Mercurial > urweb

annotate tests/type_class.ur @ 674:fab5998b840e

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
Type class reductions, but no inclusions yet
author Adam Chlipala <adamc@hcoop.net>
date Thu, 26 Mar 2009 14:37:31 -0400
parents 71bafe66dbe1
children 43430b7190f4
rev   line source
adamc@674 1 datatype pair a b = Pair of a * b
adamc@211 2
adamc@674 3 structure M : sig
adamc@674 4 class default
adamc@674 5 val get : t ::: Type -> default t -> t
adamc@211 6
adamc@674 7 val string_default : default string
adamc@674 8 val int_default : default int
adamc@212 9
adamc@674 10 val option_default : t ::: Type -> default t -> default (option t)
adamc@674 11 val pair_default : a ::: Type -> b ::: Type -> default a -> default b -> default (pair a b)
adamc@674 12 end = struct
adamc@674 13 class default t = t
adamc@674 14 fun get (t ::: Type) (x : t) = x
adamc@212 15
adamc@674 16 val string_default = "Hi"
adamc@674 17 val int_default = 0
adamc@674 18
adamc@674 19 fun option_default (t ::: Type) (x : t) = Some x
adamc@674 20 fun pair_default (a ::: Type) (b ::: Type) (x : a) (y : b) = Pair (x, y)
adamc@674 21 end
adamc@674 22
adamc@674 23 open M
adamc@674 24
adamc@674 25 fun default (t ::: Type) (_ : default t) : t = get
adamc@674 26 val hi : string = default
adamc@674 27 val zero : int = default
adamc@674 28 val some_zero : option int = default
adamc@674 29 val hi_zero : pair string int = default
adamc@674 30
adamc@674 31 fun frob (t ::: Type) (_ : default t) : t = default
adamc@674 32 val hi_again : string = frob
adamc@674 33 val zero_again : int = frob
adamc@674 34
adamc@674 35 fun show_option (t ::: Type) (_ : show t) : show (option t) =
adamc@674 36 mkShow (fn x =>
adamc@674 37 case x of
adamc@674 38 None => "None"
adamc@674 39 | Some y => show y)
adamc@674 40
adamc@674 41 fun show_pair (a ::: Type) (b ::: Type) (_ : show a) (_ : show b) : show (pair a b) =
adamc@674 42 mkShow (fn x =>
adamc@674 43 case x of
adamc@674 44 Pair (y, z) => "(" ^ show y ^ "," ^ show z ^ ")")
adamc@674 45
adamc@674 46 fun main () : transaction page = return <xml><body>
adamc@674 47 {[hi_again]}, {[zero_again]}, {[some_zero]}, {[hi_zero]}
adamc@674 48 </body></xml>