view demo/list.ur @ 615:3c77133afd9a

Start of Featherweight Ur semantics
author Adam Chlipala <adamc@hcoop.net>
date Tue, 17 Feb 2009 14:49:28 -0500
parents 7ef4b2911b09
children 669ac5e9a69e
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line source
datatype list t = Nil | Cons of t * list t

fun length (t ::: Type) (ls : list t) =
    let
        fun length' (ls : list t) (acc : int) =
            case ls of
                Nil => acc
              | Cons (_, ls') => length' ls' (acc + 1)
    in
        length' ls 0
    end

fun rev (t ::: Type) (ls : list t) = 
    let
        fun rev' (ls : list t) (acc : list t) =
            case ls of
                Nil => acc
              | Cons (x, ls') => rev' ls' (Cons (x, acc))
    in
        rev' ls Nil
    end