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Date: Wed, 28 Mar 2007 09:59:59 +0200
From: "Loup Vaillant" <loup.vaillant@gmail.com>
To: caml-list@yquem.inria.fr
Subject: How must we teach lexical scope?
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X-Spam: no; 0.00; syntax:01 blog:98 lexical:01 lexical:01 closures:01 defined:02 defined:02 caml:02 functional:02 functional:02 scope:03 scope:03 programming:03 suffice:03 variable:06 

My brother is currently learning Camllight at the Toulouse 3
university, France. Five years ago, I followed the same course.

I don't understand the way were are taught lexical scope. Our
professors used "environments", where free variable would suffice.
(An environment is the set of defined values at a given time. The
environment of a value is the environment of when this value is
defined.)

-> They talk about closures, even in the case of pure functional
style, even in the absence of free variable (except the built in
constructions, such as '+').
-> They take hours and hours of boring an silly looking exercises
about environment, so we can understand how important environments
are.(we even had to learn a specific syntax to talk about them).
-> The promised power of the language is completely overlooked. Even
the crippled Pascal on my calculator looked more powerful.

Luckily, I had later a professor, who showed us the real power of
Caml. He didn't talked about environments.

So here are a few questions:
-> Is lexical scope that important when learning pure functional programming?
-> Are environments helpful (even the slightest bit) when teaching
lexical scope?
-> Where does this idea come from? I have not read a single book, as
single article nor blog talking about environments.
-> How can we teach lexical scope? Is there a simple solution, the
kind of a first year student can understand in less than an hour?

Thanks,
Loup