol: Symbol,
     prefix_symbol: Symbol,
 ) -> BasicValueEnum<'ctx> {
@@ -210,9 +186,7 @@ pub fn str_starts_with<'a, 'ctx, 'env>(
 /// Str.endsWith : Str, Str -> Bool
 pub fn str_ends_with<'a, 'ctx, 'env>(
     env: &Env<'a, 'ctx, 'env>,
-    _inplace: InPlace,
     scope: &Scope<'a, 'ctx>,
-    _parent: FunctionValue<'ctx>,
     str_symbol: Symbol,
     prefix_symbol: Symbol,
 ) -> BasicValueEnum<'ctx> {
@@ -230,7 +204,6 @@ pub fn str_ends_with<'a, 'ctx, 'env>(
 pub fn str_count_graphemes<'a, 'ctx, 'env>(
     env: &Env<'a, 'ctx, 'env>,
     scope: &Scope<'a, 'ctx>,
-    _parent: FunctionValue<'ctx>,
     str_symbol: Symbol,
 ) -> BasicValueEnum<'ctx> {
     let str_i128 = str_symbol_to_i128(env, scope, str_symbol);
@@ -241,3 +214,16 @@ pub fn str_count_graphemes<'a, 'ctx, 'env>(
         &bitcode::STR_COUNT_GRAPEHEME_CLUSTERS,
     )
 }
+
+/// Str.fromInt : Int -> Str
+pub fn str_from_int<'a, 'ctx, 'env>(
+    env: &Env<'a, 'ctx, 'env>,
+    scope: &Scope<'a, 'ctx>,
+    int_symbol: Symbol,
+) -> BasicValueEnum<'ctx> {
+    let int = load_symbol(env, scope, &int_symbol);
+
+    let zig_result = call_bitcode_fn(env, &[int], &bitcode::STR_FROM_INT).into_struct_value();
+
+    zig_str_to_struct(env, zig_result).into()
+}
diff --git a/compiler/gen/src/llvm/refcounting.rs b/compiler/gen/src/llvm/refcounting.rs
index 60e252e075..0ef67b4960 100644
--- a/compiler/gen/src/llvm/refcounting.rs
+++ b/compiler/gen/src/llvm/refcounting.rs
@@ -2,7 +2,7 @@ use crate::llvm::build::{
     cast_basic_basic, cast_struct_struct, create_entry_block_alloca, set_name, Env, Scope,
     FAST_CALL_CONV, LLVM_SADD_WITH_OVERFLOW_I64,
 };
-use crate::llvm::build_list::list_len;
+use crate::llvm::build_list::{incrementing_elem_loop, list_len, load_list};
 use crate::llvm::convert::{basic_type_from_layout, block_of_memory, ptr_int};
 use bumpalo::collections::Vec;
 use inkwell::context::Context;
@@ -367,7 +367,6 @@ fn decrement_refcount_builtin<'a, 'ctx, 'env>(
         List(memory_mode, element_layout) => {
             let wrapper_struct = value.into_struct_value();
             if element_layout.contains_refcounted() {
-                use crate::llvm::build_list::{incrementing_elem_loop, load_list};
                 use inkwell::types::BasicType;
 
                 let ptr_type =
@@ -451,7 +450,6 @@ fn increment_refcount_builtin<'a, 'ctx, 'env>(
         List(memory_mode, element_layout) => {
             let wrapper_struct = value.into_struct_value();
             if element_layout.contains_refcounted() {
-                use crate::llvm::build_list::{incrementing_elem_loop, load_list};
                 use inkwell::types::BasicType;
 
                 let ptr_type =
diff --git a/compiler/gen/tests/gen_str.rs b/compiler/gen/tests/gen_str.rs
index d45070a879..027471be3c 100644
--- a/compiler/gen/tests/gen_str.rs
+++ b/compiler/gen/tests/gen_str.rs
@@ -490,4 +490,29 @@ mod gen_str {
     fn str_starts_with_false_small_str() {
         assert_evals_to!(r#"Str.startsWith "1234" "23""#, false, bool);
     }
+
+    #[test]
+    fn str_from_int() {
+        assert_evals_to!(
+            r#"Str.fromInt 1234"#,
+            roc_std::RocStr::from_slice("1234".as_bytes()),
+            roc_std::RocStr
+        );
+        assert_evals_to!(
+            r#"Str.fromInt 0"#,
+            roc_std::RocStr::from_slice("0".as_bytes()),
+            roc_std::RocStr
+        );
+        assert_evals_to!(
+            r#"Str.fromInt -1"#,
+            roc_std::RocStr::from_slice("-1".as_bytes()),
+            roc_std::RocStr
+        );
+
+        let max = format!("{}", i64::MAX);
+        assert_evals_to!(r#"Str.fromInt Num.maxInt"#, &max, &'static str);
+
+        let min = format!("{}", i64::MIN);
+        assert_evals_to!(r#"Str.fromInt Num.minInt"#, &min, &'static str);
+    }
 }
diff --git a/compiler/module/src/low_level.rs b/compiler/module/src/low_level.rs
index 887e836952..db9617ded4 100644
--- a/compiler/module/src/low_level.rs
+++ b/compiler/module/src/low_level.rs
@@ -9,6 +9,7 @@ pub enum LowLevel {
     StrEndsWith,
     StrSplit,
     StrCountGraphemes,
+    StrFromInt,
