[Haskell-cafe] tuple and pattern synonym
Kazu Yamamoto (=?iso-2022-jp?B?GyRCOzNLXE9CSScbKEI=?=)
kazu at iij.ad.jp
Mon May 18 03:56:47 UTC 2020
Hi,
I have a question about PatternSynonyms. Suppose we have:
data Foo = Foo Int Int
I would like to define a pattern as follows:
pattern P :: (Int,Int) -> Foo
pattern P (x,y) = Foo x y
But this results in "parse error on input ‘(’". Are there any ways to
use tuple in the left side hand of patterns?
This is important to maintain backward compatibility for the "network"
library.
If there is no way, I will define Foo as:
data Foo = Foo (Int,Int) -- awkward
and define P as:
pattern P :: (Int,Int) -> Foo
pattern P xy = Foo xy
Regards,
--Kazu
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