add type sigs

Author: davidchase

prelude.js

@@ -1,10 +1,20 @@
 'use strict';
 
+// decode :: String -> String
 const decode = decodeURIComponent;
+
+// _compose :: (b -> c) -> (a -> b) -> (a -> c)
 const _compose = (f, g) => (...args) => f(g(...args));
+
 const compose = fns => fns.reduce(_compose);
+
+// replace :: Regex -> String -> String -> String
 const replace = (pattern, substr) => str => str.replace(pattern, substr);
+
+// toLower :: String -> String
 const toLower = str => str.toLowerCase();
+
+// append :: String -> String -> String
 const append = a => b => b.concat(a);
 
 export {decode, compose, replace, toLower, append};