43 lines
772 B
Text
43 lines
772 B
Text
data Bool () where {
|
|
True : Bool ()
|
|
False : Bool ()
|
|
};
|
|
|
|
data List ('a) where {
|
|
Nil : List ('a)
|
|
Cons : ('a) -> List ('a) -> List ('a)
|
|
};
|
|
|
|
data Maybe ('a) where {
|
|
Nothing : Maybe ('a)
|
|
Just : 'a -> Maybe ('a)
|
|
};
|
|
|
|
data Either ('a 'b) where {
|
|
Left : 'a -> Either ('a 'b)
|
|
Right : 'b -> Either ('a 'b)
|
|
};
|
|
|
|
safeHead : List ('a) -> Maybe ('a) ;
|
|
safeHead xs =
|
|
case xs of {
|
|
Nil => Nothing ;
|
|
Cons x xs => Just x
|
|
};
|
|
|
|
main : Maybe (_Int) ;
|
|
main = safeHead (Cons 0 (Cons 1 Nil)) ;
|
|
|
|
maybeToEither : Either ('a 'b) -> Maybe ('a) ;
|
|
maybeToEither e =
|
|
case e of {
|
|
Left y => Nothing ;
|
|
Right x => Just x
|
|
};
|
|
|
|
id : 'a -> 'a ;
|
|
id x = x ;
|
|
|
|
-- Bug, occurs check failed
|
|
holdFn : Maybe ('b -> 'b) ;
|
|
holdFn = Just id ;
|