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From: Brian Rogoff <bpr@shell5.ba.best.com>
Subject: Re: Announce: OpenToken 2.0 released
Date: 2000/02/01
Message-ID: <Pine.BSF.4.21.0002011403400.9470-100000@shell5.ba.best.com>#1/1
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Date: 2000-02-01T00:00:00+00:00
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On 1 Feb 2000, Hyman Rosen wrote:

> Brian Rogoff <bpr@shell5.ba.best.com> writes:
> > (1) Exceptions: raise a Not_Found when input is exhausted. Some people 
> >     hate this because "Exceptions are only for error handling, not
> >     control flow!". OCaml (and SML too I think) use exceptions for this, 
> >     and Ada sometimes does (try reading a file stream without using
> >     File_Type...)
> 
> I don't like this much.
> Exceptions are for error handling, not control flow :-)

De gustibus non est disputandum. I've gotten used to this technique, and
lived to talk about it.

> > (2) Provide a query on the sequence, like in Java, so you have code like 
> >     while Has_More_Elements(Seq) loop 
> >         Char := Get_Next_Element(Seq);
> >         ...
> >     end loop;
> >     I find this very readable.
> 
> Unfortunately, when it comes to input, it is impossible on most systems
> to divorce a test for end of input from the attempt to read the input.

Exactly true, and as you say unfortunate too. 

> > (3) Provide an option type like in (OCa|S)ML which wraps returned elements 
> >     and forces the reader to unwrap them, like this
> 
> This is the integer/character thing dressed up in high-falutin' clothes.

True, though the high falutin thing is more general and much less prone to 
error since it expresses the intent clearly. Its also easily expressible
in C++ (your favorite language?) and other languages which have some form
of parametric polymorphism and variant types. I suppose you can do it in
Eiffel too but faking variants (tagged unions) with classes is an extra
level of ugliness IMO. 

I prefer using exceptions here, but I bet most Ada programmers agree with 
you and would like a procedure with a two out params.

-- Brian