feat(stdlib): Implement Char toString (#481)

grain-lang · Dec 17, 2020 · 37ba683 · 37ba683
1 parent 1a4c3b9
commit 37ba683
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Showing 3 changed files with 28 additions and 1 deletion.
diff --git a/compiler/test/stdlib/char.test.gr b/compiler/test/stdlib/char.test.gr
@@ -33,3 +33,7 @@ assert Char.code(Char.succ(Char.fromCode(0xD7FF))) == 0xE000
 // pred
 assert Char.code(Char.pred(Char.fromCode(0x70))) == 0x6F
 assert Char.code(Char.pred(Char.fromCode(0xE000))) == 0xD7FF
+
+// toString
+assert Char.toString('f') == "f"
+assert Char.toString('💯') == "💯"
diff --git a/stdlib/char.gr b/stdlib/char.gr
@@ -52,3 +52,8 @@ let pred = (c) => {
     fromCode(codePoint - 1)
   }
 }
+
+// Creates a new string containing the character.
+// @param char: Char - the character to convert
+// @returns String
+import foreign wasm toString : Char -> String from "stdlib-external/char"
diff --git a/stdlib/stdlib-external/char.ts b/stdlib/stdlib-external/char.ts
@@ -1,7 +1,7 @@
 import { throwError } from './ascutils/grainRuntime'
 import { GRAIN_ERR_MALFORMED_UTF8 } from './ascutils/errors'
 import { GRAIN_GENERIC_HEAP_TAG_TYPE } from './ascutils/tags'
-import { allocateChar } from './ascutils/dataStructures'
+import { allocateChar, allocateString } from './ascutils/dataStructures'
 
 // Algorithm from https://encoding.spec.whatwg.org/#utf-8-decoder
 export function code(c: u32): u32 {
@@ -85,3 +85,21 @@ export function fromCode(code: u32): u32 {
 
   return char ^ GRAIN_GENERIC_HEAP_TAG_TYPE
 }
+
+export function toString(c: u32): u32 {
+  c = c ^ GRAIN_GENERIC_HEAP_TAG_TYPE
+  let byte = load<u8>(c, 4)
+  let n: u32
+  if ((byte & 0x80) === 0x00) {
+    n = 1
+  } else if ((byte & 0xF0) === 0xF0) {
+    n = 4
+  } else if ((byte & 0xE0) === 0xE0) {
+    n = 3
+  } else {
+    n = 2
+  }
+  let str = allocateString(n)
+  memory.copy(str + 8, c + 4, n)
+  return str ^ GRAIN_GENERIC_HEAP_TAG_TYPE
+}