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up vote 6 down vote favorite
1

Is it possible somehow to configure cabal project to use different compiler than GHC? Additional is it possible to control this by some flags?

I want to compile my project with GHC or Haste (to JavaScript) based on some compilation flags.

It would be ideal if I could set my cabal configuration or my custom script to do something like:

-- target JS
cabal configure --target=js
cabal build

-- target Native
cabal configure --target=native
cabal build
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2 Answers 2

up vote 5 down vote

To build a Cabal project with either GHC or Haste, use the cabal binary for the former, and haste-inst (comes with haste) for the latter.

To have conditional code in in your modules, add {-# LANGUAGE CPP #-} and use #ifdef __HASTE__, which will only be defined by haste, but not by GHC. Note that __GLASGOW_HASKELL__ is defined in both cases (which makes sense, as haste builds on GHC for large parts of the compilation). So you would use it like

{-# LANGUAGE CPP #-}

module Module where

compiler :: String
#ifdef __HASTE__
compiler = "haste"
#else
compiler = "GHC"
#endif

Theoretically, for conditional settings in the Cabal file something like this should work:

library
  exposed-modules:
        Module
  if impl(ghc)
        exposed-modules:
                Module.GHC
  if impl(haste)
        exposed-modules:
                Module.GHC
  build-depends:       base ==4.6.*

but it seems that even with haste-inst, impl(ghc) is true; bug report is filed.

share|improve this answer
    
Thank you! Can I use different project.cabal options also? In the code I can use #ifdef and I want for example the JS version not to have the build-depends of graphviz? – Wojciech Danilo Jul 12 '13 at 17:09
    
additional - does {-# LANGUAGE CPP #-} is somehow connected with the ghc cpp backend? I want to use the LLVM backend. – Wojciech Danilo Jul 12 '13 at 17:10
    
@danilo2 To answer the second question: the CPP pragma doesn't have to do anything with C++. It allows one to use the C preprocessor -- aka "cpp". The cpp only does conditional preprocessing (including or excluding parts of code) using #if and #ifdef, but normally (in the case of Haskell) doesn't influence compilation itself. – phg Jul 12 '13 at 18:19
    
@phg I understand I cannot create C preprocessor macros with this pragma? – Wojciech Danilo Jul 12 '13 at 18:21
    
My answer was partially incorrect, corrected that. @danilo2: For different Cabal options, see the linked bug report. – Joachim Breitner Jul 13 '13 at 14:00
up vote 0 down vote

While it's currently not possible to use impl(haste) in your cabal files, you can now check for flag(haste-inst) to see if your package is being built using haste-inst.

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