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Re: [PATCH] Elpa: Pinpoint semantics of `seq-subseq' for streams
From: |
Michael Heerdegen |
Subject: |
Re: [PATCH] Elpa: Pinpoint semantics of `seq-subseq' for streams |
Date: |
Tue, 13 Sep 2016 23:17:00 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/25.1 (gnu/linux) |
Hi Clément,
> On 2016-09-13 12:23, Michael Heerdegen wrote:
> > - Forbid negative index arguments.
>
> Do you really want to forbid negative arguments? Do we have a function
> akin to `tail' for streams (something that would return the last n
> elements?
Thanks for your feedback!
Yes, I want to forbid them, unless there are realistic use cases. No,
we don't have something like `tail' for streams. If you want something
like that, you are in general better done with lists (i.e. convert the
stream into a list), I think.
Streams are delayed. In general, you don't know how many (or if any at
all) elements a stream will generate later. All functions building
streams out of argument streams are not allowed to generate any elements
from any input stream.
Negative indexes for `seq-subseq' would still be possible without
breaking these rules - but you would probably not need the result to be
a stream anyway (instead of a list, for example). Streams are a mean to
program in a certain way (called data flow control or something like
that). Negative indexes for `seq-subseq' collide with this model.
That's why I thought it's better to forbid negative indexes for now. If
I see an example where it is really useful and appropriate, or good
arguments against this decision, I'll change my mind.
Regards,
Michael.
- [PATCH] Elpa: Pinpoint semantics of `seq-subseq' for streams, Michael Heerdegen, 2016/09/13
- Re: [PATCH] Elpa: Pinpoint semantics of `seq-subseq' for streams, Clément Pit--Claudel, 2016/09/13
- Re: [PATCH] Elpa: Pinpoint semantics of `seq-subseq' for streams,
Michael Heerdegen <=
- Re: [PATCH] Elpa: Pinpoint semantics of `seq-subseq' for streams, Clément Pit--Claudel, 2016/09/13
- Re: [PATCH] Elpa: Pinpoint semantics of `seq-subseq' for streams, Michael Heerdegen, 2016/09/14
- Re: [PATCH] Elpa: Pinpoint semantics of `seq-subseq' for streams, Clément Pit--Claudel, 2016/09/14
- Re: [PATCH] Elpa: Pinpoint semantics of `seq-subseq' for streams, John Mastro, 2016/09/14
- Re: [PATCH] Elpa: Pinpoint semantics of `seq-subseq' for streams, Clément Pit--Claudel, 2016/09/14
- Re: [PATCH] Elpa: Pinpoint semantics of `seq-subseq' for streams, John Mastro, 2016/09/15
- Re: [PATCH] Elpa: Pinpoint semantics of `seq-subseq' for streams, Michael Heerdegen, 2016/09/15
- Re: [PATCH] Elpa: Pinpoint semantics of `seq-subseq' for streams, Clément Pit--Claudel, 2016/09/15
- Re: [PATCH] Elpa: Pinpoint semantics of `seq-subseq' for streams, Michael Heerdegen, 2016/09/15
- Re: [PATCH] Elpa: Pinpoint semantics of `seq-subseq' for streams, Clément Pit--Claudel, 2016/09/15