Hi Alan,
My way of specifying syntax is outlined here:
http://www.romanredz.se/papers/CSP2009.Mouse.pdf
and described with all details here:
http://mousepeg.sourceforge.net/Mouse-1.2.manual.pdf
The main idea is to place semantic actions in a separate file (Java
class in this case), so that it does not obscure the grammar. The
grammar contains only the names of actions in curly brackets. This style
was used with yacc++ by my colleague Bertil Steinholtz to produce very
clear code. He could also use different semantic files to produce
different semantics for the same grammar.
-- Roman
On 2010-11-15 15:32, Alan Post wrote:
I'm implementing a packrat parser in Scheme. I'm at the point of
writing a bootstrap parser in Scheme for PEG, and my bootstrap
parser is basically working.
I haven't yet decided on the syntax for embedding code in the
parser. My only example for doing this is peg/leg:
http://piumarta.com/software/peg/peg.1.html
which encloses code in {} brackets and permits references to parts
of the parse tree with<>:
{ action }
Curly braces surround actions. The action is arbitray C source
code to be executed at the end of matching. Any braces within
the action must be properly nested. Any input text that was
matched before the action and delimited by angle brackets (see
below) is made available within the action as the contents of
the character array yytext. The length of (number of characters
in) yytext is available in the variable yyleng. (These variable
names are historical; see lex(1).)
< An opening angle bracket always matches (consuming no input) and
causes the parser to begin accumulating matched text. This text
will be made available to actions in the variable yytext.
> A closing angle bracket always matches (consuming no input) and
causes the parser to stop accumulating text for yytext.
What else is out there? Is this something reasonably standard or does
every tool do something different?
-Alan
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