Re: Backtracking parsers

Michael Lee Finney <>
30 Jun 2000 00:50:47 -0400

          From comp.compilers

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From: Michael Lee Finney <>
Newsgroups: comp.compilers
Date: 30 Jun 2000 00:50:47 -0400
Organization: (
References: 00-05-111 00-05-119 00-06-015 00-06-032 00-06-037 00-06-063
Keywords: parse says...
> A couple of thoughts:
> If the symbols in the pattern have no meaning individually, then the
> language is no more than a regular expression.
> If, OTOH, constituent clauses of the sentence [may] have individual
> meaning, but the meaning of the composition changes when they are
> individually recognized, then you've kicked the whole system up into a
> realm where symbols are [for lack of term] "imagery", a "clause" is an
> "idea", and "sentence" is a composition of ideas.

A regular expression defines a language over a set of symbols such
that the rewriting rules have certain restrictions. However, no
language requires that the individual symbols have any "meaning"
whatsoever, even those which are not regular expressions (which is
most of them).

> At this point, a "sentence" looks a lot like a paragraph in a human
> language. However, in a human language, a paragraph typically
> represents a set of related ideas, whereas in a computer oriented
> language, a sentence typically expresses a single idea.

Usually, but not always. People "pun" in computer languages as well,
although I cannot bring a particular instance to mind at the moment.

> Recognizing that this was an academic question to begin with, what
> would be the utility of machine recognition of such a language?

This is not an entirely academic question, but a point in a discussion
about how to specify grammars.

> Humans can't agree on what human languages mean ... would you expect
> the machine experience with such a language to be different?

Except in the natural language arena, I certainly do expect computers to
"agree" on what a particular grammar means unless it is ambiguous.

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