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Provides an enhanced MULTIPLE-VALUE-BIND macro that adds support for lambda keywords by expanding to a MULTIPLE-VALUE-CALL when necessary. This makes catching multiple-value &rest and &key much more lightweight and convenient. A MULTIPLE-VALUE-&BIND alias is supported.
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enhanced-multiple-value-bind.asd
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README

Project's home: http://www.hexstreamsoft.com/projects/enhanced-multiple-value-bind/


enhanced-multiple-value-bind provides an enhanced MULTIPLE-VALUE-BIND
macro that adds support for lambda keywords by expanding to a
MULTIPLE-VALUE-CALL when necessary. This makes catching multiple-value
&rest and &key much more lightweight and convenient. A
MULTIPLE-VALUE-&BIND alias is supported.

Some problems with writing out MULTIPLE-VALUE-CALL with an inline
LAMBDA, especially with a big LAMBDA body and trivial form arguments
to m-v-c, compared to MULTIPLE-VALUE-BIND, are:

- "unnatural" order of evaluation (skip over LAMBDA, evaluate values
  forms, then "come back" for LAMBDA body);

- significant extra indentation for the body.

Multiple-value &rest and &key are currently not being used a lot, but
the awkwardness of using them up to now might have something to do
with this state of affairs. Their usefulness and convenience should
now be reassessed.


If enhanced-mvb:MULTIPLE-VALUE-BIND is invoked without apparent lambda
keywords (symbols beginning with "&"), then it simply expands to
cl:MULTIPLE-VALUE-BIND:

(enhanced-mvb:multiple-value-bind (a b c) (values 1 2 3)
  ...)
==
(multiple-value-bind (a b c) (values 1 2 3)
  ...)

Else, it simply expands to a MULTIPLE-VALUE-CALL with inline LAMBDA:

(enhanced-mvb:multiple-value-bind (a b &rest rest) (values 1 2 3)
  ...)
==
(multiple-value-call (lambda (a b &rest rest)
                       ...)
  (values 1 2 3))

An interesting consequence of this is that it's easy to accept an
exact number of return values (though I'm not sure why you'd want to):

(multiple-value-bind (a b c &optional) (values 1 2 3 4))
error --> "Invalid number of arguments: 4"

This follows the same principle as VALUES in FUNCTION type specifiers.
CLHS VALUES (type specifier):
http://www.lispworks.com/documentation/HyperSpec/Body/t_values.htm


To use enhanced-multiple-value-bind, either refer to the provided
MULTIPLE-VALUE-BIND directly:

;; A bit long...
(enhanced-multiple-value-bind:multiple-value-bind
      (x y &rest others)
    (values 1 2 3 4)
  (values (* x y) others))
=> 2, (3 4)

;; Much more managable package nickname.
(enhanced-mvb:multiple-value-bind (x y &rest others)
    (values 1 2 3 4)
  (values (* x y) others))
=> 2, (3 4)

Or (:shadowing-import-from #:enhanced-multiple-value-bind
#:multiple-value-bind) in your DEFPACKAGE (or with the package
nickname, again). Don't (:use)!

enhanced-multiple-value-bind also exports MULTIPLE-VALUE-&BIND, with
exactly the same functionality, so you can (:import-from
#:enhanced-multiple-value-bind #:multiple-value-&bind) in your
DEFPACKAGE instead if you want.


This library is in the Public Domain.
See the UNLICENSE file for details.
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