     ListLen,
     ListGetUnsafe,
     ListSet,
diff --git a/compiler/module/src/symbol.rs b/compiler/module/src/symbol.rs
index 8d05487f96..c434a01c4c 100644
--- a/compiler/module/src/symbol.rs
+++ b/compiler/module/src/symbol.rs
@@ -749,6 +749,7 @@ define_builtins! {
         6 STR_COUNT_GRAPHEMES: "countGraphemes"
         7 STR_STARTS_WITH: "startsWith"
         8 STR_ENDS_WITH: "endsWith"
+        9 STR_FROM_INT: "fromInt"
     }
     4 LIST: "List" => {
         0 LIST_LIST: "List" imported // the List.List type alias
diff --git a/compiler/mono/src/borrow.rs b/compiler/mono/src/borrow.rs
index b9cef5a4ba..b100625fbc 100644
--- a/compiler/mono/src/borrow.rs
+++ b/compiler/mono/src/borrow.rs
@@ -548,5 +548,6 @@ pub fn lowlevel_borrow_signature(arena: &Bump, op: LowLevel) -> &[bool] {
             arena.alloc_slice_copy(&[irrelevant])
         }
         StrStartsWith | StrEndsWith => arena.alloc_slice_copy(&[owned, borrowed]),
+        StrFromInt => arena.alloc_slice_copy(&[irrelevant]),
     }
 }
diff --git a/compiler/mono/src/layout.rs b/compiler/mono/src/layout.rs
index c54e39564f..91b2e3986e 100644
--- a/compiler/mono/src/layout.rs
+++ b/compiler/mono/src/layout.rs
@@ -460,7 +460,7 @@ impl<'a> Layout<'a> {
 
     pub fn is_refcounted(&self) -> bool {
         match self {
-            Layout::Builtin(Builtin::List(_, _)) => true,
+            Layout::Builtin(Builtin::List(MemoryMode::Refcounted, _)) => true,
             Layout::Builtin(Builtin::Str) => true,
             Layout::RecursiveUnion(_) => true,
             Layout::RecursivePointer => true,
@@ -477,12 +477,12 @@ impl<'a> Layout<'a> {
         match self {
             Builtin(builtin) => builtin.is_refcounted(),
             PhantomEmptyStruct => false,
-            Struct(fields) => fields.iter().any(|f| f.is_refcounted()),
+            Struct(fields) => fields.iter().any(|f| f.contains_refcounted()),
             Union(fields) => fields
                 .iter()
                 .map(|ls| ls.iter())
                 .flatten()
-                .any(|f| f.is_refcounted()),
+                .any(|f| f.contains_refcounted()),
             RecursiveUnion(_) => true,
             Closure(_, closure_layout, _) => closure_layout.contains_refcounted(),
             FunctionPointer(_, _) | RecursivePointer | Pointer(_) => false,
diff --git a/compiler/mono/tests/test_mono.rs b/compiler/mono/tests/test_mono.rs
index c7d7ba58d6..2f2f834362 100644
--- a/compiler/mono/tests/test_mono.rs
+++ b/compiler/mono/tests/test_mono.rs
@@ -1851,7 +1851,6 @@ mod test_mono {
                     let Test.2 = S Test.9 Test.8;
                     let Test.5 = 1i64;
                     let Test.6 = Index 0 Test.2;
-                    dec Test.2;
                     let Test.7 = lowlevel Eq Test.5 Test.6;
                     if Test.7 then
                         let Test.3 = 0i64;
@@ -1903,15 +1902,12 @@ mod test_mono {
                         let Test.10 = lowlevel Eq Test.8 Test.9;
                         if Test.10 then
                             let Test.4 = Index 1 Test.2;
-                            dec Test.2;
                             let Test.3 = 1i64;
                             ret Test.3;
                         else
-                            dec Test.2;
                             let Test.5 = 0i64;
                             ret Test.5;
                     else
-                        dec Test.2;
                         let Test.6 = 0i64;
                         ret Test.6;
                 "#
diff --git a/editor/Cargo.toml b/editor/Cargo.toml
index 4587d2ce80..7dec086b0e 100644
--- a/editor/Cargo.toml
+++ b/editor/Cargo.toml
@@ -23,6 +23,8 @@ roc_solve = { path = "../compiler/solve" }
 roc_mono = { path = "../compiler/mono" }
 roc_load = { path = "../compiler/load" }
 roc_gen = { path = "../compiler/gen" }
+roc_fmt = { path = "../compiler/fmt" }
+
 roc_reporting = { path = "../compiler/reporting" }
  # TODO switch to clap 3.0.0 once it's out. Tried adding clap = "~3.0.0-beta.1" and cargo wouldn't accept it
 im    = "14" # im and im-rc should always have the same version!
