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Undefined evaluation order
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Date: 2000-10-10 (10:26)
From: Brian Rogoff <bpr@b...>
Subject: Re: Undefined evaluation order
On 8 Oct 2000, David [iso-8859-1] Mentré wrote:
> Brian Rogoff <> writes:
> >     It is well known that OCaml has undefined evaluation orders and that
> > it uses right-to-left ordering. What is the rationale for that decision? 
> It is linked to the way the bytecode is designed to optimize functions
> evaluation. You'll find a detailed (and more accurate) explanation in
> the following paper :
> RT-0117 The ZINC experiment : an economical implementation of the ML
> language - Xavier Leroy

Thanks David, that's exactly the kind of explanation I was looking for. 

Interestingly, I had a discussion with my manager about this and we had
slightly different views. I argued that evaluation order should be
specified and that it should be left-to-right, which I hope everyone
agrees is the most natural order. He argued that evaluation order should 
be defined so that you can analyze programs, but that the order was
irrelevant; he'd be happy with right-to-left if it were specified. For
OCaml it appears that the perspective adopted is that the programmer must
make the temporal dependencies explicit. The reason is for (bytecode) compiler 
optimizations, but it is mentioned that this usually leads to clearer programs. 
I'm sure the bytecode compiler argument is valid, but not the code clarity one, 
since it sounds similar to an argument that having uninitialized variables is 
clearer since it forces you to make values explicit, and I don't believe that.

-- Brian