view lib/ur/option.ur @ 883:467285bb5578

Avoid preparing the same statement twice
author Adam Chlipala <adamc@hcoop.net>
date Fri, 17 Jul 2009 13:19:41 -0400
parents 0d30e6338c65
children da3ec6014d2f
line wrap: on
line source
datatype t = datatype Basis.option

fun eq [a] (_ : eq a) =
    mkEq (fn x y =>
             case (x, y) of
                 (None, None) => True
               | (Some x, Some y) => x = y
               | _ => False)

fun isSome [a] x =
    case x of
        None => False
      | Some _ => True

fun mp [a] [b] f x =
    case x of
        None => None
      | Some y => Some (f y)

fun bind [a] [b] f x =
    case x of
        None => None
      | Some y => f y