Re: Can LPeg do basic arithmetic?

["Soni L." <fakedme@...>]

On 05/07/16 09:37 PM, Sean Conner wrote:
> It was thus said that the Great Soni L. once stated:
> > On 05/07/16 06:34 PM, Sean Conner wrote:
> > > It was thus said that the Great Soni L. once stated:
> > > > Too bad it's not pure LPeg, instead deferring to a Lua function for it.
> > >    What?  Is not lpeg.Cf() LPeg, just because it accepts a Lua function as
> > >    a parameter?  So,
> > >
> > > 	lpeg.R"09" / { ['o'] = 0 , ['1'] = 1 , ['2'] = 2 ... }
> > >
> > > is fine, but not?
> > >
> > > 	lpeg.R"09" / tonumber
> > >
> > >    If LPeg allows it, it's LPeg.
> > >
> > >    But okay, fine!  If you restrict the domain to single digits, then:
> > >
> > > 	  lpeg.P"0+0" * lpeg.Cc(0)
> > > 	+ lpeg.P"0+1" * lpeg.Cc(1)
> > > 	+ lpeg.P"0+2" * lpeg.Cc(2)
> > > 	+ lpeg.P"0+3" * lpeg.Cc(3)
> > > 	... and so on.  Go crazy with this.
> > The goal is to never run Lua code for it. Perl regex can run Perl code,
> > but the linked math-with-regex thingy doesn't use that and that's the
> > whole point. If someone ports LPeg to a different programming language,
> > a LPeg that calls Lua code will stop working.
>    That was never specified as a limititation in your initial post.
No, but it is mentioned in the linked stackoverflow question. You should 
read the full context before replying.
> > Also, if this was a codegolf or programming puzzle and you weren't
> > allowed to use the language's built-in addition subtraction etc, you
> > could do it with regex instead.
>    If this was a codegolf or programming puzzle and you weren't allowed to
> use the languages's built-in addition subtraction etc, you wouldn't be
> *ABLE* to do this using LPeg.  Period.  End of story.  That '*' in the above
> example?  That's Lua multiplication operator.
You're mistaking "operation" and "operator". In other languages, "+" is 
often overloaded for concatenation as well as addition, and in such 
challenges you're (usually) still allowed to use "+" for concatenation. 
Also LPeg has a 're' module.
>    There exists a PEG generator for C [1], but none of the examples would
> work in LPeg, mainly because of the embedded C code.
Yes, that's why you remove any sort of embedded <insert language here> code.
>    LPeg (and PEGs in general) are not regular expressions, although they can
> be used where one would use a regex (the reverse is not true).
>
>    -spc (You couldn't even port it to C++ because the ^ and ~ operators
> 	differ between Lua and C++ and thus the precedence rules would be
> 	out of wack ... )
You don't have to use operator overloading to use PEGs.
> [1]	http://piumarta.com/software/peg/

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