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-rw-r--r--tv/5pkgs/haskell/th-env/default.nix10
-rw-r--r--tv/5pkgs/haskell/th-env/src/THEnv.hs49
-rw-r--r--tv/5pkgs/haskell/th-env/th-env.cabal20
3 files changed, 79 insertions, 0 deletions
diff --git a/tv/5pkgs/haskell/th-env/default.nix b/tv/5pkgs/haskell/th-env/default.nix
new file mode 100644
index 000000000..474a63b85
--- /dev/null
+++ b/tv/5pkgs/haskell/th-env/default.nix
@@ -0,0 +1,10 @@
+{ mkDerivation, base, stdenv, template-haskell, text }:
+mkDerivation {
+ pname = "th-env";
+ version = "1.0.0";
+ src = ./.;
+ libraryHaskellDepends = [ base template-haskell text ];
+ homepage = "https://stackoverflow.com/q/57635686";
+ license = "unknown";
+ hydraPlatforms = stdenv.lib.platforms.none;
+}
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 000000000..b04f2ce0b
--- /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
diff --git a/tv/5pkgs/haskell/th-env/th-env.cabal b/tv/5pkgs/haskell/th-env/th-env.cabal
new file mode 100644
index 000000000..b9a2cff39
--- /dev/null
+++ b/tv/5pkgs/haskell/th-env/th-env.cabal
@@ -0,0 +1,20 @@
+name: th-env
+version: 1.0.0
+-- license: https://creativecommons.org/licenses/by-sa/4.0/
+license: OtherLicense
+author: https://stackoverflow.com/users/9348482
+homepage: https://stackoverflow.com/q/57635686
+maintainer: tv <tv@krebsco.de>
+build-type: Simple
+cabal-version: >=1.10
+
+library
+ hs-source-dirs: src
+ build-depends:
+ base,
+ template-haskell,
+ text
+ exposed-modules:
+ THEnv
+ default-language: Haskell2010
+ ghc-options: -O2 -Wall