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Re: [Scheme-reports] "unspecified values"

On Thu, May 19, 2011 at 1:10 PM, Andy Wingo <wingo@x> wrote:
I do not agree with the note that permitting any number of values to be
returned from `set!' et al is incompatible.  It is not incompatible with
implementations, as it widens the scope of what they may do.....

Requiring a single unspecified value means that:

    (let ((x (if #f 'never))) <stuff that does not depend on x>)

is legal Scheme code (based on the interpretation that initializers *must* return a single value, unspecified or not).

So, allowing implementations to return multiple or zero unspecified values would actually shrink the language from what it used to be.   This is what I observe the WG tries very hard to avoid, especially if "lots of existing code" depends on the status quo.

I know nothing about the existing code that depends on this particular feature.   I would personally have preferred "any number", as it's handy for detecting buggy code.

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