Execute user code in Parse() rather than Execute() #53

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2. pointlander commented on Aug 20, 2016

   

   pointlander

   on Aug 20, 2016

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   Some PEGs do support early code execution (http://piumarta.com/software/peg/),
   but I don't think this is a good idea in general because PEGs do
   backtracking. Example:
   a <- { code } 'a' / 'b'
   with early code execution 'code' would be executed even if the next
   character isn't 'a'. You might want to use:
   https://github.com/go-yaml/yaml
   You could still use my implementation of peg by handling the significance
   of white space after parsing. You could call AST() and then do a transform
   on the ast as a function of white space.

   On Sat, Aug 20, 2016 at 1:25 PM, wvxvw notifications@github.com wrote:

   I was hoping to use this parser generator to parse YAML, but to do this, I
   need to depend on indenting while matching rules. Executing user code in
   Execute() thus is too late for me.

   Is it possible, and if not, how difficult would it be to add functionality
   needed to do something that'd enable early code execution?

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3. pointlander commented on Aug 20, 2016

   

   pointlander

   on Aug 20, 2016

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   &{ ... } is a predicate
   

   peg/peg.go

   Line 1407 in 1d0268d

   case TypePredicate:

   
   is the code generated for a predicate.
   Example:
   a <- &{ false }
   is a rule that will always fail.
   If you want to put code inline with peg you could use !{ ... }

   On Sat, Aug 20, 2016 at 2:05 PM, Andrew Snodgrass pointlander@gmail.com
   wrote:

   Some PEGs do support early code execution (http://piumarta.com/software/
   peg/), but I don't think this is a good idea in general because PEGs do
   backtracking. Example:
   a <- { code } 'a' / 'b'
   with early code execution 'code' would be executed even if the next
   character isn't 'a'. You might want to use:
   https://github.com/go-yaml/yaml
   You could still use my implementation of peg by handling the significance
   of white space after parsing. You could call AST() and then do a transform
   on the ast as a function of white space.

   On Sat, Aug 20, 2016 at 1:25 PM, wvxvw notifications@github.com wrote:

   I was hoping to use this parser generator to parse YAML, but to do this,
   I need to depend on indenting while matching rules. Executing user code in
   Execute() thus is too late for me.

   Is it possible, and if not, how difficult would it be to add
   functionality needed to do something that'd enable early code execution?

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   You are receiving this because you are subscribed to this thread.
   Reply to this email directly, view it on GitHub
   #53, or mute the thread
   https://github.com/notifications/unsubscribe-auth/AAPZFBBFFoYZ7PtWaAkpNAmiWs0bPnTOks5qh1TFgaJpZM4JpJTz
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5. awalterschulze commented on Aug 21, 2016

   

   awalterschulze

   on Aug 21, 2016

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   @wvxvw I would really liked to see your completed parser.
   Since I would like to create a parser, in future, that satisfies this interface:
   http://katydid.github.io/parser/addingparsers.html
   This way I can have a yaml validator language.
7. awalterschulze commented on Aug 24, 2016

   

   awalterschulze

   on Aug 24, 2016

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   Ok I just skimmed the yaml spec. I think I will be preferring your PEG spec :) I am patient.