Sorry, should be `cabal install --flags="ghc7" package-name`. On Sun, Nov 28, 2010 at 1:59 AM, Jinjing Wang wrote:

Thanks Michael,

So the user should use `cabal install --flags -ghc7 package-name` to install the package, if I'm not mistaken?

Will it work if the package is installed as a dependency? Will the flag environment be passed down from the root package?

Is there a way to detect GHC version automatically?

: )

Best,

On Sun, Nov 28, 2010 at 1:32 AM, Michael Snoyman wrote:

...

On Sat, Nov 27, 2010 at 6:59 PM, Jinjing Wang wrote:

...

Dear list,

...

From ghc 7.0.1 release notes:

...

The Language.Haskell.TH.Quote.QuasiQuoter type has two new fields: quoteType and quoteDec.

Some of my code needs to be conditionally compiled to support both version 6 and 7, what is the recommended way to do it?

ref:

* http://new-www.haskell.org/ghc/docs/7.0.1/html/users_guide/release-7-0-1.htm...

Hi Jinjing,

I've done this in Yesod. I'm not sure if it's the best way, but basically I've added a ghc7 flag to the cabal file, and a block for the library that reads:

   if flag(ghc7)        build-depends:   base                      >= 4.3      && < 5        cpp-options:     -DGHC7    else        build-depends:   base                      >= 4        && < 4.3

Then whenever I want to quasi-quote in the code, I write:

#if GHC7    [quasiquoter| #else    [$quasiquoter| #endif

Michael

-- jinjing

-- jinjing

On Sat, Nov 27, 2010 at 9:59 AM, Jinjing Wang wrote:

Thanks Michael,

So the user should use `cabal install --flags -ghc7 package-name` to install the package, if I'm not mistaken?

Will it work if the package is installed as a dependency? Will the flag environment be passed down from the root package?

Is there a way to detect GHC version automatically?

I see that others have provided answers on here, but another way is to change the check from: if flag(ghc7) build-depends: base >= 4.3 && < 5 cpp-options: -DGHC7 else build-depends: base >= 4 && < 4.3 to this: if impl(ghc >= 7) build-depends: base >= 4.3 && < 5 cpp-options: -DGHC7 else build-depends: base >= 4 && < 4.3 I hope that helps, Jason

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 12/5/10 17:05 , Henning Thielemann wrote:

Isn't it better to move the dependency on 'base' out of the If block? I mean, someone might succeed to use GHC-7 with base-4.2 or GHC<7 or a different compiler with base-4.3.

Since the base package is (with good reason) part of the compiler, anyone smart enough to get that to work is smart enough to edit the cabal file. - -- brandon s. allbery [linux,solaris,freebsd,perl] allbery@kf8nh.com system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.10 (Darwin) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAkz8GukACgkQIn7hlCsL25WTxACfc4k/3GoQr402TbVFmabRD7sJ 7WEAoMnmLeaKGfjQdjdP4K60Ch6g72md =LZuU -----END PGP SIGNATURE-----

On Sat, Nov 27, 2010 at 9:41 PM, Antoine Latter wrote:

On Sat, Nov 27, 2010 at 10:59 AM, Jinjing Wang wrote:

...

Dear list,

...

From ghc 7.0.1 release notes:

...

The Language.Haskell.TH.Quote.QuasiQuoter type has two new fields: quoteType and quoteDec.

Some of my code needs to be conditionally compiled to support both version 6 and 7, what is the recommended way to do it?

ref:

* http://new-www.haskell.org/ghc/docs/7.0.1/html/users_guide/release-7-0-1.htm...

Can you just not set those fields? Then the code should work as-is for both versions. You'll get warnings for GHC 7, I think.

Sorry Jinjing, I didn't read your original email carefully enough. Antoine is absolutely correct, this is the better way to deal with defining a quasiquoter. My suggestion is only necessary if you want to *use* a quasiquoter. Michael

On Sat, Nov 27, 2010 at 8:38 PM, Jinjing Wang wrote:

Hi Michael, you are absolutely correct, cabal did set the flags automatically.

To sum up, here's what needs to be done:

* add `flag ghc7` as a field in cabal * add:

   if flag(ghc7)        build-depends:   base                      >= 4.3      && < 5        cpp-options:     -DGHC7    else        build-depends:   base                      >= 4        && < 4.3

  in library field in cabal

* add `{-# LANGUAGE CPP #-}` in source file * add

   #if GHC7    x

   #else    y

   #endif

 Hi Antonine, I don't know how to not set those fields in the constructor.. as a QQ noob, I'm just hacking on some legacy code. This code doesn't compile in GHC7, so I have to do this trick.

