17.5: Implementation Notes by Vassili Bykov

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What to look at first. In 90% of the cases, the method String>>matchesRegex: is all you need to access the package.

RxParser accepts a string or a stream of characters with a regular expression, and produces a syntax tree corresponding to the expression. The tree is made of instances of Rxs* classes.

RxMatcher accepts a syntax tree of a regular expression built by the parser and compiles it into a matcher: a structure made of instances of Rxm* classes. The RxMatcher instance can test whether a string or a positionable stream of characters matches the original regular expression, or it can search a string or a stream for substrings matching the expression. After a match is found, the matcher can report a specific string that matched the whole expression, or any parenthesized subexpression of it. All other classes support the same functionality and are used by RxParser, RxMatcher, or both.

Caveats The matcher is similar in spirit, but not in design to Henry Spencer’s original regular expression implementation in C. The focus is on simplicity, not on efficiency. I didn’t optimize or profile anything. The matcher passes H. Spencer’s test suite (see test suite protocol), with quite a few extra tests added, so chances are good there are not too many bugs. But watch out anyway.

Acknowledgments Since the first release of the matcher, thanks to the input from several fellow Smalltalkers, I became convinced a native Smalltalk regular expression matcher was worth the effort to keep it alive. For the advice and encouragement that made this release possible, I want to thank: Felix Hack, Eliot Miranda, Robb Shecter, David N. Smith, Francis Wolinski and anyone whom I haven’t yet met or heard from, but who agrees this has not been a complete waste of time.