tasks a-s

Task/Order-two-numerical-lists/Mercury/order-two-numerical-lists-1.mercury

@@ -0,0 +1,3 @@
+:- pred lt(list(int)::in, list(int)::in) is semidet.
+lt([], [_|_]).
+lt([H1|T1], [H2|T2]) :- H1 =< H2, T1 `lt` T2.

Task/Order-two-numerical-lists/Mercury/order-two-numerical-lists-2.mercury

@@ -0,0 +1,3 @@
+:- pred lt(list(T)::in, list(T)::in) is semidet <= comparable(T).
+lt([], [_|_]).
+lt([H1|T1], [H2|T2]) :- H1 =< H2, T1 `lt` T2.

Task/Order-two-numerical-lists/Mercury/order-two-numerical-lists-3.mercury

@@ -0,0 +1,27 @@
+:- module comparable.
+:- interface.
+:- import_module int, float, integer, list.
+
+:- typeclass comparable(T) where [
+        pred '<'(T::in, T::in) is semidet,
+        pred '=<'(T::in, T::in) is semidet
+].
+:- instance comparable(int).
+:- instance comparable(float).
+:- instance comparable(integer).
+:- instance comparable(list(T)) <= comparable(T).
+
+:- implementation.
+
+:- instance comparable(int) where [
+        pred('<'/2) is int.(<),
+        pred('=<'/2) is int.(=<)
+].
+% likewise for float and integer...
+:- instance comparable(list(T)) <= comparable(T) where [
+        pred('<'/2) is lt,   % the 'lt' above.
+        pred('=<'/2) is lte  % 'lt' with: lte([], []).
+].
+
+% pred lt
+% pred lte

Task/Order-two-numerical-lists/Mercury/order-two-numerical-lists-4.mercury

@@ -0,0 +1,6 @@
+:- pred test(list(T), list(T), io, io) <= comparable(T).
+:- mode test(in, in, di, uo) is det.
+test(A, B) -->
+        io.write(A), io.write_string(" < "), io.write(B),
+        io.write_string(" : "), io.write_string(S), io.nl,
+        { A < B -> S = "yes" ; S = "no" }.