#5529: Newtypes with hidden constructors cannot be passed as FFI arguments
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Reporter: mikhail.vorozhtsov | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 7.3
Keywords: | Testcase:
Blockedby: | Difficulty:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: None/Unknown
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Comment(by simonpj):
I can see merit in Mkhail's point of view.
Example
{{{
module Colours( Colour, red, draw ) where
newtype Colour = C Int
red :: Colour
red = 7
foreign import "draw" :: Colour -> IO ()
}}}
The question is whether this should be legal
{{{
module Foo where
import Colours
foriegn import "draw2" :: Colour -> IO ()
}}}
That is, a client of `Colours` can call a `draw2` function that unpacks
the `Colour`. Or should the abstract data type `Colour` be restricted to
the functions (foreign or otherwise) that `Colours` exports?
I don't have a strong opinion. Did we make the change in response to a bug
report? Ie was someone arguing the opposite?
Simon
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5529#comment:1>
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