On Dec 7, 2009, at 4:28 PM, Kevin Curtis wrote:
(This is as considered separately from the possibility of
programatically
manipulating a parsed AST - the use cases for that are clear.
Though there
may still be verification issues depending on the nature of the
manipulation
API. It seems like the possibilities are either specialized objects
that
enforce validity on every individual manipulation, or something
that accepts
JSON-like objects and verifies validity after the fact, or
something that
accepts JSON-like objects and verifies validity by converting to
JavaScript
source code and then parsing it).
Regards,
Maciej
I asked something similar here:
https://mail.mozilla.org/pipermail/es-discuss/2009-May/009243.html
Are there 2 approaches to adding AST functionality in ecmascript:
1) The AST as JSON
Either Brendan's original example or the S-expression-ish jsonml.
This covers both the in memory representation of the AST and its
serialization format.
I withdrew my sketch in favor of the JsonML direction back in the
original thread.
2) API
Similar to the ast module in python where multiple api calls build the
AST nodes.
----
Given that there are no takers for 'scheme by the back door', then,
with the object hardening features of ES5 - 2) should be considered.
e.g:
// assume an ast module factory
var x = ast.BinOp("+", 4, 5);
x.left = 6;
x.right = 7
x.whatever = 8 // error
The Python ast module has a dump method which dumps the AST tree of
Python objects to a string of nested functions calls - which can be
eval'ed to recreate in memory.
As I think David-Sarah just pointed out, using too much memory to
express something that can be encoded in a much smaller string can be
a bit of a lose.
Standardized ASTs are not a done deal, they constitute a prior work
item, call it 0. We should check whether it is something TC39 members
could agree on in more detail before going too far, although some
popular implementations and a bit of luck not over-constraining parser
implementation choices could lead to adoption and de-facto
standardization.
/be
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