CODEWITHSUNDEEP
prolog
user3444787
user3444787

Reputation: 25

Compare triangles in Prolog

I'm trying to compare two triangles by two point and height.

compare_tri( triangle ( point(X1,Y1), point(X2,Y2), H1),
    triangle( point(X3,Y3), point(X4,Y4), H2)) :-
    A1 is ((X2-X1)*(X2-X1)),
    B1 is ((Y2-Y1)*(Y2-Y1)),
    C1 is (A1+B1),
    D1 is (sqrt(C1)),
    S1 is (D1*H1),
    A2 is ((X4-X3)*(X4-X3)),
    B2 is ((Y4-Y3)*(Y4-Y3)),
    C2 is (A2+B2),
    D2 is (sqrt(C2)),
    S2 is (D2*H2),
    (  (S1 < S2)
    -> (S1 is 2), (S2 is 1)
    ;  (S2 is 2), (S1 is 1)
    ),
    write(S1), write('bigger than '), write(S2).

but I get the error message 'syntax operator : operator expected'

What's the problem?

Upvotes: 1

Views: 403

Answers (2)

CapelliC
CapelliC

Reputation: 60034

apart the syntax error, already addressed by Sergey, a general advice: attempt to write reusable code in first place. It's easier to debug, to read, to remember....

triangle_area(triangle(point(X1,Y1), point(X2,Y2), H), S1) :-
 A1 is ((X2-X1)*(X2-X1)),
 B1 is ((Y2-Y1)*(Y2-Y1)),
 C1 is (A1+B1),
 D1 is (sqrt(C1)),
 S1 is (D1*H1).

compare_tri(T1,T2) :-
 triangle_area(T1,S1),
 triangle_area(T2,S2), etc etc...

Upvotes: 0

Sergii Dymchenko
Sergii Dymchenko

Reputation: 7229

There must be no space between triangle and next brace: change triangle ( point(X1,Y1) to triangle( point(X1,Y1) and the error will be gone.

Upvotes: 1

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