Re: Using '-1' in a method named '*'

[Andy Wingo]

On Mon 27 Feb 2017 20:21, Andy Wingo <address@hidden> writes:

> Hi,
>
> On Mon 27 Feb 2017 11:06, Alejandro Sanchez <address@hidden> writes:
>
>> (define v (make <vector3> #:x 1))
>>
>> (* -1 v)  ; Does not work
>> (* -2 v)  ; Works fine
>
> I believe that Guile is doing strength reduction, transforming (* -1 v)
> to (- 0 v).

I spoke too soon.  Guile 2.1.x does indeed do this at compile-time, but
only if "v" is an instance of a built-in number type.  Guile 2.0.x
doesn't do this strength reduction at all at compile-time.

It turns out there is an easier way to reproduce this bug without GOOPS:

   (* -1 "")

scm_product was handling this case specially because of weird
implementation reasons (making sure that negating the most negative
fixnum was a bignum; see b5c40589).

In summary I think Guile's strength reduction is fine as it relies on
type inference to prove when it is safe.  This is "just" a bug, albeit
an annoying one that we need to fix!

Andy