feat(stdlib): Add sign function to Number module (#1079)

Co-authored-by: Oscar Spencer <oscar@grain-lang.org>

compiler/test/stdlib/number.test.gr

@@ -1,5 +1,6 @@
 import Number from "number"
 import Result from "result"
+import Float64 from "float64"
 
 // add
 assert Number.add(25, 5) == 30
@@ -134,3 +135,11 @@ assert Result.isErr(Number.parseInt("zzzzz", 37))
 assert Result.isErr(Number.parseInt("zzzzz", 9223372036854775807))
 assert Result.isErr(Number.parseInt("10", 1.23))
 assert Result.isErr(Number.parseInt("10", 2/3))
+
+// Number.sign
+assert Number.sign(-10000) == -1
+assert Number.sign(22222) == 1
+// TODO(#693): Replace with Infinity literal when it exists
+assert 1 / Number.sign(0.0) == Float64.toNumber(Float64.infinity)
+// TODO(#693): Replace with -Infinity literal when it exists
+assert 1 / Number.sign(-0.0) == Number.neg(Float64.toNumber(Float64.infinity))

stdlib/number.gr

@@ -86,6 +86,24 @@ export let rec sqrt = (x: Number) => {
   ret
 }
 
+/**
+ * Determine the positivity or negativity of a Number.
+ *
+ * @param x: The number to inspect
+ * @returns `-1` if the number is negative, `1` if positive, or `0` otherwise; signedness of `-0.0` is preserved
+ *
+ * @example Number.sign(-10000) == -1
+ * @example Number.sign(222222) == 1
+ * @example Number.sign(0) == 0
+ */
+export let sign = x => {
+  match (x) {
+    x when x < 0 => -1,
+    x when x > 0 => 1,
+    _ => 0 * x,
+  }
+}
+
 /**
  * Returns the smaller of its operands.
  *

stdlib/number.md

@@ -142,6 +142,40 @@ Returns:
 |----|-----------|
 |`Number`|The square root of the operand|
 
+### Number.**sign**
+
+```grain
+sign : Number -> Number
+```
+
+Determine the positivity or negativity of a Number.
+
+Parameters:
+
+|param|type|description|
+|-----|----|-----------|
+|`x`|`Number`|The number to inspect|
+
+Returns:
+
+|type|description|
+|----|-----------|
+|`Number`|`-1` if the number is negative, `1` if positive, or `0` otherwise; signedness of `-0.0` is preserved|
+
+Examples:
+
+```grain
+Number.sign(-10000) == -1
+```
+
+```grain
+Number.sign(222222) == 1
+```
+
+```grain
+Number.sign(0) == 0
+```
+
 ### Number.**min**
 
 <details disabled>