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From: wojtek@power.com.pl (Wojtek Narczynski)
Newsgroups: comp.lang.ada
Subject: Re: What evil would happen?
Date: 13 Jul 2003 15:36:00 -0700
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"Chad R. Meiners" <crmeiners@hotmail.com> wrote in message news:<bes4uv$1o29$1@msunews.cl.msu.edu>...

> > "Functions" with side effects can only inject their side effect into
> > where they have been hardcoded to.
> This is wrong.  Function have the capability to randomly introduce side
> effects just like any other section of code.

Have you read the whole thread?

> In my experience, functions are more useful
> when they are pure.  Sure there are times when a function cannot be pure,
> but sub-routine with a side-effect should be made a procedure in most cases.

I agree that functions should be pure. But procedures cannot return an
unconstrained value. Again, this is what this thread is about.

> In mathematics, functions only return single elements, which may be a
> composite of some sort.

Well, in the mathematical definition there is no "call" so there may
not be a "return". Instead there are two sets...

> I suggest that if you want return composites from
> functions you should return a record type.
> 
> type Composite(StringSize : Natural) is record
>      User_Name : String(1..StringSize);
>      Result    : Boolean;
> end record;
> 
> function Parse_User_Name(Item : String) return Composite;
> 
> However, the following might also be a suitable procedure for the task

Yes, this works, but causes code explosion, and memory copying (when
gathering all the parsed pieces together). This is what you can neatly
do in SML with tagged union types, by the way :-)
 
> procedure Parse_UserName (Item : String;
>                                               UserName : out String;
>                                               NameSize : out Natural) ;

This works fine for shor strings, but for longer there will be
unnecessary storage allocation.

Regards,
Wojtek