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Re: no constants please tb@xxxxxx 28 Dec 2003 09:45 UTC

Michael Sperber <> writes:

> >>>>> "Tom" == Tom Lord <> writes:
> Tom> Either way, these "constants" wind up having exactly the same style of
> Tom> interface as SCHEME_ENTER_* rather than a special case interface that
> Tom> refers to their traditional implementation using immediate
> Tom> representations.
> OK, point taken.  But why is that a reason to have SCHEME_FALSE()
> instead of SCHEME_FALSE?  (Alternatively: why does Scheme allow EQ? to
> work on booleans, and use #f instead of (false)?)

I have no objection to exactly which C function should be used to
check for falsity.  My insistence is that it should always look like a
function, and not like a C constant; nor should C's == be used to
compare Scheme objects.

There may well be more than one C object which all collectively
represent the same Scheme object, and which are eq? to each other, but
not == to each other.

So the SRFI better not constrain an implementation.

It cannot promise to a C programmer that SCHEME_FALSE is a constant,
hence it should be SCHEME_FALSE() which returns a false value.

Then it cannot promise that the following tests whether foo is #f:
  foo == SCHEME_FALSE()

so it must have something like


This is about making sure that the C syntax does not forclose certain
sensible Scheme implementation strategies.