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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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.Fairbairn@cl.cam.ac.uk