Str.walkScalars

crates/compiler/builtins/bitcode/src/main.zig

@@ -159,6 +159,7 @@ comptime {
     exportStrFn(str.substringUnsafe, "substring_unsafe");
     exportStrFn(str.getUnsafe, "get_unsafe");
     exportStrFn(str.reserve, "reserve");
+    exportStrFn(str.getScalarUnsafe, "get_scalar_unsafe");
     exportStrFn(str.appendScalar, "append_scalar");
     exportStrFn(str.strToUtf8C, "to_utf8");
     exportStrFn(str.fromUtf8C, "from_utf8");

crates/compiler/builtins/bitcode/src/str.zig

@@ -2469,3 +2469,23 @@ pub fn reserve(string: RocStr, capacity: usize) callconv(.C) RocStr {
         return string;
     }
 }
+
+pub fn getScalarUnsafe(string: RocStr, index: usize) callconv(.C) extern struct { bytesParsed: usize, scalar: u32 } {
+    const slice = string.asSlice();
+    const bytesParsed = @intCast(usize, std.unicode.utf8ByteSequenceLength(slice[index]) catch unreachable);
+    const scalar = std.unicode.utf8Decode(slice[index .. index + bytesParsed]) catch unreachable;
+
+    return .{ .bytesParsed = bytesParsed, .scalar = @intCast(u32, scalar) };
+}
+
+test "getScalarUnsafe" {
+    const data_bytes = "A";
+    var data = RocStr.init(data_bytes, data_bytes.len);
+
+    const result = getScalarUnsafe(data, 0);
+
+    const expected = try std.unicode.utf8Decode("A");
+
+    try expectEqual(result.scalar, @intCast(u32, expected));
+    try expectEqual(result.bytesParsed, 1);
+}

crates/compiler/builtins/roc/Str.roc

@@ -39,6 +39,8 @@ interface Str
             walkUtf8WithIndex,
             reserve,
             appendScalar,
+            walkScalars,
+            walkScalarsUntil,
         ]
     imports [Bool.{ Bool }, Result.{ Result }]
 
@@ -360,3 +362,36 @@ appendScalar = \string, scalar ->
 isValidScalar : U32 -> Bool
 isValidScalar = \scalar ->
     scalar <= 0xD7FF || (scalar >= 0xE000 && scalar <= 0x10FFFF)
+
+getScalarUnsafe : Str, Nat -> { scalar : U32, bytesParsed : Nat }
+
+walkScalars : Str, state, (state, U32 -> state) -> state
+walkScalars = \string, init, step ->
+    walkScalarsHelp string init step 0 (Str.countUtf8Bytes string)
+
+walkScalarsHelp : Str, state, (state, U32 -> state), Nat, Nat -> state
+walkScalarsHelp = \string, state, step, index, length ->
+    if index < length then
+        { scalar, bytesParsed } = getScalarUnsafe string index
+        newState = step state scalar
+
+        walkScalarsHelp string newState step (index + bytesParsed) length
+    else
+        state
+
+walkScalarsUntil : Str, state, (state, U32 -> [Break state, Continue state]) -> state
+walkScalarsUntil = \string, init, step ->
+    walkScalarsUntilHelp string init step 0 (Str.countUtf8Bytes string)
+
+walkScalarsUntilHelp : Str, state, (state, U32 -> [Break state, Continue state]), Nat, Nat -> state
+walkScalarsUntilHelp = \string, state, step, index, length ->
+    if index < length then
+        { scalar, bytesParsed } = getScalarUnsafe string index
+
+        when step state scalar is
+            Continue newState ->
+                walkScalarsHelp string newState step (index + bytesParsed) length
+            Done newState ->
+                newState
+    else
+        state

crates/compiler/builtins/src/bitcode.rs

@@ -336,6 +336,7 @@ pub const STR_TRIM_RIGHT: &str = "roc_builtins.str.trim_right";
 pub const STR_GET_UNSAFE: &str = "roc_builtins.str.get_unsafe";
 pub const STR_RESERVE: &str = "roc_builtins.str.reserve";
 pub const STR_APPEND_SCALAR: &str = "roc_builtins.str.append_scalar";
+pub const STR_GET_SCALAR_UNSAFE: &str = "roc_builtins.str.get_scalar_unsafe";
 
 pub const DICT_HASH: &str = "roc_builtins.dict.hash";
 pub const DICT_HASH_STR: &str = "roc_builtins.dict.hash_str";