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From: Georg Bauhaus <sb463ba@l1-hrz.uni-duisburg.de>
Newsgroups: comp.lang.ada
Subject: Re: In-Out Parameters for functions
Date: Fri, 30 Jan 2004 23:25:37 +0000 (UTC)
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Hyman Rosen <hyrosen@mail.com> wrote:
: Georg Bauhaus wrote:
:> People coming from the substitution model of programming...
:> I'm only trying to see how this could make sense.
: 
: I'm trying to see how someone could believe that fixing an order of
: evaluation doesn't make sense. Of what use is arbitrariness to the
: semantics of the language?

I had people in mind, not just programming languages.
You might say it makes sense to adapt one's reasoning to the
requirements of a programmaing language/style etc.
For predicting properties of object code this might be necessary
in addition to checking. However, do you define or design high
level languages to just produce object code in a systematic
manner or is there more to it? Like expressiveness, dealing well
with what people (not: Scheme fans, Ada fans, APL fans)
usually do when writing programs? Languages that suggest
ways of commanding a computer to "execute an idea"?

In the substitution model you don't have to worry about
the order of evaluation, that is, you reduce complexity.
However, the world has state, and no rollback, so the 
substitution model may not work.

Consequence: In the presence of time dependence, learn to
"think from left to right" in addition to down the sequence
of instructions.
Alternative consequence: In the presence of time dependence, if you
want a specific order of elaboration, say so in the direction
of declarations and statements, but not when it comes to
"inputs" to "value creating items". (I admit that this is somewhat
artificial.)

If you say that the idea of substitution should not be a guideline
when variables can have changing values, you might want order of
evaluation to imply consistency with western wrinting direction in all
respects. I.e. I am weighting other aspects of source code constructs
less, like "a collection of inputs to a function where each
input is named" --conceptually the order of association is an addon
necessitated by that nasty time dependent statefulness of the world
in case there are globals or inputs or side effects.