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From: Jean-Louis Leroy <jll@skynet.be>
Newsgroups: comp.lang.beta
Subject: Re: Is Beta a statically typed language?
Date: Tue, 12 Jan 1999 23:44:17 +0100
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In article <77b7fc$l2o$1@xinwen.cs.au.dk>, Ole Lehrmann Madsen wrote:

> BETA is not completely statically typed.

I'm not obsessed with perfect type safety anymore. After having had a very 
successful relationship with C++ as a one-man team, I've reconsidered after 
spending the last two years with colleagues who were competent and talented 
programmers without being - or willing to become - language lawyers with a law 
book that runs for 800 pages.

In the case of C++ paranoid static type checking lead to the introduction of 
flexibility features (i.e. templates) which have introduced way too much 
complexity in the language. IMHO.

I've taken a long look at Perl. I think it's one of the most productive 
alternatives for many problems, however, I want the compiler to help me in 
those situations where I add or change the type of a parameter.

IOW I'm looking for *usefully* typed languages ;-)

Back to the point; my Animal & Fruits example was of course poor design, 
because an animal that only eats bananas is *not* an animal that eat all 
fruits.

Unfortunately the current Beta collections suffer from the same problem:

(#
   Person: (#  #);
   people: @Set (# element:: Person #);
   backdoor: ^Set
do
   &Person[]->people.insert;
   people[]->backdoor[]; (* no warning *)
   &integerObject[]->backdoor.insert (* trouble *)
#)

The problem here is that there exists an automatic, silent conversion from a 
Set of Persons to a Set of Objects. Couldn't this be avoided by introducing 
some form of 'partially private' inheritance? For example, by specifying that a 
subpattern that refines a virtual type that is used in an enter-list inherits 
the implementation of the superpattern without being a subtype of it?

Aw, one step toward Beta++ :(

> We have discussed these issues in several papers

I have tried to find them in electronical form, without success so far. How can 
I obtain them?

Jean-Louis Leroy
http://ourworld.compuserve.com/homepages/jl_leroy/