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

[Magnus Therning]

Vanessa McHale <vanessa.mchale at iohk.io> writes:

> Hi Magnus,
>
> I would use getEnv
> <http://hackage.haskell.org/package/base-4.11.1.0/docs/System-Environment.html#v:getEnv>
> or lookupEnv, along with Template Haskell and the runIO
> <http://hackage.haskell.org/package/template-haskell-2.13.0.0/docs/Language-Haskell-TH-Syntax.html#v:runIO>
> 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 at therning.org   jabber: magnus at therning.org
twitter: magthe               http://therning.org/magnus

Ah, good taste! What a dreadful thing! Taste is the enemy of
creativeness.
     — Pablo Picasso
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