Re: [Haskell-cafe] Picking up the CI buildnumber during build

4 May 2018


      Vanessa McHale  writes:
...
Hi Magnus,
I would use getEnv
http://hackage.haskell.org/package/base-4.11.1.0/docs/System-Environment.htm...
or lookupEnv, along with Template Haskell and the runIO
http://hackage.haskell.org/package/template-haskell-2.13.0.0/docs/Language-H...
function. This would allow you to embed environment variables at 
compile
time.
Thanks! That were indeed the functions I was looking for. I ended 
up with
the following:

```haskell
import Data.Maybe (fromMaybe)
import Language.Haskell.TH (ExpQ, runIO, stringE)
import System.Environment (lookupEnv)

getBuildEnv :: String -> String -> ExpQ
getBuildEnv def varname = (runIO $ fromMaybe def <$> lookupEnv 
varname) >>= stringE
```

/M

--
Magnus Therning              OpenPGP: 0x927912051716CE39
email: magnus@therning.org   jabber: magnus@therning.org
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