Path: utzoo!attcan!uunet!snorkelwacker!apple!autodesk!peb
From: peb@Autodesk.COM (Paul Baclaski)
Newsgroups: comp.lang.scheme
Subject: Re: Scheme as an extension language and call/cc
Summary: a more efficient implementation for call/cc
Message-ID: <118@autodesk.UUCP>
Date: 17 Sep 90 21:19:54 GMT
References: <PK.90Aug21114528@kaarne.tut.fi> <409@data.UUCP> <AXI5NUG@xds13.ferranti.com>
Distribution: comp
Organization: Autodesk Inc., Sausalito, CA
Lines: 25

In article <AXI5NUG@xds13.ferranti.com>, peter@ficc.ferranti.com (Peter da Silva) writes:
> 	 ... Specifically, in every one of
> 	 the dozen Scheme implementations that I have tested CALL/CC
> 	 allocates so much memory that most of the run time is spent
> 	 in the garbage collector."
> 		-- Paul Haahr,
> 		   "Montage: Breaking windows into small pieces",
> 		   USENIX conferance proceedings, Jun 11-15, 1990.
> 
> This is exactly the environment an extension language is needed for. For
> what you need CALL/CC for in such a program CALL/CC is not fast enough.
> Thus I would consider CALL/CC to be a luxury in this environment.

See "Representing Control in the Presence of First-Class Continuations"
by R. Hieb, R. K. Dybvig, Carl Bruggeman in ACM SIGPLAN '90 Conference
Proceedings, pp. 66-77.

They present an excellent analysis of the tradeoffs involved in 
implementing call/cc and describe a new method for implementing it
that does not have unbounded copying or a high procedure invocation
cost.  Apparently, Chez Scheme implements their new method.


Paul E. Baclaski
peb@autodesk.com