Foreign.C.Enum

Documentation

enum :: String -> Name -> [Name] -> [(String, Integer)] -> DecsQ

Write like the following.

enum Foo ''Int [''Show, ''Read, ''Eq] [
	(FooError, - 1),
	(FooZero, 0),
	(FooOne, 1),
	(FooTwo, 2) ]

Then you get like the following.

newtype Foo = Foo Int deriving Eq

pattern FooError :: Int -> Foo
pattern FooError <- Foo (- 1) where
	FooError = Foo (- 1)

pattern FooZero :: Int -> Foo
...


instance Show Foo where
	showsPrec = ...

instance Read Foo where
	readPrec = ...

And you can read and show like the following.

> Foo $ - 1
FooError
> FooTwo
FooTwo
> Foo 3
Foo 3
> read "Foo (- 1)" :: Foo
FooError
> read "FooOne" :: Foo
FooOne