Re: [Haskell-cafe] an idea for modifiyng data/newtype syntax: use `::=` instead of `=`

On 08 Aug 2015, at 23:11, Tom Ellis wrote:

On Sat, Aug 08, 2015 at 11:02:27PM +0200, MigMit wrote:

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What you say is "if we don't use some perfectly legitimate language constructs and never use third-party code, than 'data' and 'newtype' are the same".

No, not at all. I'm making a much stronger claim than that. I'm claiming the functionality provided by newtype is completely subsumed by that provided by data.

Well, it's certainly unsupported by evidence. Because third-party code CAN distinguish between those.

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On Sat, Aug 08, 2015 at 10:43:39PM +0200, MigMit wrote:

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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>>

Sure, they're not exactly the same thing but if you get the translations right you can use them for the same purposes:

Prelude> let y = case y of b -> B 1 in y B 1

I list the translations here

http://stackoverflow.com/questions/21327740/strict-single-constructor-single...

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