[R6RS] Making -> a valid identifier

[William D Clinger]

Kent wrote:
> The simplest approach to adding symbols that start with -> would be the
> one you suggested a long time ago:
> 
>   <peculiar identifier> -> + | - | ... | -> <subsequent>*
> 
> This is "piling feature on top of feature", but anything else short of an
> "excluding <number>" solution will likely further complicate the identifier
> grammar and still feel like piling feature on top of feature.

I agree with the productions shown above.

I really don't like the non-monotonicity of treating
anything that doesn't parse as a number as an identifier.

> If we do figure out how to add identifiers that start with -> to the
> language, should we rename exact->inexact to ->inexact and inexact->exact
> to ->exact?  It's always seemed funny that exact->inexact allows inexact
> inputs and inexact->exact allows exact inputs.

That would be fine with me, except I'd want to retain the
exact->inexact and inexact->exact names for backward
compatibility.  They could be banished to the R5RS
compatibility library.

Will