Add replaceChar helper function.

src/Base.hs

@@ -10,6 +10,7 @@ module Base (
     Args, arg,
     joinArgs, joinArgsWithSpaces,
     filterOut,
+    replaceChar
     ) where
 
 import Development.Shake hiding ((*>))
@@ -42,3 +43,8 @@ joinArgs = intercalateArgs ""
 
 filterOut :: Args -> [String] -> Args
 filterOut args list = filter (`notElem` list) <$> args
+
+replaceChar :: Char -> Char -> String -> String
+replaceChar from to = (go from) . if from == '/' then go '\\' else id
+  where
+    go from' = map (\c -> if c == from' then to else c)