diff --git a/editor/src/file.rs b/editor/src/file.rs
new file mode 100644
index 0000000000..da8328fdaf
--- /dev/null
+++ b/editor/src/file.rs
@@ -0,0 +1,97 @@
+use bumpalo::collections::Vec;
+use bumpalo::Bump;
+use roc_fmt::def::fmt_def;
+use roc_fmt::module::fmt_module;
+use roc_parse::ast::{Attempting, Def, Module};
+use roc_parse::module::module_defs;
+use roc_parse::parser;
+use roc_parse::parser::Parser;
+use roc_region::all::Located;
+use std::ffi::OsStr;
+use std::path::Path;
+use std::{fs, io};
+
+#[derive(Debug)]
+pub struct File<'a> {
+    path: &'a Path,
+    module_header: Module<'a>,
+    content: Vec<'a, Located<Def<'a>>>,
+}
+
+#[derive(Debug)]
+pub enum ReadError {
+    Read(std::io::Error),
+    ParseDefs(parser::Fail),
+    ParseHeader(parser::Fail),
+    DoesntHaveRocExtension,
+}
+
+impl<'a> File<'a> {
+    pub fn read(path: &'a Path, arena: &'a Bump) -> Result<File<'a>, ReadError> {
+        if path.extension() != Some(OsStr::new("roc")) {
+            return Err(ReadError::DoesntHaveRocExtension);
+        }
+
+        let bytes = fs::read(path).map_err(ReadError::Read)?;
+
+        let allocation = arena.alloc(bytes);
+
+        let module_parse_state = parser::State::new(allocation, Attempting::Module);
+        let parsed_module = roc_parse::module::header().parse(&arena, module_parse_state);
+
+        match parsed_module {
+            Ok((module, state)) => {
+                let parsed_defs = module_defs().parse(&arena, state);
+
+                match parsed_defs {
+                    Ok((defs, _)) => Ok(File {
+                        path,
+                        module_header: module,
+                        content: defs,
+                    }),
+                    Err((error, _)) => Err(ReadError::ParseDefs(error)),
+                }
+            }
+            Err((error, _)) => Err(ReadError::ParseHeader(error)),
+        }
+    }
+
+    pub fn fmt(&self) -> String {
+        let arena = Bump::new();
+        let mut formatted_file = String::new();
+
+        let mut module_header_buf = bumpalo::collections::String::new_in(&arena);
+        fmt_module(&mut module_header_buf, &self.module_header);
+
+        formatted_file.push_str(module_header_buf.as_str());
+
+        for def in &self.content {
+            let mut def_buf = bumpalo::collections::String::new_in(&arena);
+
+            fmt_def(&mut def_buf, &def.value, 0);
+
+            formatted_file.push_str(def_buf.as_str());
+        }
+
+        formatted_file
+    }
+
+    pub fn fmt_then_write_to(&self, write_path: &'a Path) -> io::Result<()> {
+        let formatted_file = self.fmt();
+
+        fs::write(write_path, formatted_file)
+    }
+
+    pub fn fmt_then_write_with_name(&self, new_name: &str) -> io::Result<()> {
+        self.fmt_then_write_to(
+            self.path
+                .with_file_name(new_name)
+                .with_extension("roc")
+                .as_path(),
+        )
+    }
+
+    pub fn fmt_then_write(&self) -> io::Result<()> {
+        self.fmt_then_write_to(self.path)
+    }
+}
diff --git a/editor/src/lib.rs b/editor/src/lib.rs
index d0b5ef881b..7a5c178d00 100644
--- a/editor/src/lib.rs
+++ b/editor/src/lib.rs
@@ -22,6 +22,7 @@ use winit::event::{ElementState, ModifiersState, VirtualKeyCode};
 use winit::event_loop::ControlFlow;
 
 pub mod ast;
+pub mod file;
 mod rect;
 pub mod text_state;
 mod vertex;
diff --git a/editor/tests/modules/Simple.roc b/editor/tests/modules/Simple.roc
new file mode 100644
index 0000000000..0b083ca390
--- /dev/null
+++ b/editor/tests/modules/Simple.roc
@@ -0,0 +1,26 @@
+interface Simple
+    exposes [
+    v, x
+     ]
+    imports       []
+
+
+
+
+
+
+
+
+
+v :      Str
+
+
+
+
+
+v = "Value!"
