You'll need to change the `cpp-options` field in your .cabal file. You can do this conditionally by using a cabal flag. On 06/20/2018 02:16 AM, PY wrote:

Hello all,

I'm using conditional compilation:

#ifdef BLAH   blahBlah   #endif

And I want to define BLAH, but not in *.hs file. For example, with `stack` option or as environment variable... How can I do it? For example, `stack -DBLAH=1 build` or something else. I tried

  stack build --flag='*:BLAH'

- no effect.

Also I tried

  stack build --flag=my-library:BLAH

and get error that my-library package does not define flag BLAH. So, it's total secret for me how to make such thing (like we can do with gcc, make, etc)  :-)

===

Best regards, Paul

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