[Haskell-cafe] an idea for modifiyng data/newtype syntax: use `::=` instead of `=`
miguelimo38 at yandex.ru
Sat Aug 8 21:32:59 UTC 2015
>>>> Well, it's certainly unsupported by evidence. Because third-party code CAN
>>>> distinguish between those.
>>> OK, show me the code!
>> I did. You removed it when quoting.
>>> Prelude> newtype A = A Int deriving Show
>>> Prelude> data B = B !Int deriving Show
>>> Prelude> let x = case x of A n -> A 1 in x
>>> A 1
>>> Prelude> let y = case y of B n -> B 1 in y
>>> *** Exception: <<loop>>
> This isn't third party code. It knows about the constructors of A and B.
1) This might be the code written by someone using your library/framework. In which case it would know about A and B.
2) It might be generated by the Template Haskell — which is free to use whatever constructor is fed into it.
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