Added toUnFoldable function for Data.Maybe (#8)

* Added toUnFoldable function for Data.Maybe

This needs to go to the unfoldable package instead of the maybe package
to avoid a circular dependency.

* Added test for Maybe.toUnfoldable

* Maybe.toUnfoldable -> fromMaybe

as suggested by paf31.

Author: eskimor

src/Data/Unfoldable.purs

@@ -10,6 +10,7 @@ module Data.Unfoldable
   , replicateA
   , none
   , singleton
+  , fromMaybe
   ) where
 
 import Prelude
@@ -84,3 +85,7 @@ none = unfoldr (const Nothing) unit
 -- | ~~~
 singleton :: forall f a. Unfoldable f => a -> f a
 singleton = replicate 1
+
+-- | Convert a Maybe to any Unfoldable like lists and arrays.
+fromMaybe :: forall f a. Unfoldable f => Maybe a -> f a
+fromMaybe = unfoldr (\b -> flip Tuple Nothing <$> b)

test/Main.purs

@@ -42,4 +42,8 @@ main = do
     [2,1,1],[2,1,2], [2,2,1],[2,2,2]
   ]
 
+  log "Test Maybe.toUnfoldable"
+  assert $ U.fromMaybe (Just "a") == ["a"]
+  assert $ U.fromMaybe (Nothing :: Maybe String) == []
+
   log "All done!"