Data commit

Task/Stack/Mercury/stack.mercury

@@ -0,0 +1,33 @@
+:- module sstack.
+
+:- interface.
+
+% We're going to call the type sstack (simple stack) because we don't want to get it
+% accidentally confused with the official stack module in the standard library.
+:- type sstack(T).
+
+:- func sstack.new = sstack(T).
+:- pred sstack.is_empty(sstack(T)::in) is semidet.
+:- func sstack.push(sstack(T), T) = sstack(T).
+:- pred sstack.pop(T::out, sstack(T)::in, sstack(T)::out) is semidet.
+
+:- implementation.
+
+:- import_module list.
+
+:- type sstack(T)
+   --->  sstack(list(T)).
+
+sstack.new = sstack([]).
+
+sstack.is_empty(sstack([])).
+
+sstack.push(Stack0, Elem) = Stack1 :-
+   Stack0 = sstack(Elems),
+   Stack1 = sstack([Elem | Elems]).
+
+sstack.pop(Elem, !Stack) :-
+   !.Stack = sstack([Elem | Elems]),
+   !:Stack = sstack(Elems).
+
+:- end_module sstack.