[Haskell-cafe] Implicit concatenation in list comprehensions
greenrd at greenrd.org
Sun Jul 19 11:41:50 EDT 2009
I really like tuple sections and I've wanted them for years. I never use
comprehensions though, so I abstain from the other vote.
On Sun, 19 Jul 2009 08:18:48 -0700
Thomas Hartman <tphyahoo at gmail.com> wrote:
> I vote for tuple sections. Very nice!
> I don't really see immediate places where I would use the list
> comprehension improvement so I guess I don't vote for that.
> 2009/7/19 Neil Mitchell <ndmitchell at gmail.com>:
> > Hi Max,
> >> For fun, I spent a few hours yesterday implement support for this
> >> syntax in GHC, originally propsed by Koen Claessen:
> >>>>> [k, "=", v, " " | (k, v) <- [("foo", "1"), ("bar", "2")]
> >> ["foo", "=", "1", " ", "bar", "=", "2", " "]
> >> This is a generalisation of list comprehensions that allows several
> >> items to be concatenated onto the result list at once, by having
> >> several comma-separated items before the pipe.
> > I like the power this feature gives, and if it was already in
> > Haskell 98 I'd certainly have used it a few times. I can't think of
> > anything else the syntax could mean, so I don't see a potential for
> > it stealing syntax that might otherwise be reused. However, it
> > doesn't seem that discoverable or natural - I'm not sure I'd have
> > ever guessed that such a feature might exist.
> >> P.S. I also implemented tuple sections
> >> (http://hackage.haskell.org/trac/ghc/ticket/3377#comment:3) which
> >> are a lot more useful:
> > Yay! Discoverable, useful and really common in practice - a
> > brilliant extension :-)
> > Thanks
> > Neil
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