Predicate Specification

A couple of notes on how to specify your predicates in DeepWeaver, that are worth mentioning because they're different from how they're specified in Prolog.

When you're specifiying a predicate there are a number of reserved keywords, and an few restrictions.

name(fn,sn)=getName(fn,sn);

This is the basic standard specification, fn and sn are bound or unbound variables of any type.

name(in fn, out sn)=getName(fn,sn);

This restricts the standard specification, because fn must be bound and sn must be unbound when this predicate is called, otherwise it will be ignored. You could overload is by following it with the first example above.

name(String fn, out sn)=getName(fn,sn);

Now fn must be a String object, but may be bound or unbound, sn must still be unbound.

Points of note:

• Unless your variable name is one char long, it should start with a small letter or it will be mistaken for a type binding
• in and out should not be used as variable names
• Predicates can be overloaded, but they are overloaded in order (same as Prolog), meaning that if you have a predicate which has no binding or type restrictions, it should be the final specified predicate
• No error will be thrown if your bindings cause a predicate call that you did not expect
  

Modifications of standard Prolog

Deepweaver changes a number of standard Prolog syntactical features to bring it closer to Java, and make pattern cuts more familiar to Java developers

Declaring a predicate is no longer done using the Prolog iff term :-, instead the = symbol is used.
Terminating a predicate is no longer performed using the fullstop symbol . instead the semicolon is used ; Since the semicolon in Prolog represents or, this has now been replaced with the pipe character, |
Comments are now of standard Java form, so instead of % we have // for single line comments and /* .. */ for multiline comments
Negation is slightly different from standard Prolog in that \+ is no longer used to reperesent negation, instead use the not(A) predicate.

Finally, its worth noting that in a .dw file, only predicates preceeded by a question mark will be executed. One should declare all the required predicates and then select the one to be executed by writing ?runMe(A,B); at the end of the file.

eg. well_located(A,B) = statement(A,X), not(between(s, X, B, true));