[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Date: Wed, 22 Feb 89 11:52 EST
From: Stever@YUKON.SCRC.Symbolics.COM (Stephen Robbins)
Date: Wed, 22 Feb 89 09:27 EDT
>From: Jeffrey Mark Siskind <Qobi@zermatt.lcs.mit.edu>
>Jonathan Rees has a Scheme compiler for the 3600. I have never used it
>so I can't comment on its quality. Actually I would very much like
>the plain 3600 Common Lisp compiler to support tail recursion (and
>continuations as well --- though the latter would require some
>extensions to the language.) Many times I have taken to writing loops
>instead of tail recursive calls solely for performance reasons and
>would like to be able to stop that practise.
I thought the CL compiler DID support tail recursion properly?
At least, when I disassemble tail-recursive code I see a CALL-1-RETURN
which I have been (improperly?) assuming corresponded to a branch
instruction, nicht wahr?
Nope. CALL-1-RETURN leave a stack frame.
I've asked for years for some way to allow tail-recursion. DCP sent me
an excellent discussion of tail-recursion issues (which I've long since
deleted), which boiled down to two points:
I suspect there must have been more points which you've forgotten. One problem
is that there is a fair amount of state associated with a stack frame that pertains
to cleanup now that would have to be stored elsewhere if multiple invocations of
a function shared a stack frame. Two that come to mind immediately are unwind-protects
and stack-consed-presentation cleanups.
Also, how do you set the trap-on-exit flag on one (but not several) of these tail-recursively