myPatterns: pattern matching in custom notations for Java & JavaScript

Nic Volanschi <>
Tue, 29 Jun 2010 20:43:16 +0200

          From comp.compilers

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myPatterns: pattern matching in custom notations for Java & JavaScript (Nic Volanschi) (2010-06-29)
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From: Nic Volanschi <>
Newsgroups: comp.compilers
Date: Tue, 29 Jun 2010 20:43:16 +0200
Organization: Compilers Central
Keywords: tools, lex, available
Posted-Date: 30 Jun 2010 09:50:34 EDT

I am looking for (feedback from) potential users of an open source
library for Java and JavaScript, called myPatterns, implementing a
new concept: pattern matching in "custom notations".

What are custom notations?

Everyone knows pattern matching of strings using regular expressions.
myPatterns implements a more general notion of pattern matching:
- working not only on strings, but on any program data: numbers,
    objects, collections, etc.
- using patterns written either in a pre-defined notation, subsuming
    regular expressions and JSON, on in user-defined notations.

When designing a class API, programmers using this library can also
design very easily a custom syntax for matching objects of that class,
i.e. for selecting objects of a certain shape, and decomposing them
into smaller pieces.

For more details, see



A balance method for red-black trees can be written very concisely
using a custom notation in which a red-rooted tree is written
"(left label right)" and a black-rooted tree is written
"[left label right]":

static final String pats[] = {"[((%a %x %b) %y %c) %z %d]",
                                                            "[(%a %x (%b %y %c)) %z %d]",
                                                            "[%a %x ((%b %y %c) %z %d)]",
                                                            "[%a %x (%b %y (%c %z %d))]"};

rbTree balance() {
        Subst s = Matchbox.matchAny(this, pats);
        if(s != null)
                return new rbTree(red,
                                                    new rbTree(black, (rbTree)s.get('a'),
                                                    new rbTree(black, (rbTree)s.get('c'),
        return this;

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