Re: [Pyparsing] Order problem in binary operation withoperationPrecedence()

[Ralph C. <ra...@in...>]

hi Gustavo,

> > 2.
> >     relationals = eq ^ ne ^ lt ^ gt ^ le ^ ge
> >
> > '^' can be relatively expensive for pyparsing if there are many
> > alternatives, since all alternatives will be checked.  This version
> > is equivalent:
> >
> >     relationals = eq | ne | le | ge | lt | gt
> 
> Thanks for the hint. I used pipes initially but for some reason some
> tests didn't pass... I've just restored the pipes and the all the
> tests pass now, though :-S
> 
> > (I *did* have to be careful about the order, having to check for
> > "<=" before "<", and ">=" before ">".)
> 
> Could you please elaborate on that? Is it for performance reasons?

`^' causes all alternatives to be tested, `|' stops at the first one
that succeeds.  If using `|', unless you test for `<=' before `<' then
`<=' would never be seen because it would always look like a `<'.  With
`^', I assume the longest one that succeeds is used so both `<' and `<='
match but the latter is used.

Cheers,


Ralph.