feat(stdlib): add isEmpty to String module (#1861)

Co-authored-by: Blaine Bublitz <blaine.bublitz@gmail.com>

compiler/test/stdlib/string.test.gr

@@ -63,6 +63,12 @@ assert String.byteLength("a") == 1
 assert String.byteLength(emoji) == 4
 assert String.byteLength(emojis) == 98
 
+// String.isEmpty
+assert String.isEmpty(empty) == true
+assert String.isEmpty(short) == false
+assert String.isEmpty(emoji) == false
+assert String.isEmpty(emojis) == false
+
 // indexOf tests
 assert String.indexOf(empty, empty) == Some(0)
 assert String.indexOf(empty, short) == Some(0)

stdlib/string.gr

@@ -98,6 +98,21 @@ provide let byteLength = (string: String) => {
   Conv.wasmI32ToNumber(WasmI32.load(string, 4n))
 }
 
+/**
+ * Determines if the string contains no characters.
+ *
+ * @param string: The string to inspect
+ * @returns `true` if the string is empty and `false` otherwise
+ *
+ * @since v0.6.0
+ */
+@unsafe
+provide let isEmpty = (string: String) => {
+  from WasmI32 use { (==) }
+  let strPtr = WasmI32.fromGrain(string)
+  WasmI32.load(strPtr, 4n) == 0n
+}
+
 /**
  * Finds the first position of a substring in the input string.
  *

stdlib/string.md

@@ -137,6 +137,31 @@ Examples:
 String.byteLength("🌾") == 4
 ```
 
+### String.**isEmpty**
+
+<details disabled>
+<summary tabindex="-1">Added in <code>next</code></summary>
+No other changes yet.
+</details>
+
+```grain
+isEmpty : (string: String) => Bool
+```
+
+Determines if the string contains no characters.
+
+Parameters:
+
+|param|type|description|
+|-----|----|-----------|
+|`string`|`String`|The string to inspect|
+
+Returns:
+
+|type|description|
+|----|-----------|
+|`Bool`|`true` if the string is empty and `false` otherwise|
+
 ### String.**indexOf**
 
 <details disabled>