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Date: 7 Apr 92 19:05:13 GMT
From: young@purdue.edu  (Michal Young)
Subject: Re: how pure are functions?
Message-ID: <18363@ector.cs.purdue.edu>
List-Id: <comp.lang.ada>

In reply to: 

>    Are they free from internal state?
>No.

Mark Biggar says: 
> More then likely that variable is only visible in the body of the package
> that defines the function and so is invisible to the user of the function,
> but strictly the function itself has no "internal" state. 

This is true, strictly speaking, but from the viewpoint of a user,
verifier, or compiler, Ada functions do not appear to be stateless.
For instance, one cannot generally substitute 2*f(x) for f(x) + f(x).
There are good practical reasons for not insisting that every
"function" be a pure function, but it would be quite helpful if the
language provided some way to indicate that certain "functions" were
actually functions in the mathematical sense.

--Michal Young
-- 
Michal Young