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Re: Folding comprehensions




Two things are different from SRFIs 1, 13, and 43:

1. FOLD-EC is a macro and the reduction is specified by an _expression_
with free variables. This means there is no syntactic gain by having
another variant.

2. In general, the number of elements produced in the sequence of
bindings enumerated by an eager comprehension not known in advance.
   This implies that the only possible implementation of FOLD-RIGHT-EC
first enumerates the entire sequence of bindings and then starts the
reduction process. In my opinion this has no place in a library reduced
to the most important functionality.

Sebastian.

----
Dr. Sebastian Egner
Senior Scientist
Philips Research Laboratories
Prof. Holstlaan 4 (postbox WY63, kamer WY 6-55)
5656 AA Eindhoven
The Netherlands
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email: sebastian.egner@xxxxxxxxxxx








srfi-42-request@xxxxxxxxxxxxxxxxx

18-06-2003 20:40

       
        To:        srfi-42@xxxxxxxxxxxxxxxxx
        cc:        (bcc: Sebastian Egner/EHV/RESEARCH/PHILIPS)
        Subject:        Folding comprehensions

        Classification:        




SRFIs 1, 13, and 43 all provide FOLD-RIGHT operations; I am curious why
SRFI 42
does not provide a FOLD-RIGHT-EC.