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update of SRFI-42 "Eager Comprehensions"

This page is part of the web mail archives of SRFI 42 from before July 7th, 2015. The new archives for SRFI 42 contain all messages, not just those from before July 7th, 2015.

Dear SRFI-42 discussion list,

There will soon be an update of SRFI-42 "Eager Comprehensions"
available on schemers.org.

The changes I made are minimal:

1. Two ECs got renamed to align with SRFI-1:

        forall?-ec         ->         every?-ec
        exists?-ec         ->         any?-ec

This was suggested by Sven Hartrumpf. I think he is right.

2. There is one additional comprehension:

        (vector-of-length-ec <k> <qualifiers>* <_expression_>)

behaves like vector-ec, but the length of the resulting vector is
known in advance and is specified as the argument <k>.

The new comprehension allows a more efficient implementation
reducing the pressure on the garbage collector. Some quick timing
in Scheme-48 on a Pentium 4 Linux system indicates a speedup by
a factor of about 1.5.This is not overwhelming but worth the effort.
(Bear in mind that the speedup will vary greatly.)

 The new comprehension was triggered by the discussion around
SRFI-43 "Vector Library" (Taylor Campbell). Several people have
expressed their concern there that making vectors on an element-
by-element basis is inefficient.



Dr. Sebastian Egner
Senior Scientist
Philips Research Laboratories
Prof. Holstlaan 4 (postbox WY63, kamer WY 6-55)
5656 AA Eindhoven
The Netherlands
tel:       +31 40 27-42069  *** new telephone number
fax:      +31 40 27-42566  *** new fax number
email: sebastian.egner@xxxxxxxxxxx