feat(stdlib): String.implode (#489)

grain-lang · Dec 19, 2020 · 045077b · 045077b
1 parent 1e4a691
commit 045077b
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diff --git a/compiler/test/stdlib/string.test.gr b/compiler/test/stdlib/string.test.gr
@@ -74,6 +74,11 @@ let codes = [> 119, 101, 32, 102, 111, 117, 110, 100, 32, 97, 32, 112, 97, 116,
 let chars = Array.map(Char.fromCode, codes)
 assert String.explode(emojis) == chars
 
+// implode tests
+assert String.implode([>]) == ""
+assert String.implode([> '5', ' ', '4', '3', 'a', 'b', 'c']) == "5 43abc"
+assert String.implode(String.explode(emojis)) == emojis
+
 // split tests
 assert String.split(empty, empty) == [>]
 assert String.split(short, empty) == [> "f", "o", "x"]

diff --git a/stdlib/stdlib-external/string.ts b/stdlib/stdlib-external/string.ts
@@ -106,6 +106,56 @@ export function explode(str: u32): u32 {
   return explodeHelp(str, true)
 }
 
+export function implode(arr: u32): u32 {
+  arr = arr ^ GRAIN_GENERIC_HEAP_TAG_TYPE
+
+  let arrLength = load<u32>(arr, 4)
+
+  let stringByteLength = 0
+
+  for (let i: u32 = 0; i < arrLength; i++) {
+    const char = load<u32>(arr + (i << 2), 8) ^ GRAIN_GENERIC_HEAP_TAG_TYPE
+    const byte = load<u8>(char, 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
+    }
+
+    stringByteLength += n
+  }
+
+  let str = allocateString(stringByteLength)
+  let offset = 8
+
+  for (let i: u32 = 0; i < arrLength; i++) {
+    const char = load<u32>(arr + (i << 2), 8) ^ GRAIN_GENERIC_HEAP_TAG_TYPE
+    const byte = load<u8>(char, 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
+    }
+
+    memory.copy(str + offset, char + 4, n)
+    offset += n
+  }
+
+  return str ^ GRAIN_GENERIC_HEAP_TAG_TYPE
+}
+
 export function split(str: u32, pat: u32): u32 {
   let s = str ^ GRAIN_GENERIC_HEAP_TAG_TYPE
   let p = pat ^ GRAIN_GENERIC_HEAP_TAG_TYPE

diff --git a/stdlib/string.gr b/stdlib/string.gr
@@ -35,6 +35,11 @@ let indexOf = (s, p) => {
 // @returns Array<Char>
 import foreign wasm explode : String -> Array<Char> from "stdlib-external/string"
 
+// Create a string from an array of characters
+// @param input: Array<Char> - The array to implode
+// @returns String
+import foreign wasm implode : Array<Char> -> String from "stdlib-external/string"
+
 // Split a string by the given sequence
 // @param input: String - The string to split
 // @param sequence: String - The sequence to split on