[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: #f = #none ?

> Date: Wed, 18 Nov 1992 10:57:42 -0500
> To: info-dylan@cambridge.apple.com
> Subject: #f = #none ?
> From: Stavros Macrakis <macrakis@osf.org>
> Sender: macrakis@osf.org
> Imagine a function which takes an optional argument which is to be
> True, False, or Dont-care.  Presumably if the argument is omitted, the
> value should be Dont-care.  How will we encode these values?  We can't
> use #f for False, because it also means that the argument isn't there.
> We could use #t for true, but we'll have to be careful, because all
> boolean functions in Dylan allow any non-#f value to represent
> True....
> So perhaps we'll need to define a new type which takes values
> (singletons) True, False, and #f...  Seems silly, and error-prone.

This reminds me of a problem with CL. If Dylan doesn't address it, it 
should. For an argument in a function call, I would like to explicitly 
say  "use-the-default-value".