[Top][All Lists]

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

Re: A value for "nothing"

From: John Cowan
Subject: Re: A value for "nothing"
Date: Tue, 28 Aug 2018 11:19:06 -0400

On Tue, Aug 28, 2018 at 3:01 AM Mark H Weaver <address@hidden> wrote:

> In RnRS, (define a (if #f #f)) is allowed and guaranteed to assign
> *some* object to 'a' without signalling an error.

Actually, the phrase used is "the result is unspecified", which
is not defined in any RnRS.  Racket produces a syntax error in this
at least in its default language.

> However, it's not
> specified what object will be assigned.  It could be 2 or (foo bar) or
> "the cow jumps over the moon".

In practice, it is #t, #f, (), or a unique unspecified object across all the
Schemes I have tested, most often the last.

John Cowan        address@hidden
LEAR: Dost thou call me fool, boy?
FOOL: All thy other titles thou hast given away:
That thou wast born with.

reply via email to

[Prev in Thread] Current Thread [Next in Thread]