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author | makefu <github@syntax-fehler.de> | 2020-10-23 21:02:02 +0200 |
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committer | makefu <github@syntax-fehler.de> | 2020-10-23 21:02:02 +0200 |
commit | e8b6cc0587929a7ebd0d00f83d298640b20b055f (patch) | |
tree | e0f813b8264119a84d6b8c32fa68041c8541ab59 /tv/5pkgs/haskell/th-env/src/THEnv.hs | |
parent | fd41a76d4cab2765f9ef95ce5322b7bffe52b8a7 (diff) | |
parent | 242530680d5dcb37a5a023d0b8f6155ab441cead (diff) |
Merge remote-tracking branch 'lass/master'
Diffstat (limited to 'tv/5pkgs/haskell/th-env/src/THEnv.hs')
-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 00000000..b04f2ce0 --- /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 |