+
+
+
+x : Int
+x = 4
\ No newline at end of file
diff --git a/editor/tests/modules/Storage.roc b/editor/tests/modules/Storage.roc
new file mode 100644
index 0000000000..950d1d01f1
--- /dev/null
+++ b/editor/tests/modules/Storage.roc
@@ -0,0 +1,68 @@
+interface Storage
+    exposes [
+        Storage,
+        decoder,
+        get,
+        listener,
+        set
+    ]
+    imports [
+        Map.{ Map },
+        Json.Decode.{ Decoder } as Decode
+        Json.Encode as Encode
+        Ports.FromJs as FromJs
+        Ports.ToJs as ToJs
+    ]
+
+
+################################################################################
+## TYPES ##
+################################################################################
+
+
+Storage : [
+    @Storage (Map Str Decode.Value)
+]
+
+
+################################################################################
+## API ##
+################################################################################
+
+
+get : Storage, Str, Decoder a -> [ Ok a, NotInStorage, DecodeError Decode.Error ]*
+get = \key, decoder, @Storage map ->
+    when Map.get map key is
+        Ok json ->
+            Decode.decodeValue decoder json
+
+        Err NotFound ->
+            NotInStorage
+
+
+set : Encode.Value, Str -> Effect {}
+set json str =
+    ToJs.type "setStorage"
+        |> ToJs.setFields [
+            Field "key" (Encode.str str),
+            Field "value" json
+        ]
+        |> ToJs.send
+
+
+decoder : Decoder Storage
+decoder =
+    Decode.mapType Decode.value
+        |> Decode.map \map -> @Storage map
+
+
+################################################################################
+## PORTS INCOMING ##
+################################################################################
+
+
+listener : (Storage -> msg) -> FromJs.Listener msg
+listener toMsg =
+    FromJs.listen "storageUpdated"
+        (Decode.map decoder toMsg)
+
diff --git a/editor/tests/test_file.rs b/editor/tests/test_file.rs
new file mode 100644
index 0000000000..e5a8059c2c
--- /dev/null
+++ b/editor/tests/test_file.rs
@@ -0,0 +1,40 @@
+#[macro_use]
+extern crate pretty_assertions;
+#[macro_use]
+extern crate indoc;
+
+#[cfg(test)]
+mod test_file {
+    use bumpalo::Bump;
+    use roc_editor::file::File;
+    use std::path::Path;
+
+    #[test]
+    fn read_and_fmt_simple_roc_module() {
+        let simple_module_path = Path::new("./tests/modules/Simple.roc");
+
+        let arena = Bump::new();
+
+        let file = File::read(simple_module_path, &arena)
+            .expect("Could not read Simple.roc in test_file test");
+
+        assert_eq!(
+            file.fmt(),
+            indoc!(
+                r#"
+                    interface Simple
+                        exposes [ 
+                        v, x
+                         ]
+                        imports []
+    
+                    v : Str
+                    
+                    v = "Value!"
+
+                    x : Int
+                    x = 4"#
+            )
+        );
+    }
+}
diff --git a/examples/effect/Main.roc b/examples/effect/Main.roc
index 59aaeedf94..9295df2d36 100644
--- a/examples/effect/Main.roc
+++ b/examples/effect/Main.roc
@@ -5,4 +5,16 @@ app "effect-example"
 
 main : Task {}
 main =
-    Task.putLine "Hello world"
+    when if 1 == 1 then True 3 else False 3.14 is
+        True n -> Effect.putLine (Str.fromInt n)
+        _ -> Effect.putLine "Yay"
+
+# main : Effect.Effect {} as Fx
+# main =
+#     if RBTree.isEmpty (RBTree.insert 1 2 Empty) then
+#         Effect.putLine "Yay"
+#             |> Effect.after (\{} -> Effect.getLine)
+#             |> Effect.after (\line -> Effect.putLine line)
+#     else
+#         Effect.putLine "Nay"
+#