Generating a pretty AST with LPeg
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- Subject: Generating a pretty AST with LPeg
- From: Matthias Kluwe <mkluwe@...>
- Date: 2014年1月29日 10:41:30 +0000 (UTC)
Hi!
I've nearly finished my first parsing task using LPeg (which was parsing
SAS-code to visualize the "data flow") and it was fun.
As I'm lacking some experience my "AST" resulting from the parsing step
is not too pretty. Let me give you a simplified example of what my "AST"
looks now. Consider parsing "function calls" in some hypothetical
language:
Using
local WS = lpeg.S' \n\t'^0
local NAME = lpeg.C( lpeg.R'az'^1 )
local PLIST = WS * ( NAME * ( WS * ',' * WS * NAME )^0 )^-1
local FCALL = lpeg.Cc'FCALL'
* lpeg.Ct( WS * NAME * '(' * PLIST * WS * ')' )
local ALL = lpeg.Ct( FCALL^0 )
with
lpeg.match( ALL, [[
foo( bar, baz )
asdf( qwer )]] )
results in the table
{
'FCALL', { 'foo', 'bar', 'baz' },
'FCALL', { 'asdf', 'qwer' }
}
which can be interpreted as the list of expression types ('FCALL'),
followed by a data structure containing the function name and the
arguments.
For better readability and "type safety" I'd rather like it to be
{
'FCALL', { name = 'foo', args = { 'bar', 'baz' } },
'FCALL', { name = 'asdf', args = { 'qwer' } }
}
Currently, I'm achieving this by a second transformation step.
I'm pretty sure this can be directly done by some clever trick in the
LPeg expressions above.
Please drop me a hint on how to do it.
Any other suggestions are welcome, even a "This is not the way to do it,
usually you do [...]".
Regards,
Matthias