* https://github.com/nfjinjing/mps/blob/master/src/MPS/TH.hs

Something like: myQuoter = QuasiQuoter { quoteExp = expQuoter, quotePat = patQuoter } Will work in either version, but it will leave the un-set fields set to `undefined`, so you'll get a compile error if you try to use them. I haven't tested this, but I've done it with other record types. Take care, Antoine

Hi Antoine, Thanks for pointing out, it did work. By using a record style constructor, the code can be made to support both version, something like here = QuasiQuoter { quoteExp = (litE . stringL) , quotePat = (litP . stringL) } in GHC7 there's a warning: Warning: Fields of `QuasiQuoter' not initialised: quoteType, quoteDec So far it works without problem. On Sun, Nov 28, 2010 at 10:38 AM, Jinjing Wang wrote:

Hi Michael, you are absolutely correct, cabal did set the flags automatically.

To sum up, here's what needs to be done:

* add `flag ghc7` as a field in cabal * add:

   if flag(ghc7)        build-depends:   base                      >= 4.3      && < 5        cpp-options:     -DGHC7    else        build-depends:   base                      >= 4        && < 4.3

  in library field in cabal

* add `{-# LANGUAGE CPP #-}` in source file * add

   #if GHC7    x

   #else    y

   #endif

 Hi Antonine, I don't know how to not set those fields in the constructor.. as a QQ noob, I'm just hacking on some legacy code. This code doesn't compile in GHC7, so I have to do this trick.

* https://github.com/nfjinjing/mps/blob/master/src/MPS/TH.hs

Best,

On Sun, Nov 28, 2010 at 3:48 AM, Michael Snoyman wrote:

...

On Sat, Nov 27, 2010 at 9:41 PM, Antoine Latter wrote:

...

On Sat, Nov 27, 2010 at 10:59 AM, Jinjing Wang wrote:

...

Dear list,

...

From ghc 7.0.1 release notes:

...

The Language.Haskell.TH.Quote.QuasiQuoter type has two new fields: quoteType and quoteDec.

Some of my code needs to be conditionally compiled to support both version 6 and 7, what is the recommended way to do it?

ref:

* http://new-www.haskell.org/ghc/docs/7.0.1/html/users_guide/release-7-0-1.htm...

Can you just not set those fields? Then the code should work as-is for both versions. You'll get warnings for GHC 7, I think.

Sorry Jinjing, I didn't read your original email carefully enough. Antoine is absolutely correct, this is the better way to deal with defining a quasiquoter. My suggestion is only necessary if you want to *use* a quasiquoter.

Michael

-- jinjing

-- jinjing

On Wed, Dec 1, 2010 at 4:07 AM, Thomas Schilling wrote:

I think a nicer way to solve that issue is to use Cabal's MIN_VERSION macros.

 1. Add CPP to your extensions.  This will cause cabal to auto-generate a file with MIN_VERSION_<pkg> macros for each <pkg> in build-depends.

 2. GHC 6.12.* comes with template-haskell 2.4, so to test for that use:

#ifdef MIN_VERSION_template_haskell(2,4,0)  .. ghc-6.12.* code here. #endif

This should make it more transparent to the user.

This is obviously a personal preference issue, but I try to avoid the Cabal macros since they don't let my code run outside the context of Cabal. I often times like to have a test suite that I can just use with runhaskell, and (unless you can tell me otherwise) I can't run it anymore. Also, I think #if GHC7 ... #endif is more transparent than a check on template-haskell. Michael

On Wed, Dec 1, 2010 at 6:58 PM, Claus Reinke wrote:

...

This is obviously a personal preference issue, but I try to avoid the Cabal macros since they don't let my code run outside the context of Cabal. I often times like to have a test suite that I can just use with runhaskell, and (unless you can tell me otherwise) I can't run it anymore.

Also, I think

#if GHC7 ... #endif

is more transparent than a check on template-haskell.

Just in case this hasn't been mentioned yet: if you want to be independent of cabal, there is the old standby

__GLASGOW_HASKELL__ http://haskell.org/ghc/docs/latest/html/users_guide/options-phases.html#c-pr...

Well, I think this is the official right approach. I was not aware of that, thank you Claus. Michael