[racket] procedure contract for "at least N arguments, possibly more"

From: Neil Van Dyke (neil at neilvandyke.org)
Date: Sat Jun 9 12:06:54 EDT 2012

Matthias Felleisen wrote at 06/09/2012 11:24 AM:
> Neil, do you mean something like this:

Robby answered my question in a subsequent message: the core contract 
combinators don't support saying arity "two arguments, possibly more, 
but not necessarily arbitrarily more".

Regarding what I'm doing with my code...  I didn't mean all the values 
from a history from multiple applications of P1, but all the values from 
a multiple-value-return of a single application of P1.  (See example 
below.)  And I preferred to do it without "set!".  And I'd prefer to 
make each of the multiple-value-return values from P1 a separate 
argument to P2.  My code works close enough to how I want it to

The example below shows how I want the values passed from P1 to P2.  
(Note: the "display" forms represent nested contexts, though they don't 
show it, such as for handling unwinds and exceptions, so what they 
represent is not just interleaved expressions.)

#lang racket/base

(define (f p1 p2)
   (display "do-thing-1-here\n")
   (let ((multiple-value-result-of-p1 (call-with-values (lambda ()
                                                          (p1 'a))
     (display "do-thing-2-here\n")
     (begin0 (apply p2 'b 'c multiple-value-result-of-p1)
       (display "do-thing-3-here\n"))))

(f (lambda args (printf "~S\n" `(p1 , at args)) (values 'd 'e 'f))
    (lambda args (printf "~S\n" `(p2 , at args))))


(p1 a)
(p2 b c d e f)

Neil V.

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