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Re: typechecking

From: Marius Vollmer
Subject: Re: typechecking
Date: Mon, 17 May 2004 20:31:24 +0200
User-agent: Gnus/5.1002 (Gnus v5.10.2) Emacs/21.3 (gnu/linux)

Han-Wen Nienhuys <address@hidden> writes:

> that doesn't really answer my question. It seems to me that
>   if (obj == gh_symbol2scm("bla"))
>     ...
> is safe.

It does currently work, and will likely continue to work for a very
long time.  (Even with the strange nil/#f/() tryptich planned for
getting Elisp into Guile.)  However, for a proper abstract data type
like SCM, it would be cleaner to use SCM_EQ_P.  Setting
DEBUG_TYPE_STRICTNESS to 2 will not allow direct comparisons.

> Do I understand correctly that disallowing this is a side
> effect of trying to disallow
>   if (obj)
>     ...

No, I don't think so.  The two cases seem very different to me.  "if
(obj)" will never be correct since the SCM encoding that is considered
false by C will never occur, and more importantly, SCM_BOOL_F is not
false when seen directy by C.

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