> Hello everyone,
> I had a problem with ':' in the developement of expert shell in SWI
> KNOWLEDGE BASE
> :- op(900,xfx,':').
> :- op(880,xfx,then).
> :- op(870,fx,if).
> :- op(550,xfy,or).
> rule : if a or b or c or d or e then problem.
> %% Note the ':'
> END KNOWLEDGE BASE
> c:/pl/test.pl compiled 0.00 sec, 1,088 bytes
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> 1 ?- listing.
> 2 ?-
> This shows no rule.
> If we replace ':' by any other atom it gives proper result.
> Does any thing wrong with ':' ?
> Please, can any one give me the solution on it to use in SWI ?
Two issues here:
1. do you really want to give your rules directly to the Prolog
compiler? The Prolog compiler will just take them as a collection
of facts (for the predicate :/2 or then/2, see below).
I find it more likely that you will need a sort or rule-compiler,
i.e. a program that reads your rules as data structures, and
transforms them into something more useful (like a decision tree).
Such a program would use e.g. read/2 to read the rules, and in
that case you will not have any problem with using the colon,
because _your_ program decides what the colon means.
2. If you give your rules to a Prolog compiler with a Quintus-style
module system (as you have done), the colon will be interpreted as
a module qualification. So your example rule is taken as a fact for
the predicate then/2 in module 'rule', because it is equivalent to
rule:then(if(or(a, or(b, or(c, or(d, e))))), problem)).
Prolog compilers that don't treat the colon specially will take it
as a fact for :/2 instead, but that probably clashes with the name
of a built-in predicate. So you should either choose a different
functor, or change the precedences such that the colon is not the
However, i really think you do not want to compile these rules as
facts at all.