Re: [Pyparsing] Combine problem

[spir <den...@fr...>]

Le Thu, 11 Jun 2009 12:00:32 +0900,
Sebastian Schoellhammer <ssc...@gm...> s'exprima ainsi:

> Hello there!
> 
> This is my first post to this list - first of all thanks for this awesome
> module, I could not live without it these days!
> 
> 
> My goal is to parse the following structure:
> s = """
> struct VS_OUTPUT {
>     float4 pos        : SV_Position;
>     float2 UV    : TEXCOORD0;
>     float3 vVec    : TEXCOORD1;
>     float3 lVec    : TEXCOORD2;
>     float3 nor     : TEXCOORD3;
>     float4 col     : TEXCOORD4;
>     float3 tan     : TEXCOORD5;
>     float4 lpos     : TEXCOORD6;
>     float depth     : TEXCOORD7;
>     float2 dof     : TEXCOORD8;
>     float2 VelocityUV      : TEXCOORD9;
> };"""
> 
> entryString = "float3 tan     : TEXCOORD5;"
> 
> def readStruct(s):
>     header = Literal("struct VS_OUTPUT")+"{"
> 
>     regs = Combine("TEXCOORD"+Word(nums)) | "SV_Position"
>     vType = Combine("float"+Optional(Word(nums)))
>     entry = vType+Word(alphanums)+":"+regs+";"
>     struct = header + OneOrMore(entry) + "};"
> 
>     print entry.parseString(entryString)
> 
> This is working as is - but when i change
> 
> entry = vType+Word(alphanums)+":"+regs+";"  to entry =
> Combine(vType+Word(alphanums)+":"+regs+";")
> 
> to make this into a single string, I get a parse Exception - it's not a big
> problem but I just don't understand why it doesn't work in this case :)
> Somehow I can't see the difference to where I use Combine in the lines
> above, where it seems just fine.

You should always post error messages to get help people help you. In this case:
  [.............]
  File "/usr/lib/python2.5/site-packages/pyparsing-1.5.1-py2.5.egg/pyparsing.py", line 1657, in parseImpl
    raise exc
pyparsing.ParseException: Expected W:(abcd...) (at char 6), (line:1, col:7)

In other words: pyparsing steps on the space, expecting the second part of the pattern.

If I remember well, Combine() invalidates the default "separator-skipping" mode of pyparsing (someone confirms?). Which is rather sensible, for otherwise it would join together bit that are separated in the source, which is probably not what we want in most cases.

If you wish this anyway, just join the result manually:
	result = entry.parseString(entryString)
 	print "".join(result)
or rather set a post-parse action on entry:
	entry.setParseAction(lambda node: ''.join(node))
==>
['float3tan:TEXCOORD5;']

Is this really what you expect?

Denis
------
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