Re: optimizing defconst

[Stefan Monnier]

> (defconst viper-xemacs-p (featurep 'xemacs))

> (defun foo()
>   (if viper-xemacs-p (error "Hmmmm")))

> Shouldn't `foo' be optimized to just do nothing? 

Can't do it: some code might do (setq viper-xemacs-p t) before calling
`foo'.  Such code might be flagged by the byte-compiler with a warning "setq
on a constant", but it's only a warning and it's not always caught.

We could change `defconst' so that it really defines constants (on which
`setq' fails) and then such an optimization might be acceptable, but this is
a non-trivial change.


        Stefan