wrong argument type Class (expected Module) (TypeError)

[amir teshome]

I was trying to parse mathematical expression below is my treetop rules, 

rule expr 

    (term / (expr '+' term) )      <XBody>

end 

rule term     

   (factor / (term '*' factor))    <XBody>

end

rule factor

  (numd / groupd)    <XBody>

end

rule groupd

 '(' expr ')'    <XBody>

end

rule numd

 [1-9] [0-9]*  <XBody>

end

when I try to parse 2+3 i'm  getting this error 

(eval):158:in `extend': wrong argument type Class (expected Module) (TypeError)

from (eval):158:in `_nt_factor'

from (eval):97:in `_nt_term'

from (eval):30:in `_nt_expr'

from /var/lib/gems/1.9.1/gems/treetop-1.5.3/lib/treetop/runtime/compiled_parser.rb:18:in `parse'

Can any one help me out on this (I'm somehow new for treetop) thank you in advance.    

[Paul Madden]

Hi Amir,

Try this:

grammar G

  rule expr 

    term '+' expr <X> / term "" <X>

  end 

  rule term     

    factor '*' term <X> / factor "" <X>

  end

  rule factor

    numd "" <X> / groupd "" <X>

  end

  rule groupd

    '(' expr ')' <X>

  end

  rule numd

    [1-9] [0-9]* <X>

  end

end

The problem you asked about was due to the fact that Treetop only lets you associate compound rules (not single-terminal rules) with classes. But you can add an empty string terminal to a rule to make it compound, and it will not affect the parse.

Also, in rules 'expr' and 'factor': You want to try to match the longer rule first -- otherwise the short one will always match because it is a prefix of the longer rule. Also, PEGs do not support left recursion, so you want e.g. "term '+' expr" rather than "expr '+' term".

paul

[Clifford Heath]

Amir,

On 27 Jun 2014, at 1:12 am, Paul Madden <pma...@gmail.com> wrote:
> The problem you asked about was due to the fact that Treetop only lets you associate compound rules (not single-terminal rules) with classes.

Not quite. You can only associate new nodes with classes.
When an alternate in a rule calls only one other rule, no new
sequence-node is created (that would have only one element).
Instead, the same node is returned, so you cannot use a class.

> But you can add an empty string terminal to a rule to make it compound, and it will not affect the parse.

This forces a sequence node. It’s better to rewrite your class
as a module and use that instead.

Clifford Heath.

[amir teshome]

Hi Paul,

Sorry for late respond I have been some how busy, and thank you very much for your explanation, I have done what you suggested and it works now I'm trying to write other ruby class to execute the parsed result, 

I hope if I got some problem you will help me thank you       

[amir teshome]

thank you also Calliford, 

But I have seen the suggestion to change the class into module then I tried to change but it was some how messy since I have other previous code which is related to other parser, which was contained in one module with a lots of classes. So I have to change those all classes to module       

On Thursday, June 26, 2014 3:29:06 PM UTC+2, amir teshome wrote: