Fix signum implementation

CHANGELOG.md

@@ -5,6 +5,7 @@ Notable changes to this project are documented in this file. The format is based
 ## [Unreleased]
 
 Breaking changes:
+- Fix `signum zero` to return `zero` (#280 by @JordanMartinez)
 
 New features:
 

src/Data/Ord.purs

@@ -214,10 +214,12 @@ between low hi x
 abs :: forall a. Ord a => Ring a => a -> a
 abs x = if x >= zero then x else negate x
 
--- | The sign function; always evaluates to either `one` or `negate one`. For
--- | any `x`, we should have `signum x * abs x == x`.
+-- | The sign function; returns `one` if the argument is positive, `negate one` if the argument is negative, or `zero` if the argument is `zero`. For any `x`, we should have `signum x * abs x == x`.
 signum :: forall a. Ord a => Ring a => a -> a
-signum x = if x >= zero then one else negate one
+signum x =
+  if x < zero then negate one
+  else if x > zero then one
+  else x
 
 -- | The `Ord1` type class represents totally ordered type constructors.
 class Eq1 f <= Ord1 f where