#16291: Fixing associativity of FormalCompositeMap
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Reporter: sbesnier | Owner: sbesnier
Type: defect | Status: needs_review
Priority: major | Milestone: sage-6.3
Component: categories | Resolution:
Keywords: associativity | Merged in:
FormalCompositeMap | Reviewers:
Authors: Sébastien Besnier | Work issues:
Report Upstream: N/A | Commit:
Branch: | 198085bda26743ebcb442f3b70698c3055395cd1
u/sbesnier/ticket/16291 | Stopgaps:
Dependencies: |
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Comment (by pbruin):
Replying to [comment:9 defeo]:
> > What is the reasoning behind `head()` and `tail()`?
>
> That was my suggestion. I find ''first'' and ''second'' misleading, and
think they should be deprecated. ''head'' and ''tail'' are standard names
in functional languages, e.g. caml. Of course, this is standard
terminology for lists, where there is little ambiguity on who's the head
and who's the tail.
Actually, the moment when I read `head` and `tail`, I was reminded of
`car` and `cdr`, so that had the desired effect. 8-)
> As you point out, it is more confusing if you draw arrows, but ''first''
and ''last'' is no less confusing than ''first'' and ''second'' in my
opinion.
Forget what I said about introducing `last`, I was confused. (Well, we
could introduce it anyway, but just as "the last morphism in the
composition", not with the current meaning of `tail`.)
> We could keep ''head'' and ''tail'', but reverse them to be consistent
with arrow diagrams (who says ''head'' should be first in applicative
order? We are making up the terminology, anyway). Or maybe ''head'' and
''shaft'', this is even more figurative!
I think it sounds nice, but `shaft` might be a bit annoying for people who
don't think of morphisms as arrows. And I would expect `head` to be the
''last'' morphism in the composition, not the composition of all except
the first.
> Or, if we want to stick with the applicative order, what about ''first''
and ''then''?
I like this idea, because it is close to the existing terminology and
because `then` is nicely consistent with the way composed morphisms are
printed.
> Whatever we choose, I think we should take names that sound ridiculous
enough to force the user to read the docstring, rather than say "I know
what that means".
I don't know, at the same time they should preferably also be of the kind
that you remember once you have seen them. And they shouldn't be so
ridiculous that they become distracting.
I'm starting to think that altogether `first` and `then` suggests itself
as the preferred choice.
--
Ticket URL: <http://trac.sagemath.org/ticket/16291#comment:10>
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