Move the function 'first' from Parser to MyPrelude

It is useful and generic.

MyPrelude.hs

@@ -40,3 +40,8 @@ tailInit :: [a] -> [a]
 tailInit xs
   | length xs > 2 = tail . init $ xs
   | otherwise     = []
+
+
+-- |Apply a function to the first element of a tuple.
+first :: (a -> b) -> (a,c) -> (b,c)
+first f (x,y) = (f x, y)

Parser/Core.hs

@@ -14,6 +14,7 @@ module Parser.Core (Parser,
 
 import Control.Applicative
 import Data.Char
+import MyPrelude
 
 
 -- |The parser type. It allows us to create specific parsers,
@@ -49,10 +50,6 @@ inParser :: ((String -> Maybe (a1, String))
 inParser f p = MkParser . f . runParser $ p
 
 
-first :: (a -> b) -> (a,c) -> (b,c)
-first f (x,y) = (f x, y)
-
-
 -- |Creates a Parser that parses a Char depending on a given condition.
 satisfy :: (Char -> Bool) -- ^ condition
         -> Parser Char    -- ^ created Parser