Re: order of evaluation John Cowan (05 Apr 2006 16:26 UTC)
Re: order of evaluation John Cowan 05 Apr 2006 16:26 UTC
Sebastian Egner scripsit:
> Now the rationale for <unspecified order> in procedure
> application is...
> ...not really obvious to me, either. My guess:
> a) Theory people like it big time because the order of
> evaluation of argument expressions is a non-essential
> feature of the model, and would have to be introduced
> into the semantics artificially afterwards.
> b) Implementations are free to choose the internal
> representation of argument lists, and hence also the
> algorithms for evaluating these expressions.
The C language allows the same freedom to implementors, and
probably for the same reasons: on some machines it's faster
to evaluate LTR, on others RTL is better, depending on the
natural growth direction of the stack.
C has a mild advantage over Scheme in this area, in that
Scheme systems are compelled to treat a variable
number of arguments as a Scheme list, whereas C uses
magic syntax to provide access to such arguments.
(This is the only place in which a Scheme datatype is
actually exposed other than through the standard library.)
John Cowan www.ap.org www.ccil.org/~cowan firstname.lastname@example.org
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