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Re: Syntax-rules generate symbol

From: Taylan Ulrich B.
Subject: Re: Syntax-rules generate symbol
Date: Tue, 10 Sep 2013 11:16:12 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (berkeley-unix)

Panicz Maciej Godek <address@hidden> writes:

> I assume that the main reason for using this is efficiency (rather
> than simplicity), because allegedly guile's continuations are rather
> inefficient.
> On one hand, it's good to know that (and would be even better
> to be able to find it out by skimming section 6.13 of the manual),
> but on the other it would be nicer if the compiler could trace the
> usages of continuations and figure out whether a given one is
> ever being re-entered, and optimize accordingly.

Delimited/composable continuations don't have the efficiency problems of
call/cc (some of which are inherent, and not related to Guile, from what
I know), and I'd urge anyone to read the following critique of call/cc
revealing other problems with it as well. :)

Guile supports "prompts" as the primitive behind higher-level delimited
continuation operators, escape continuations, exceptions, etc.  The
relevant manual section is a nice read, though it might require more
than a quick skim:  (info "(guile) Prompts")

The compiler might be able to optimize some usages of call/cc into the
more efficient use of a delimited continuation, but after reading about
call/cc and delimited continuations, it becomes a rather blurry line
(IMO) which generalizes which, and on the meanwhile I find it most nice
to use the abstraction that expresses the actual idea as directly as
possible.  And since breaking from a loop or returning from a block are
inherently escape-only actions, I think it's actually nicer to use
`let/ec' for those cases even in terms of code clarity etc.

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