[Haskell-cafe] How to add use custom preprocessor in cabal

[Bernd Brassel]

Hi folks,

I am trying to integrate my own preprocessor into a cabal build
process. But there are several points that I get stuck with. Could
someone help me, please?

A simplification of my problem:
I have files "Abc.foo" and each of them should be transformed into
"Abc.hs" by calling function "transform". The resulting "Abc.hs" files
should then be exposed as Haskell library modules.

1. Question: How do I tell cabal that the file Abc.foo belongs to the
package?
After reading the User's Guide I had the impression that I should
write something like

Library
Eposed-Modules:
Abc.foo

But this leads to a parse error.

Adding a

Data-Files:
Abc.foo

to the heading, on the other hand, does not seem to do anything.

2. Question: How to add the preprocessor? I have tried

main =
defaultMainWithHooks
simpleUserHooks{hookedPreProcessors=[("foo",transformation)]}

transformation :: BuildInfo -> LocalBuildInfo -> PreProcessor

But under which circumstances will this function be called? Up to now
I have not succeeded in making cabal call this function.

Thanks for your time!
Bernd

[Duncan Coutts]

Post by Bernd Brassel
Hi folks,
I am trying to integrate my own preprocessor into a cabal build
process. But there are several points that I get stuck with. Could
someone help me, please?
I have files "Abc.foo" and each of them should be transformed into
"Abc.hs" by calling function "transform". The resulting "Abc.hs" files
should then be exposed as Haskell library modules.
1. Question: How do I tell cabal that the file Abc.foo belongs to the
package?
After reading the User's Guide I had the impression that I should
write something like
Library
Abc.foo
But this leads to a parse error.

Use

Library
Exposed-Modules:
Abc

It is a list of modules, not files.

Post by Bernd Brassel
Adding a
Abc.foo
to the heading, on the other hand, does not seem to do anything.

Right, those are for files that will be installed with the app and used
at runtime.

Post by Bernd Brassel
2. Question: How to add the preprocessor? I have tried
main =
defaultMainWithHooks
simpleUserHooks{hookedPreProcessors=[("foo",transformation)]}
transformation :: BuildInfo -> LocalBuildInfo -> PreProcessor

That looks right. Here's how to complete it (example taken from the
Cabal haddock docs for the PreProcess module):

transformation _ _ =
PreProcessor {
platformIndependent = True,
runPreProcessor =
mkSimplePreProcessor $ \inFile outFile verbosity -> do
fail $ "transformation: " ++ inFile ++ " " ++ outFile
}

and it works fine:

runghc Setup.hs build
Preprocessing library foo-1.0...
Setup.hs: transformation: Abc.foo dist/build/Abc.hs

Post by Bernd Brassel
But under which circumstances will this function be called? Up to now
I have not succeeded in making cabal call this function.

It calls it when it goes and looks for the module Abc (ie Abc.hs
or .lhs), and since if does not find it, it'll check through the list of
preprocessors and go looking for the corresponding files, ie Abc.foo.

Duncan