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Re: [Gcl-devel] More on proclaim error

From: Paul F. Dietz
Subject: Re: [Gcl-devel] More on proclaim error
Date: Thu, 18 Dec 2003 18:51:09 -0600
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.4) Gecko/20030624

Camm Maguire wrote:
Greetings!  The issue regards type specifiers of the form

(satisfies foop)

where foop is a user defined predicate.  I'm assuming typep and
subtypep can always return nil for such types?  I'm wondering in
particular if any class hierarchy or other known structure could allow
a non-nil return in certain circumstances.

SUBTYPEP is allowed to return NIL, NIL, but TYPEP has to do the
right thing.  For example:

  (typep x '(satisfies foop)) ==> (funcall (symbol-function foop) x)

Note the page for TYPEP:

  A type-specifier of the form (satisfies fn) is handled by applying
  the function fn to object.


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