diff options
Diffstat (limited to 'tv/5pkgs/haskell/th-env/src')
-rw-r--r-- | tv/5pkgs/haskell/th-env/src/THEnv.hs | 49 |
1 files changed, 49 insertions, 0 deletions
diff --git a/tv/5pkgs/haskell/th-env/src/THEnv.hs b/tv/5pkgs/haskell/th-env/src/THEnv.hs new file mode 100644 index 0000000..b04f2ce --- /dev/null +++ b/tv/5pkgs/haskell/th-env/src/THEnv.hs @@ -0,0 +1,49 @@ +{-# 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 |