multiple-value-constantly

Improvement to Common Lisp:

Macro multiple-value-constantly

(multiple-value-constantly form*)

multiple-value-constantly evaluates each form, gathers all the values together, and yields a constant function that takes any number of arguments and returns the gathered values. It’s the spawn of multiple-value-call and constantly.

constantly could be defined as (defun constantly (it) (multiple-value-constantly it)).

Here’s my implementation:

(defmacro multiple-value-constantly (&rest forms)         
  `(multiple-value-call                                                         
    (lambda (&rest l) (lambda (&rest any)                                       
                        (declare (ignore any))                                  
                        (values-list l)))                                       
    ,@forms))

May induce funny feeling in Lisp programmers:

(setf (symbol-function 'constantly-nothing)
      (multiple-value-constantly))

(constantly-nothing)

Of course, you have to be careful using multiple values; they can be tricky.

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