Re: [Haskell-cafe] Re: proposal: point free case expressions

2009/11/5 Edward Kmett :

On Thu, Nov 5, 2009 at 10:59 AM, Stefan Monnier wrote:

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We could really use a case statement in which we skip the scrutinee and make (case of {})' be syntactic sugar for `(\x -> case x of {})'.

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So we could write:

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myFunc = anotherFunc $ case of Left err -> print err Right msg -> putStrLn msg

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A minor syntactical addition, a big win!

Since this "case" really defines a function, it seems like it would make more sense to allow defining anonymous functions by pattern matching. I.e. instead of "case of", I think it should use "λ", "\", "fn", or ...

The problem with all of those options is that they introduce a new keyword into the language and can potentially break existing code.

Eugene's \{ } avoids that by using a different hole in the grammar, but at the expense of 'un-Haskelly' braces. That and I question how easy it would be to get to parse, because a common idiom seems to be to parse patterns as expressions before converting them to patterns to avoid certain other ambiguities in the grammar, so this requires a { } expression, which may introduce a lot more ambiguity and problems to the grammar than it would seem at first glance.

Hey, the braces are not that un-Haskelly. After all, you already can write "case x of {Left err -> ...; Right res -> ...}" - that's exactly why I suggested this notation. So, I am just suggesting to replace "case of" with "\" and that's all.

-Edward Kmett

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