Add fromFoldableWithIndex

Fixes #29

Author: pete-murphy

src/Foreign/Object.purs

@@ -15,6 +15,7 @@ module Foreign.Object
   , toAscUnfoldable
   , fromFoldable
   , fromFoldableWith
+  , fromFoldableWithIndex
   , fromHomogeneous
   , delete
   , pop
@@ -49,7 +50,7 @@ import Control.Monad.ST as ST
 import Data.Array as A
 import Data.Eq (class Eq1)
 import Data.Foldable (class Foldable, foldl, foldr, for_)
-import Data.FoldableWithIndex (class FoldableWithIndex)
+import Data.FoldableWithIndex (class FoldableWithIndex, forWithIndex_)
 import Data.Function.Uncurried (Fn2, runFn2, Fn4, runFn4)
 import Data.FunctorWithIndex (class FunctorWithIndex)
 import Data.Maybe (Maybe(..), maybe, fromMaybe)
@@ -221,6 +222,14 @@ fromFoldable l = runST do
   ST.foreach (A.fromFoldable l) \(Tuple k v) -> void $ OST.poke k v s
   pure s
 
+-- | Create an `Object a` from an indexed foldable collection, using the
+-- | specified function for converting the index to `String`
+fromFoldableWithIndex :: forall f k v. FoldableWithIndex k f => (k -> String) -> f v -> Object v
+fromFoldableWithIndex f l = runST do
+  s <- OST.new
+  forWithIndex_ l \k v -> OST.poke (f k) v s
+  pure s
+
 foreign import _lookupST :: forall a r z. Fn4 z (a -> z) String (STObject r a) (ST r z)
 
 -- | Create an `Object a` from a foldable collection of key/value pairs, using the