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Re: [OT] Re: Question on mutability of argument lists
From: |
Andy Wingo |
Subject: |
Re: [OT] Re: Question on mutability of argument lists |
Date: |
Thu, 20 Mar 2014 22:02:02 +0100 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux) |
On Thu 20 Mar 2014 11:06, Marco Maggi <address@hidden> writes:
> Something similar can be done for return values[1]; in
> Vicare every function call site has 2 return points: one for
> single return value; the other for 0, 2, more return values.
> One return point goes on with the computation, the other
> raises an exception.
>
> [1] Ashley and Dybvig. "An Efficient Implementation of
> Multiple Return Values in Scheme". Proceedings of the 1994
> ACM Conference on Lisp and Functional Programming, 140-149,
> Orlando, June 1994.
Incidentally I think this is not such a nice approach -- multiple-value
returns kill the return-branch buffer. I suspect this is a very 1994
strategy. For example, it's common to call a function and discard its
arguments. This is trivial with a single return location. With MV you
miss the return-branch buffer and you still play jump games. The
single-value return is also very easy -- just check the
number-of-return-values register (or, if values are on the stack, check
the stack pointer) and branch to error if you didn't get the right
number. Branch prediction helps here.
Andy
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