Re: Prolog-style pattern matching in Java. How to?

From:

Ulrich Scholz <d5@thispla.net>

Newsgroups:

comp.lang.java.programmer

Date:

Mon, 27 Aug 2007 01:55:10 -0700

Message-ID:

<1188204910.689829.240720@w3g2000hsg.googlegroups.com>

On Aug 26, 11:01 pm, Patricia Shanahan <p...@acm.org> wrote:

Hunter Gratzner wrote:

On Aug 26, 10:10 pm, Patricia Shanahan <p...@acm.org> wrote:

Apply them in a loop:

for(Matcher m: allMatchers){
if(m.matches(whatever parameters)){
// Deal with a hit

Better, let the "matcher" deal with the hit => Visitor

interface Visitor {
   public void visit(Computation c);
}

Visitor example1 = new Visitor() {
   public void visit(Computation c) {
      if(c.getA() > 5 && "".equals(c.getT()) && c.getP() != null) {
         // manipulate Computation c in some way
         // c.setX(...); c.setY(...);
      }
   }
}

I would make the choice between the two approaches depending on how the
reaction to a match depends on the pattern. If there is a fixed
reaction, then the matcher should just decide whether there is a match.
If a match condition and a reaction to it are logically coupled, then
the visitor pattern is better.

Patricia

Thanks again for your helpful and constructive answers. I'll let them
sink in.

Ulrich