(* // This file is for Assignment 4, BU CAS CS 520, Fall, 2009 // // Instructor: Hongwei Xi (hwxi AT cs DOT bu DOT edu) // *) (* ****** ****** *) // // Here is some code that you may want to study when doing Exercise 1 // (* ****** ****** *) // // How to compile: // atscc -o test exercise1.dats // // How to test: // ./test // (* ****** ****** *) abst@ype T typedef List = {X:type} (X, (T, X) - X) - X // end of [List] val Nil = lam{X:type} (nil:X, cons: (T, X) - X) = nil val Cons = lam (x: T, xs: List) = lam{X:type} (nil:X, cons: (T, X) - X) = cons (x, xs{X}(nil, cons)) // end of [fun] (* ****** ****** *) extern fun List_append (xs: List, ys: List):<> List (* please put your code here *) (* ****** ****** *) extern fun List_reverse (xs: List):<> List (* please put your code here *) (* ****** ****** *) assume T = int (* ****** ****** *) typedef int = intptr val _0 = intptr_of_int 0 val _1 = intptr_of_int 1 fn List_length (xs: List):<> int = xs {int} (_0, lam (_x, _xs) => _xs + _1) (* ****** ****** *) fn list_of_List (xs: List): list0 T = let typedef X = list0 T val nil = list0_nil : X val cons = lam (_x: T, _xs: X) = list0_cons (_x, _xs) in xs {X} (nil, cons) end // end of [list_of_List] (* ****** ****** *) fn List_print (xs: List): void = let val nil = unit () val cons = lam (_x: T, _xs: unit) = \$effmask_all (print _x; print_newline (); _xs) val unit () = xs {unit} (nil, cons) in // nothing end // end of [List_print] (* ****** ****** *) val xs123 = Cons (1, Cons (2, Cons (3, Nil))) : List val () = begin print "length of xs123 = "; print (List_length xs123); print_newline () end // end of [val] val () = print "xs123 =\n" val () = List_print xs123 val xs321 = List_reverse (xs123) val () = print "xs321 =\n" val () = List_print xs321 val xs123123 = List_append (xs123, xs123) val () = print "xs123123 =\n" val () = List_print xs123123 (* ****** ****** *) implement main () = () (* ****** ****** *) (* end of [exercise1.dats] *)