Re: Constraints in Ciao Prolog - Ciao-users

13 Dec 2001


      Dear Alexandre,
No, CLP(Q/R) in Ciao is not the same as the IBM's clpr.
The main difference is that in Ciao the constraints can only be imposed
by a constraint builtin, there is no implicit constraint resolution in
the unification.  Just compare the Fibonacci function in IBM's clpr
fib(0, 1).
  fib(1, 1).
  fib(N, X1 + X2) :-
          N > 1,
          fib(N - 1, X1), 
          fib(N - 2, X2).
and in Ciao's CLP(Q/R)
fib(X,Y):- X .=. 0, Y .=. 0.
  fib(X,Y):- X .=. 1, Y .=. 1.
  fib(N,F) :-
          N .>. 1,
          N1 .=. N - 1,
          N2 .=. N - 2,
          fib(N1, F1),
          fib(N2, F2),
          F .=. F1+F2.
The Ciao version is more "verbose", but in turn its semantics is well
defined, can be extented to other constraint domains, and allows mixing
traditional Prolog code with CLP code.  This and other examples can be
found in library/clpqr_src/examples from the Ciao main directory.  The
files ending in .clp are the original examples in IBM's clpr.
Daniel