:- module map_impl.

:- interface.

:- import_module list.

:- pred map_rev(list(list(T))::in, list(list(T))::out) is det.

:- pred map_reduce_add(list(list(int))::in, list(int)::out) is det.

:- implementation.

:- import_module int.

map_reduce_add(L, R) :-
	mymap(reduce_add, L, R).

map_rev(L, R) :- mymap(rev, L, R).

:- pred mymap(pred(T, U), list(T), list(U)).
:- mode mymap(pred(in, out) is det, in, out) is det.
  
mymap(_P,[],[]).
mymap(P,[H|T],[PH|PT]) :-
        call(P,H,PH),
        mymap(P,T,PT).

:- pred reduce_add(list(int)::in, int::out) is det.
reduce_add(List,Res) :-
        reduce(add,0,List,Res).

:- pred add(int::in, int::in, int::out) is det.
add(X,Y,Z) :-
        Z is X + Y.


:- pred reduce(pred(U, T, T), T, list(U), T).
:- mode reduce(pred(in, in, out) is det, in, in, out) is det.

reduce(_Func,Base,[],Base).
reduce(Func,Base,[H|T],Res) :-
        reduce(Func,Base,T,TRes),
        call(Func, H, TRes, Res).

:- pred rev(list(T)::in, list(T)::out) is det.
rev(L,R) :-
        rev(L,[],R).

:- pred rev(list(T)::in, list(T)::in, list(T)::out) is det.
rev([],L,L).
rev([H|T],A,R) :-
        rev(T,[H|A],R).