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prologclpfd

Swi-Prolog asserta error

i must assert in SWI this kind of CLP(FD) rules: 

    asserta(schedule(A,B) :-  V = [S0,S1,S2],V ins 0..sup).

but i get this error:

    ERROR: Syntax error: Operator expected
    ERROR: asserta(schedule(A,B) :-  V = [S0,S1,S2],V 
    ERROR: ** here **
    ERROR: ins 0..sup) .

why? thank you!

Solution

  • There are two errors here:

    You need to have CLP(FD) loaded at the time when reading the text. So there needs to be a use_module(library(clpfd)) either as a directive like in a line

    :- use_module(library(clpfd)).

    or entered as a goal on the toplevel. This is necessary because you are using (ins)/2 in operator form.

    The other problem is the missing parentheses. It should rather read:

     ..., asserta( ( schedule(A,B) :- V = [_,_,_], V ins 0..sup ) ), ...

    As an aside, I do not think that asserting such a rule makes much sense. Dynamic databases are rarely used together with asserting rules as this one.