[r6rs-discuss] "Unspecified"

From: David Cuthbert <dacut>
Date: Thu Sep 21 22:52:41 2006

Anton van Straaten wrote:
> When you write (if b x) in a program, you haven't specified what should
> be returned if b is false. The value of the expression in that
> situation is unspecified.

This sentence is confusing. The value of the expression is specified by
the standard. A conforming implementation cannot return #f in this
situation (or null, or "", or ...).

> The perpetrator of the unspecified behavior
> is not the R6RS draft, but rather the program(mer). The R6RS draft
> simply specifies that in such situations, implementations must return a
> value which denotes that no value was specified.

Reading this makes me biased for changing the terminology. Many readers
will subconciously parse "unspecified" as "implementation-defined"; it
will take a fair amount of mental gymnastics (for me, at least) to parse
it as "the value when no value was specified."
Received on Thu Sep 21 2006 - 22:52:04 UTC