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-rw-r--r--tv/5pkgs/haskell/th-env/src/THEnv.hs49
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
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+++ b/tv/5pkgs/haskell/th-env/src/THEnv.hs
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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