Parsing of heredoc syntax / matching captured strings

[Guilherme Vieira]

Hi,

I'm trying to parse PHP code and I'm bumping into issues with heredocs. I'm wondering how can I parse them. I need a way to match a string that has been previously matched.

Is this possible with PEG.js?

--

Atenciosamente / Sincerely,
Guilherme Prá Vieira

[Zak Greant]

Dear Guilherme,

On 2013-03-04, at 14:29, Guilherme Vieira <n2.ni...@gmail.com (mailto:n2.ni...@gmail.com)> wrote:
...

> I'm trying to parse PHP code and I'm bumping into issues with heredocs. I'm wondering how can I parse them. I need a way to match a string that has been previously matched.

…

You can use the & { predicate } expression for this (see http://pegjs.majda.cz/documentation for more details.)

Here's a basic example:

{ Array.prototype.f = function( glue ){ return this.join( glue || '' ); } }

start
= heredoc:( s:('<<<' hid __) l:line* e:(hid ';') {return {start:s.f(), content:l.f(), end:e.f()} })
& {return heredoc.start.slice(3,-1) == heredoc.end.slice(0,-1) && -1 == heredoc.content.indexOf( "\n" + heredoc.end );}
{return heredoc;}

__ = "\n"
chr = [^\n]
hid = c:[a-z]i+ {return c.f();}
line = c:chr* __ {return c.f() + "\n";}
lines = l:line+ {return l.f();}


Cheers!
--zak

[David Majda]

Hi,

2013/3/4 Guilherme Vieira <n2.ni...@gmail.com>

I'm trying to parse PHP code and I'm bumping into issues with heredocs. I'm wondering how can I parse them. I need a way to match a string that has been previously matched.

Is this possible with PEG.js?

Have a look at the DelimitedBodyVariable rule in this parser to see how I solved it:

  https://github.com/apiaryio/blueprint-parser/blob/v0.4.3/src/apiary-blueprint-parser.pegjs#L319 

A cleaner solution would be to use some kind of backreferences, but PEG.js doesn't support them (at least not yet -- I am considering adding them).

P.S.: Zak's solution mentioned in the other reply to your mail won't work, because the "*" operator does not backtrack, so the "line*" expression in his grammar will match all remianing lines of the input regardless on whether the terminator was encountered or not.

--
David Majda
Entropy fighter
http://majda.cz/

[lon...@gmail.com]

This is nice approach in that the opening and closing tokens for the "HERE" document are not fixed (the keyword "<<<" is) and the user can use their own choice.

Note that if you use the parser actions in node.js with "use strict" then you must also add a ```{ var bodyTerminal; }``` initializer at the start of the grammar so that the global bodyTerminal variable is exposed between parser action blocks.