foreach on matrices (idea from BProlog)

library/examples/matrix.yap

@@ -1,5 +1,6 @@
 
 :- use_module(library(matrix)).
+:- use_module(library(maplist)).
 
 t1 :-
 	X <== matrix([1,2,3,4,5,6],[dim=[3,2]]),
@@ -27,3 +28,32 @@ numbers(I0, I1, Vals) :-
 	( I0 =< I1 -> Vals = [I0|MVals], I01 is I0+1, numbers(I01, I1, MVals) ;
 	    Vals = [] ).
 
+t5 :-
+	numbers(1, 100, L),
+	X <== matrix(L, [dim=[10,10]]),
+	writeln('diagonal:'),
+	foreach([I in 0..9, J in I..I], Y^(Y <== X[I,J], writeln(Y) ) ).
+t6 :-
+	Len = 10,
+	LenSq is Len*Len,
+	Len1 is Len-1,
+	numbers(1, LenSq, L),
+	X <== matrix(L, [dim=[Len,Len]]),
+	Y <== matrix(L, [dim=[Len,Len]]),
+	Z <== matrix(L, [dim=[Len,Len]]),
+	writeln('product:'),
+	foreach([I in 0..Len1, J in 0..Len1], step(X,Y,Z,I,J) ),
+	O <== list(Z),
+	writeln(O).
+
+step(X,Y,Z,I,J) :-
+	Xs <== X[I,_],
+	Ys <== Y[_,J],
+	foldl(addprod, Xs, Ys, 0, P), % scalar product
+	Z[I,J] <== P.
+
+addprod(X, Y, S0, S) :-
+	S is S0+X*Y.
+
+
+