Re: typechecking

[Dirk Herrmann <dirk@dirk-herrmanns-seiten.de>]

Han-Wen Nienhuys wrote:

>  mvo@zagadka.de writes:
>
> > When I say "type checking" what really mean is that the compiler
> > checks whether the user only uses SCM values in the way we want it
> > to, like, no direct arithmetic, no direct use in conditional tests,
> > only
>
>  What's the rationale for not allowing direct use in conditional
>  tests?

Code like the following:

void f (SCM obj)
{
  if (obj) {
    /* do something */
  }
}

is almost always wrong, since what the user typically wants to check is, 
whether obj is SCM_BOOL_F or not:

void f (SCM obj)
{
  if (!SCM_FALSEP (obj)) {
    /* do something */
  }
}

The first version, however, will compile if SCM is defined to be some 
pointer type.

Best regards,
Dirk Herrmann




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