Re: [Pyparsing] DSL using pyparsing

[Asim M. <as...@ho...>]

Thanks Paul, I think i have the idea now. I am using Imputil, so the problem i have now is that i am using imputil, so when say i am trying to compile a script, say:
 
A = Color(100, 10, 50)

I get a "NameError: name 'Color' is not defined". Any ideas?


> From: pt...@au...
> To: as...@ho...; pyp...@li...
> Subject: RE: [Pyparsing] DSL using pyparsing
> Date: Wed, 10 Jun 2009 14:17:50 -0500
> 
> Asim -
> 
> I would work on this like they dig a tunnel - from both directions.  First I
> would write out what my DSL syntax would be.  Then I would work backwards
> and write out how this would be implemented in Python.  The purpose of the
> pyparsing DSL converter is to find your DSL syntax, and then create the
> related Python code.
> 
> Let's say your application was something about RGB colors, and A and B are
> going to be colors which, when added together, result in a third color whose
> RGB values are the respective sums of the R, G, and B values of A and B.
> Let's say this is your color syntax:
> 
> A = < 100 10 50 >
> B = < 0 0 0 >
> C = A+B
> 
> The purpose of the DSL converter is to convert the "<>" syntax into a
> Python-compatible API call (probably a constructor call to a Color class).
> The "C=A+B" line probably doesn't need DSL handling, your Python Color class
> can define the __add__() function to do the proper R, G, and B summing.
> 
> So all your DSL converter in this case would need to do would be to change:
> 
> A = < 100 10 50 >
> 
> To:
> 
> A = Color(100, 10, 50)
> 
> In pyparsing this is a very simple thing:
> 
> LT,GT = map(Suppress,"<>")
> Integer = Word(nums)
> colorDef = LT + integer*3 + RT
> colorDef.setParseAction(lambda tokens : "Color(%s, %s, %s)" % tokens)
> 
> Then use colorDef.transformString() to convert the source read from the
> imported file into valid Python, and then use that to compile into the
> executable module.
> 
> Remember, you are generating a Python script from your DSL script, so you
> don't have to worry about "carrying values forward from one line to the
> next" - when your generated code gets compiled to Python bytecode, it will
> do this for you.
> 
> Don't try to re-invent Python with your DSL.  You are *much* better off
> using your DSL to *augment* the Python syntax.
> 
> Thanks for reading the article!
> 
> -- Paul
> 
> 
> > -----Original Message-----
> > From: Asim Malik [mailto:as...@ho...]
> > Sent: Wednesday, June 10, 2009 1:58 PM
> > To: pyp...@li...
> > Subject: [Pyparsing] DSL using pyparsing
> > 
> > 
> > Ok i am looking at building a DSL using pyparsing and am relatively new to
> > python . Intially I am looking at something like this:
> > 
> > A = {build some list, this calls some underlying python api and creates
> > say a class A}
> > B = {build another list, this creates another python class B }
> > C= A+B
> > 
> > Should i parse this as a single script or parse each statement? If i parse
> > each statement how can i pass variables that were defined in the previous
> > statement? As the complexity of the doamin increase, it might be the case
> > that the construction of A depends on other statements. What i am looking
> > for is the best approach.
> > 
> > Thanks
> > 
> > 
> > 
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