Re: Can LPeg do basic arithmetic?

[Sean Conner <sean@...>]

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.

> 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.  

  There exists a PEG generator for C [1], but none of the examples would
work in LPeg, mainly because of the embedded C 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 ... )

[1]	http://piumarta.com/software/peg/