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

Patricia Shanahan <>
Sun, 26 Aug 2007 13:10:41 -0700
Ulrich Scholz wrote:

On 26 Aug., 17:08, Patricia Shanahan <> wrote:

Ulrich Scholz wrote:

I enjoy programming (and thinking) in Prolog but the reality requires
Java. Now I try to use the best of the former with the latter.

Thanks for your answers. You're probably right in saying that trying
to program Prolog-style in Java will lead to bad programs.

Nevertheless, I have a problem with many (~20) cases where any case
that "matches" has to be considered. (More precisely, it's a fix
point computation with an initial situation, which is extended each
time a case "matches". But the kind of computation should not matter
here.) "Matching" corresponds to the success of all of a small set of
tests, like {a>5, t is the empty string, p is not null}.

If you say: Don't do it the Prolog way, do it the Java way instead:
What is the Java way?


I'm not sure I understand your problem well enough for a complete
solution, but here is one idea of how I might approach it. Even if this
is not right for your problem, it may give you some bits and pieces of
ideas that help.

interface Matcher{
   boolean matches(int a, String t, Object p);

Obviously, the parameters are just examples. Possibly there is some
object describing the current solution.

Then write an array of Matcher objects:

Matcher example1 = new Matcher(){
   public boolean matches(int a, String t, Object p){
     return a>5 && "".equals(t) && p != null;

Matcher example2 = new Matcher(){
   public boolean matches(int a, String t, Object p){
     return a>=42;

Stick references to these in an array or List:

Matcher[] allMatchers = {

Apply them in a loop:

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


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