Wanted: warning option for usages of unary minus

[Dinko Tenev]

This last piece of conversation was *so* reminiscent of a paper[1] I once
read,  I was almost convinced it was late by 11 days...until I checked :)


Cheers,

    Dinko


[1] http://www.research.att.com/~bs/whitespace98.pdf


On 4/12/07, Simon Marlow <simonmarhaskell at gmail.com> wrote:
>
> Isaac Dupree wrote:
> > -----BEGIN PGP SIGNED MESSAGE-----
> > Hash: SHA1
> >
> > Isaac Dupree wrote:
> >> Simon Marlow wrote:
> >>>> I definitely think that -1# should be parsed as a single lexeme.
> >>>> Presumably it was easier at the time to do it the way it is, I don't
> >>>> remember exactly.
> >>>>
> >>>> I'd support a warning for use of prefix negation, or alternatively
> you
> >>>> could implement the Haskell' proposal to remove prefix negation
> >>>> completely - treat the unary minus as part of a numeric literal in
> the
> >>>> lexer only.  This would have to be optional for now, so that we can
> >>>> continue to support Haskell 98 of course.
> >>>>
> >>>> Cheers,
> >>>>     Simon
> >> Yes, I've been thinking about how to implement both - details will come
> >> later when I have more time.  I think I have a reasonably working idea
> >> of how to divide up the cases for warnings for ambiguous-looking use of
> >> both infix and prefix minus, as well as actual syntax changes...
> >
> > not considering warnings, just syntax:  123abc is two valid Haskell
> > tokens. for example:
> > \begin{code}
> > main = (\n c -> print (n,c)) 123Abc
> > data Abc = Abc deriving Show
> > \end{code}
> > prints (123,Abc).
> > So does this suggest that under a negation-is-part-of-numeric-token
> > regime, 123-456 should be two tokens (a positive number then a negative
> > number, here), as is signum-456 ...
>
> Yes, absolutely.
>
> > Presently, GHC doesn't even warn about the first thing (123abc) ^_^
>
> and remember that while '123e 4' is 3 tokens, '123e4' is only 1.
>
> Cheers,
>         Simon
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-- 

Cheers,
    Dinko
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