Re: cabal: question on compiling build prerequisites

Hi Dag, this was a good suggestion, but it doesn't work. When invoking this preprocessor, GHC will run the command runghc <source> <input> <output> PreProc. In other words, any options specified with -optF are appended at the *end* of the preprocessor arguments, not the beginning. So one can never use runghc to run a proprocessor. Thanks, -- Peter Dag Odenhall wrote:

How about -pgmF runghc -optF PreProc?

On Mon, Dec 9, 2013 at 12:48 AM, Peter Selinger wrote:

...

Thanks for the suggestion! However, it is not portable: it doesn't work on Windows.

Similarly, giving "runhaskell ./PreProc.hs" as the preprocessor command to GHC doesn't work either, because GHC will try to run a program with that exact name (including the space), rather than interpreting it as a command with an argument.

In addition, even on Posix systems, where the above method does work, it is nevertheless extremely slow: runhaskell will have to interpret or compile ./PreProc.hs separately for each source file, of which there could be many.

Another solution I thought of is to include

import Preproc

at the beginning of Setup.hs. This way compiling Setup.hs would have the side effect of compiling Preproc.hs. It would not work with the "runhaskell Setup.hs" method, though.

-- Peter

Erik Hesselink wrote:

...

On Sun, Dec 8, 2013 at 7:50 PM, Peter Selinger

...

...

thanks for your reply! So say my package directory contains two files:

Test.hs PreProc.hs

What you are suggesting is:

ghc Test.hs -F -pgmF ./PreProc

However, this gives the error message:

ghc: could not execute: ./PreProc

And indeed, while GHC is smart enough to automatically run a preprocessor, it is not smart enough to automatically *compile* the preprocessor. So it needs to be compiled beforehand, which would be Cabal's job.

Not per se. You could try making it executable, and prepending a line

wrote: like:

...

#!/usr/bin/env runhaskell

That way you can run your preprocessor like a script, without compiling

it.

...

Erik

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