Data.Maybe

Operations over Option.

The type is wired in; the prelude opens this module, so these are in unqualified scope everywhere.

Functions and Values

is_some : forall a. (Option(a)) -> Bool

True when the option holds a value.

is_none : forall a. (Option(a)) -> Bool

True when the option is empty.

unwrap_or : forall a. (a, Option(a)) -> a

The contained value, or the default d when the option is empty.

unwrap_or(0, Some(5))

map_option : forall e0 a b. ((b) -> a ! {e0}, Option(b)) -> Option(a) ! {e0}

Apply f to the contained value, leaving None untouched.

The default d here is not an option, so this example is rejected:

unwrap_or(0, 5)

and_then : forall e0 a b. ((a) -> Option(b) ! {e0}, Option(a)) -> Option(b) ! {e0}

Chain an option-returning function, short-circuiting on None (monadic bind for Option).

map_or : forall e0 a b. (a, (b) -> a ! {e0}, Option(b)) -> a ! {e0}

option_or : forall a. (Option(a), Option(a)) -> Option(a)

option_to_list : forall a. (Option(a)) -> List(a)

both : forall a b. (Option(a), Option(b)) -> Option((a, b))

option_fold_r : forall e0 a b. ((a, b) -> b ! {e0}, b, Option(a)) -> b ! {e0}

option_fold_l : forall e0 a b. ((a, b) -> a ! {e0}, a, Option(b)) -> a ! {e0}

option_bind : forall e0 a b. (Option(a), (a) -> Option(b) ! {e0}) -> Option(b) ! {e0}

option_ap : forall e0 a b. (Option((b) -> a ! {e0}), Option(b)) -> Option(a) ! {e0}