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RE: Undefined evaluation order
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Date: 2000-10-16 (17:47)
From: Brian Rogoff <bpr@b...>
Subject: Re: Undefined evaluation order
On Mon, 16 Oct 2000, Christophe Raffalli wrote:
> It seems to me that a program making use of evaluation order in function
> or constructor application is wrong !

Why? It seems right to me, when you're reading in a file of records or
building an AST from a file, or whatever, to depend on the evaluation
order when building the data structure. I didn't get surprised, because I 
know OCaml is right-to-left, but I still find all of that let binding code 
redundant, especially when the records get long. There is nothing "wrong" 
about it that I can see, except that some people don't like it in concept.
Interestingly, some people really did like it in concept and some of them 
were teachers who've witnessed beginners stumble over this very issue.

> It seems easy to me to add some marking in the type system to detect 
> expression with side effects ... 

I thought about this too. Something like Clean's uniqueness types? Maybe
in OCaml 4 :)

> then one could have a warning (or even
> an error :-) when some code depends on evaluation order and then, in
> this case only, force left to right evaluation order.

What does this mean? That you would have the programmer manually insert 
lets to force the order, or that the compiler does so automatically? 

> I am sure I would find some bugs in my programs with such a warning :-)

I think the random evaluation order that someone proposed as a test/debugging 
tool might be easier than a modification of the type system.

-- Brian