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|
{-# LANGUAGE TemplateHaskell #-}
module THEnv
(
-- * Compile-time configuration
lookupCompileEnv
, lookupCompileEnvExp
, getCompileEnv
, getCompileEnvExp
, fileAsString
) where
import Control.Monad
import qualified Data.Text as T
import qualified Data.Text.IO as T
import Language.Haskell.TH
import Language.Haskell.TH.Syntax (Lift(..))
import System.Environment (getEnvironment)
-- Functions that work with compile-time configuration
-- | Looks up a compile-time environment variable.
lookupCompileEnv :: String -> Q (Maybe String)
lookupCompileEnv key = lookup key `liftM` runIO getEnvironment
-- | Looks up a compile-time environment variable. The result is a TH
-- expression of type @Maybe String@.
lookupCompileEnvExp :: String -> Q Exp
lookupCompileEnvExp = (`sigE` [t| Maybe String |]) . lift <=< lookupCompileEnv
-- We need to explicly type the result so that things like `print Nothing`
-- work.
-- | Looks up an compile-time environment variable and fail, if it's not
-- present.
getCompileEnv :: String -> Q String
getCompileEnv key =
lookupCompileEnv key >>=
maybe (fail $ "Environment variable " ++ key ++ " not defined") return
-- | Looks up an compile-time environment variable and fail, if it's not
-- present. The result is a TH expression of type @String@.
getCompileEnvExp :: String -> Q Exp
getCompileEnvExp = lift <=< getCompileEnv
-- | Loads the content of a file as a string constant expression.
-- The given path is relative to the source directory.
fileAsString :: FilePath -> Q Exp
fileAsString = do
-- addDependentFile path -- works only with template-haskell >= 2.7
stringE . T.unpack . T.strip <=< runIO . T.readFile
|
