Re: LPEG: P(fct) seems not to consume input

[Sean Conner <sean@...>]

It was thus said that the Great Dirk Laurie once stated:
> Op Wo., 31 Okt. 2018 om 21:49 het Sean Conner <sean@conman.org> geskryf:
> >
> > It was thus said that the Great Dirk Laurie once stated:
> > > I define a function to be used with LPEG that simply returns the first
> > > character. It _cannot_ match the empty string:
> > >
> > > function fct(str)
> > >   if #str==0 then return false
> > >   else return 2,str:sub(1,1)
> > >   end
> > > end
> 
> > So the function should be:
> >
> >         function fct(subject,position,capture)
> >           if #subject == 0 then
> >             return false
> >           else
> >             return position,subject:sub(position-1,position-1)
> >           end
> >         end
> 
> Aha! I don't get *str+pos, I get *str,pos.
> 
> Let me try that in my notation:
> 
> function fct(str,pos)
>   if #str<pos then return false
>   else return pos+1, str:sub(pos,pos)
>   end
> end

  function fct(str,pos)
    if #str < pos then
      return false
    else
      return pos + 1 , str:sub(pos,pos)
    end
  end

  There, fixed that for you 8-P

> patt=lpeg.P(fct)
> (patt^-4):match"abc"  --> a b c [as expected, no fourth value]
> 
> But:
> (patt^0):match"abc" --> stdin:1: loop body may accept empty string
> 
> I don't understand why I get that.

  I don't either.  When I get that error, I start making changes to the code
until the error goes away and the code does what I want.  You could try:

	(patt^1):match"abc" + lpeg.Cc(false)

  -spc