Move purescript-symbols in

Author: LiamGoodacre

src/Data/Symbol.js

@@ -0,0 +1,8 @@
+"use strict";
+
+// module Data.Symbol
+
+exports.unsafeCoerce = function (arg) {
+  return arg;
+};
+

src/Data/Symbol.purs

@@ -0,0 +1,24 @@
+module Data.Symbol
+  ( class IsSymbol
+  , reflectSymbol
+  , reifySymbol
+  , SProxy(..)
+  ) where
+
+-- | A value-level proxy for a type-level symbol.
+data SProxy (sym :: Symbol) = SProxy
+
+-- | A class for known symbols
+class IsSymbol (sym :: Symbol) where
+  reflectSymbol :: SProxy sym -> String
+
+-- local definition for use in `reifySymbol`
+foreign import unsafeCoerce :: forall a b. a -> b
+
+reifySymbol :: forall r. String -> (forall sym. IsSymbol sym => SProxy sym -> r) -> r
+reifySymbol s f = coerce f { reflectSymbol: \_ -> s } SProxy where
+  coerce
+    :: (forall sym1. IsSymbol sym1              => SProxy sym1 -> r)
+    -> { reflectSymbol :: SProxy "" -> String } -> SProxy ""   -> r
+  coerce = unsafeCoerce
+