Re: [Haskell-cafe] lambda case
Brandon Allbery writes:
> On Sat, Dec 1, 2012 at 5:30 AM, Roman Cheplyaka wrote:
>
>> I find this discussion useful — there are some interesting points
>> (splitting "case of" into two parts) that I don't remember reading in the
>> original thread (but maybe it's just me).
>>
>
> Mentioned twice that I recall, as treating 'of' as a lambda and as '\of'.
I’m not quite sure what treating “of” as lambda means, and \of
raises the some of the same objections as \case.
Up until the introduction of “lambda-case”, \ was a clear
indication that what was coming next was a pattern that would
bind variables (except in degenerate cases, but anyone who
writes something like \Nothing -> e should be taken out and sho-
wn why it’s a bad idea).
> It got somewhat short shrift, likely because while it makes sense from an
> existing language syntax viewpoint, it makes little to none from a
> readability standpoint.
Of the available alternatives, it makes the most linguistic
sense. If you can’t read the subtext for that sentence, try
again :-) In the design I was suggesting, “of” is in no sense a
lambda, it simply introduces a list of alternative patterns
exactly as it does in the original design of case … of {alts}.
Arguing about whether “of” is the right keyword here without
arguing that case… of… should have different keywords is
inconsistent, and arguing for a change of those keywords really
would be fussing about the colour of the bikeshed after it was
painted.
--
Jón Fairbairn jon.fairba...@cl.cam.ac.uk
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Re: [Haskell-cafe] lambda case
On Sat, Dec 1, 2012 at 5:30 AM, Roman Cheplyaka wrote: > I find this discussion useful — there are some interesting points > (splitting "case of" into two parts) that I don't remember reading in the > original thread (but maybe it's just me). > Mentioned twice that I recall, as treating 'of' as a lambda and as '\of'. It got somewhat short shrift, likely because while it makes sense from an existing language syntax viewpoint, it makes little to none from a readability standpoint. -- brandon s allbery kf8nh sine nomine associates allber...@gmail.com ballb...@sinenomine.net unix, openafs, kerberos, infrastructure, xmonadhttp://sinenomine.net ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: [Haskell-cafe] lambda case
It hasn't made it to the standard yet, though. If some experimental
feature is implemented in GHC, it doesn't mean it's set in stone.
I find this discussion useful — there are some interesting points
(splitting "case of" into two parts) that I don't remember reading in the
original thread (but maybe it's just me).
Roman
* Brent Yorgey [2012-11-30 09:52:53-0500]
> Oh, PLEASE people. Let's not have another round of bikeshedding about
> this AFTER the feature is already implemented!
>
> -Brent
>
> On Fri, Nov 30, 2012 at 01:25:27PM +0100, Herbert Valerio Riedel wrote:
> > Jon Fairbairn writes:
> >
> > [...]
> >
> > > “\case” complicates lambda, using “of” simply breaks “case … of …”
> > > into two easily understood parts.
> >
> > Just some observation (I'm rather late to the lambda-case discussion, so
> > this might have been already pointed out previously):
> >
> > if the reserved keyword 'of' was to take the place of '\case', shouldn't
> > then
> >
> > 'case' exp
> >
> > w/o the "'of' { alts }"-part become a separately valid expression (with
> > 'case' essentially meaning 'flip ($)') to really break it up into two
> > independent parts? Then 'case exp of { alts }' wouldn't be a special
> > form anymore, but would just result from combining 'case' and 'of';
> >
> > 'case' wouldn't even need to be a reserved keyword (and thus the grammar
> > could be simplified), if it wasn't for the current grammar which
> > requires to isolate a \case-expression by using () or $, consider e.g.:
> >
> > {-# LANGUAGE LambdaCase #-}
> >
> > import System.Environment
> >
> > case' :: b -> (b -> c) -> c
> > case' = flip ($)
> >
> > main = do
> > s <- getArgs
> >
> > case' s $ \case -- image '\case' was actually '\of' or 'of'
> > [x] -> putStrLn ("Hello " ++ x)
> > _ -> putStrLn "wrong number of arguments given"
> >
> >
> > just my 2¢
> >
> > cheers,
> > hvr
> >
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