Implementation of reduce-right in SRFI 1
TAKIZAWA Yozo
(28 Dec 2021 08:49 UTC)
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Re: Implementation of reduce-right in SRFI 1
Arthur A. Gleckler
(08 Jan 2022 16:47 UTC)
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Re: Implementation of reduce-right in SRFI 1 Alex Shinn (09 Jan 2022 23:20 UTC)
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Re: Implementation of reduce-right in SRFI 1
John Cowan
(10 Jan 2022 04:13 UTC)
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Re: Implementation of reduce-right in SRFI 1
Alex Shinn
(10 Jan 2022 04:42 UTC)
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Re: Implementation of reduce-right in SRFI 1
Marc Nieper-Wißkirchen
(10 Jan 2022 12:02 UTC)
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Re: Implementation of reduce-right in SRFI 1
Arthur A. Gleckler
(10 Jan 2022 16:31 UTC)
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Re: Implementation of reduce-right in SRFI 1
Arthur A. Gleckler
(23 Oct 2022 01:45 UTC)
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Re: Implementation of reduce-right in SRFI 1
TAKIZAWA Yozo
(10 Jan 2022 11:54 UTC)
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Re: Implementation of reduce-right in SRFI 1 Alex Shinn 09 Jan 2022 23:20 UTC
This was from an issue first reported in Chibi. The definition of `reduce` is quite clear that it only uses the `ridentity` in the empty list case. It further provides a detailed note explaining this and the motivation. The definition of `reduce-right` both in the expansions given and the summary: "... in other words, we compute (fold-right f ridentity list)" seems to make it clear that the ridentity is used even in the non-empty list case. However, this makes no sense, because then there is no difference between fold-right and reduce-right. I think it's clear the same note was intended for reduce-right as for reduce. Also, the reduce-right definition incorrectly expands into reduce: (reduce-right f ridentity '(e1 e2 ...)) = (f e1 (reduce f ridentity (e2 ...))) At least there should be an errata to replace that expansion with `reduce-right`. Arguably it should be modified further: (reduce-right f ridentity '(e1 e2 ...)) = (fold-right f e1 (e2 ...)) updating the summary to something like "... in other words, we compute (fold-right f ridentity list), but as with reduce only use ridentity in the empty list case." -- Alex On Sun, Jan 9, 2022 at 1:48 AM Arthur A. Gleckler <xxxxxx@speechcode.com> wrote: > > On Tue, Dec 28, 2021 at 12:50 AM TAKIZAWA Yozo <xxxxxx@nbk.bz> wrote: >> >> Although this is not a specification topic but implementation, I send >> it to the list as a related issue to confirm or clarify. > > > Thanks for the question. Would you mind showing some examples to make the question clearer? It would be great if you could show examples that differ between Scheme implementations. > > Thanks, and happy new year.