[Haskell-cafe] seq and lambda with patterns

[Denis Moskvin]

There is some subtle, but reasonable difference between \pat1 pat2 -> expr
and \pat1 -> \pat2 -> expr:

> seq ((\True y -> "DEFINED") undefined) 42
42
> seq ((\True -> \y -> "DEFINED") undefined) 42
*** Exception: Prelude.undefined

The reason is the translation from Haskell Report 2010 (3.3)
\ p1 . . . pn -> e = \ x1 . . . xn -> case (x1 , . . . , xn ) of (p1 , . .
. , pn ) -> e


Today I found (GHC 8.0.1) that

> seq ((\True -> \y -> undefined) undefined) 42
42

Is the last result correct?

-- 
Denis Moskvin
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