From: Eric Mahurin <eric.mahurin@...>
Date: 2005-11-05T01:35:52+09:00
Subject: Re: YACC (Was: Re: ruby-dev summary 27393-27541)

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On 11/4/05, daz <dooby@d10.karoo.co.uk> wrote:
>
> (1997-11-28) - Chris F Clark
> http://compilers.iecc.com/comparch/article/97-11-150
>
> "Unfortunately, most parsing systems don't encourage
> thinking about parsing as sequences of transformations.
> Instead they promote the view of one lexer and one parser."


BTW, in my grammar project, I do think of parsing as sequences of
transformations. A lexer simply transforms a sequence of characters to a
token sequence. A parser transforms a sequence of tokens to an AST (or
whatever) sequence. With my system, you could easily make a lexer-free
parser (parse directly from characters) or go the other way and add more
transformation stages (i.e. a preprocessor). For example, I made a TCL
interpreter that required no lexer (the simplicity and no keywords helps a
lot). Or on the other extreme, you could envision a C compiler built with a
series of transformations: preprocess -> tokenize -> parse -> optimize ->
assembly -> machine code. My Grammar classes don't care what type of input
and output they make - an extreme unification of lexing, parsing, AST
parsing, etc.

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