Structure Option
(* Option -- SML Basis Library *)
exception Option
datatype option = datatype option
val getOpt : 'a option * 'a -> 'a
val isSome : 'a option -> bool
val valOf : 'a option -> 'a
val filter : ('a -> bool) -> 'a -> 'a option
val map : ('a -> 'b) -> 'a option -> 'b option
val app : ('a -> unit) -> 'a option -> unit
val join : 'a option option -> 'a option
val compose : ('a -> 'b) * ('c -> 'a option) -> ('c -> 'b option)
val mapPartial : ('a -> 'b option) -> ('a option -> 'b option)
val composePartial : ('a -> 'b option) * ('c -> 'a option) -> ('c -> 'b option)
(*
[getOpt (xopt, d)] returns x if xopt is SOME x; returns d otherwise.
[isSome vopt] returns true if xopt is SOME x; returns false otherwise.
[valOf vopt] returns x if xopt is SOME x; raises Option otherwise.
[filter p x] returns SOME x if p x is true; returns NONE otherwise.
[map f xopt] returns SOME (f x) if xopt is SOME x; returns NONE otherwise.
[app f xopt] applies f to x if xopt is SOME x; does nothing otherwise.
[join xopt] returns x if xopt is SOME x; returns NONE otherwise.
[compose (f, g) x] returns SOME (f y) if g x is SOME y; returns NONE
otherwise. It holds that compose (f, g) = map f o g.
[mapPartial f xopt] returns f x if xopt is SOME x; returns NONE otherwise.
It holds that mapPartial f = join o map f.
[composePartial (f, g) x] returns f y if g x is SOME y; returns NONE
otherwise. It holds that composePartial (f, g) = mapPartial f o g.
The operators (map, join, SOME) form a monad.
*)
Moscow ML 2.00