Hi Claus. Yes I would be very interested in your extensions. Thanks for
the pointers below.
My code is now available on github (JS parser combinators and a
grammar edging closer to ES5, an AST with unparsing support; an
experiment beyond ES5 is included as an example, by translating
new syntax for paren-free function calls/definitions to old syntax):
https://github.com/clausreinke/jstr
Please consider this a semi-public preview, there is still much to do
and many of the comments are notes to self rather than user docs.
I took the liberty of adding most of a SpiderMonkey-style AST
(there are still some unwanted deviations, as well as a few items
needing clarification, so you wont be able to port your code just
yet). It turns out that this AST spec is biased towards evaluation,
so I needed to augment it to support proper unparsing.
As I said, I've got a long and growing TODO list, but if there are
any particular improvements/fixes that would help you or others
here, knowing about them would influence my priorities.
Thanks for your interest,
Claus
________________________________
From: Claus Reinke <claus.rei...@talk21.com>
To: Kam Kasravi <kamkasr...@yahoo.com>
Cc: es-discuss <es-discuss@mozilla.org>
Sent: Wednesday, June 1, 2011 6:48 AM
Subject: Re: ES parsing tools (Re: Short Functions)
Hi Kam,
I've been experimenting with pegjs - which generates a parser based on
the ecma-262 5th edition grammar.
yes, pegjs [1] and jsparse [2] were the alternatives I had been looking
at. pegjs is probably a bit ahead when you just want to use the parse
result; I chose to build on jsparse because it gives me more flexibility
for grammar-level experimentation (no fixed barrier between grammar and
grammar processor).
pegjs comes with a fairly complete transliteration of the ES5 grammar,
but you should give it a look-over for PEG vs LR issues (jsparse and
ometa have similar issues): a PEG parser will commit to a choice
alternative locally, even where the grammar was written with the
implicit requirement of a 1 token lookahead for parsing.
Typical example, in Statement:
ExpressionStatement / LabelledStatement
For input "id \n : 1", a PEG parser will commit to the first branch
after successfully parsing an Identifier and inserting a semicolon,
without ever checking whether the next token is ':' (this assumes
the usual local and explicit implementation of ASI, instead of the
implicit error correction with 1 token lookahead required by the
ASI spec; which is global in that it depends on the whole grammar).
Apart from fixing some such issues in jsparse, I've moved its grammar
closer to ES5 (not complete, but can parse code like fulljslint.js or the
ASI-reliant read-json.js [3] from node's npm, mentioned in an earlier
thread here), added parse error messages and grammar debugging help
(grammar rule tracing and rule stack record).
I've been building a backend that walks the ast to regenerate the code
(less white related formatting).
The nice thing about pegjs is most of the ast nodes agree with the parser
api (https://developer.mozilla.org/en/SpiderMonkey/Parser_API)
My approach is to add various strawmen and have them translated to plain
javascript - transpiler approach.
I've been very happy with the ast it generates thus far.
Thanks for the reminder. There actually is a strawman for parser
API standardization:
http://wiki.ecmascript.org/doku.php?id=strawman:ast
Sadly, that isn't in Harmony yet (oversight, or decision?) but if
everyone here agrees on the general format, I'd add it as an
option to my parser. If would be good to agree on how to
preserve whitespace and comments (essential for source to
source transformations).
Claus
[1] http://pegjs.majda.cz/
[2] http://github.com/doublec/jsparse
(my own extensions to Chris' work are not online yet,
but I could make a snapshot available if there is interest)
[3] https://github.com/isaacs/npm/blob/master/lib/utils/read-json.js
(a useful ASI-reliant parser test case)
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