Simon Peyton-Jones wrote:
I'm guessing a bit here, but it looks as if you intend this:
* GHC should read Foo.hs, and see {-# LANGUAGE CPP #-} * Then it should run cpp * Then it should look *again* in the result of running cpp, to see the now-revealed {-# LANGUAGE DeriveDataTypeable #-}
I'm pretty sure we don't do that; that is, we get the command-line flags once for all from the pre-cpp'd source code. Simon or Ian may be able to confirm.
Spot on.
If so, then this amounts to a) a documentation bug: it should be clear what GHC does
Right, I checked the docs and it doesn't explicitly say this.
b) a feature request, to somehow allow cpp to affect in-file flags I'm not sure what the spec would be
It needs a bit of thought - what should happen to pragmas that are there pre-CPP but not post-CPP, for example? Cheers, Simon
| -----Original Message----- | From: glasgow-haskell-users-bounces@haskell.org [mailto:glasgow-haskell-users- | bounces@haskell.org] On Behalf Of Alistair Bayley | Sent: Tuesday, February 10, 2009 12:03 PM | To: GHC Users Mailing List | Subject: Re: Pragma not recognised when wrapped in #ifdef | | > {-# LANGUAGE CPP #-} | > #ifdef PRAGMA_DERIVE_TYPEABLE | > {-# LANGUAGE DeriveDataTypeable #-} | > #else | > {-# OPTIONS -fglasgow-exts #-} | > #endif | > -- This file is Test/Fail.hs. | > -- ghc --make -optP-DPRAGMA_DERIVE_TYPEABLE -XCPP Test.Fail | > module Test.Fail where | > import Data.Generics | > data Fail = Fail deriving Typeable | > | > If compile this wih the command | > ghc --make -optP-DPRAGMA_DERIVE_TYPEABLE -XCPP Test.Fail | > then I get this error from ghc-6.10.1: | > | > [1 of 1] Compiling Test.Fail ( Test\Fail.hs, Test\Fail.o ) | > | > Test\Fail.hs:11:26: | > Can't make a derived instance of `Typeable Fail' | > (You need -XDeriveDataTypeable to derive an instance for this class) | > In the data type declaration for `Fail' | | | No response. I'd like to know if this is a bug (that's what it looks | like to me), or just a mistake I've made. | | Thanks, | Alistair | _______________________________________________ | Glasgow-haskell-users mailing list | Glasgow-haskell-users@haskell.org | http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
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