Path: utzoo!attcan!uunet!husc6!uwvax!dogie!uwmcsd1!csd4.milw.wisc.edu!markh
From: markh@csd4.milw.wisc.edu (Mark William Hopkins)
Newsgroups: comp.lang.lisp
Subject: Re: Functions vs. Procedures in Lisp
Message-ID: <6035@uwmcsd1.UUCP>
Date: 18 Jun 88 17:49:08 GMT
References: <34296@linus.UUCP> <1350017@otter.hple.hp.com> <6024@uwmcsd1.UUCP> <51742@ti-csl.CSNET>
Sender: daemon@uwmcsd1.UUCP
Reply-To: markh@csd4.milw.wisc.edu (Mark William Hopkins)
Organization: University of Wisconsin-Milwaukee
Lines: 31

In article <51742@ti-csl.CSNET> gateley@mips.UUCP (John Gateley) writes:
>In article <6024@uwmcsd1.UUCP> markh@csd4.milw.wisc.edu (Mark William Hopkins) writes:
>>[Examples of side-effecting mathematics deleted]
>>Conclusion: Mathematical functions and programming language functions are MUCH
>>more closely related than anybody has realised up to now.
>
>I dont follow this, but if what you are saying is true, you should be able
>to write a mathematical function with side effects. Show me how to do this.
>I would like to see, for example, two functions f and g where g always returns
>the last argument passed to f.
>
>John Gateley

This is a tall order, but here it goes:

   Given a function f, let f' be the corresponding function defined on finite 
sequences:

	     f'({x1, x2, ... , xn}) = {f(x1), f(x2), ... , f(xn)}

Let F be an ordered pair (f', g) with f defined as above and g defined for 
sequences as follows:

	                g({x1, x2, ... , xn}) = xn

(Here's where the mathematical correlates of side-effects come in)

"For brevity we will suppress the prime on f' unless confusion otherwise
dictates, and we will refer to g as the 'last-argument' function of f."

... or something like that.