Adding dup to Data.Tuple?

[Edward Kmett]

I have no strong preference for the name for 'jam', merely the existence of
the dual construction if we're going to name one.

However a needless name conflict with duplicate from Control.Comonad would
be rather unfortunate.

dup as the name for this operation has a ton of precedent in languages like
forth, and its length is comparable to the already smashed fst and snd.

-Edward


On Sun, Oct 28, 2018 at 6:15 PM Oliver Charles <ollie at ocharles.org.uk>
wrote:

> jam? Seriously? I'm sure we can do much better wrt names than that.
> Even dup I'd rather see expanded to "duplicate". The theory might have
> shown that these are useful combinators, but that doesn't mean they
> should decide the names.
> On Sun, Oct 28, 2018 at 10:10 PM Edward Kmett <ekmett at gmail.com> wrote:
> >
> > If we're going to add this we should add the symmetric operation for
> >
> > jam :: Either a a -> a
> >
> > to Data.Either. (Name taken from Conal's compiling to categories code.)
> >
> > My own code has called these diag and codiag respectively. I happily
> yield to a nicer convention.
> >
> > I have no real preference for whether we do the simple version in
> Data.Tuple (which has a lot of precedent, as Data.Tuple tends to have lots
> of little simple combinators that could be done more generally as arrows)
> or moving it into Control.Arrow.
> >
> > -Edward
> >
> > On Sun, Oct 28, 2018 at 12:07 PM Ivan Perez <ivan.perez at keera.co.uk>
> wrote:
> >>
> >> On 28/10/18 09:48, Vanessa McHale wrote:
> >> > According to GHCi,
> >> >
> >> > λ:> import Control.Arrow
> >> > λ:> :t (id &&& id)
> >> > (id &&& id) :: b -> (b, b)
> >> >
> >> > That is, this implementation has type a -> (a, a) as well.
> >> Yes, yes, that's what I meant by "it works for functions as well (since
> >> they are arrows)"
> >>
> >> Ivan
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