Hi Volker, You can use this extension: http://www.haskell.org/ghc/docs/latest/html/users_guide/deriving.html#stand-... to write that orphan Typeable instance for most ghcs (probably 6.10 is the earliest). It might be worth pushing for a Typeable instance to be added to the unix package (here: http://hackage.haskell.org/package/unix-2.7.0.1/docs/System-Posix-Process.ht..., with Carter's code): somebody else might define the same orphan instance too, which will break programs that end up seeing both instances. Regards, Adam On Tue, Aug 5, 2014 at 12:49 PM, Carter Schonwald wrote:

more concretely #if defined(__GLASGOW_HASKELL__) && ( __GLASGOW_HASKELL__ >= 707) --- do the deriving version here #else --- your current stuff #endif

On Tue, Aug 5, 2014 at 12:46 PM, Carter Schonwald wrote:

...

i assume 7.6 and 7.8, if we're talking GHC rather than GCC :)

in 7.8 you can't define userland typeable instances, you need only write deriving (Typeable) and you're all set. add some CPP to select the instances suitable

On Tue, Aug 5, 2014 at 12:41 PM, Volker Wysk wrote:

...

Hi!

I've been working with GHC-4.6.3, and updating to GHC-4.8.3 breaks my code,

because the Typeable class has been changed. The compiler produces this

message:

---------

src/HsShellScript/ProcErr.chs:2294:4:

‘typeOf’ is not a (visible) method of class ‘Typeable’

---------

I want to define System.Posix.Process.ProcessStatus to be an instance of

Typeable, so I can throw and catch it as an exception. ProcessStatus isn't

typeable by default.

Is it still possible to make ProcessStatus a member of Typeable? How?

Obviously, you can't accomplish it by deriving Typeable, because the definition

can't be changed any longer.

This is the spot in question:

----------

import System.Posix.Process

import Data.Typeable

{-

data ProcessStatus = Exited ExitCode

| Terminated Signal

| Stopped Signal

deriving (Eq, Ord, Show)

-}

instance Typeable ProcessStatus where

typeOf = const tyCon_ProcessStatus

tyCon_ProcessStatus = mkTyConApp (mkTyCon3 "hsshellscript"

"HsShellScript.ProcErr"

"Posix.ProcessStatus") []

instance Exception ProcessStatus

----------

Thanks,

V.W.

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Am Dienstag, 5. August 2014, 12:46:23 schrieb Carter Schonwald:

i assume 7.6 and 7.8, if we're talking GHC rather than GCC :)

in 7.8 you can't define userland typeable instances, you need only write deriving (Typeable) and you're all set. add some CPP to select the instances suitable

So you need to be able to change the definition of the data type, in order to add deriving (Typeable). It's not possible to add a Typeable instance declaration later. When you can't change the definition, you're out of luck. Okay, V.W.

thats what i meant. I meant you can't WRITE the body of a typeable in 7.8, you can derive though On Tue, Aug 5, 2014 at 1:59 PM, Brandon Allbery wrote:

On Tue, Aug 5, 2014 at 1:47 PM, Volker Wysk wrote:

...

Am Dienstag, 5. August 2014, 12:46:23 schrieb Carter Schonwald:

...

i assume 7.6 and 7.8, if we're talking GHC rather than GCC :)

in 7.8 you can't define userland typeable instances, you need only write deriving (Typeable) and you're all set. add some CPP to select the instances suitable

So you need to be able to change the definition of the data type, in order to add deriving (Typeable). It's not possible to add a Typeable instance declaration later.

Are you sure? There is a standalone deriving syntax.

deriving instance Typeable ProcessStatus

http://www.haskell.org/ghc/docs/latest/html/users_guide/deriving.html#stand-...

-- brandon s allbery kf8nh sine nomine associates allbery.b@gmail.com ballbery@sinenomine.net unix, openafs, kerberos, infrastructure, xmonad http://sinenomine.net

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If you can't change the definition you can use the syntax Björn Bringert added back in 2006 or so for StandaloneDeriving. Just turn on {-# LANGUAGE StandaloneDeriving, DeriveDataTypeable #-} and then you can use deriving instance Typeable Foo -Edward On Tue, Aug 5, 2014 at 1:47 PM, Volker Wysk wrote:

Am Dienstag, 5. August 2014, 12:46:23 schrieb Carter Schonwald:

...

i assume 7.6 and 7.8, if we're talking GHC rather than GCC :)

in 7.8 you can't define userland typeable instances, you need only write deriving (Typeable) and you're all set. add some CPP to select the instances suitable

So you need to be able to change the definition of the data type, in order to add deriving (Typeable). It's not possible to add a Typeable instance declaration later.

When you can't change the definition, you're out of luck.

Okay, V.W. _______________________________________________ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users