feat(users/Profpatsch): init haskell exec-helpers

Mirrors the rust exec-helpers

Change-Id: I8fba49525949a8f38ca8c215e2ec7ba9d97d3bf9
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6116
Tested-by: BuildkiteCI
Reviewed-by: Profpatsch <mail@profpatsch.de>

users/Profpatsch/execline/ExecHelpers.hs

@@ -0,0 +1,48 @@
+{-# LANGUAGE DerivingStrategies #-}
+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE QuasiQuotes #-}
+{-# LANGUAGE TypeApplications #-}
+
+module ExecHelpers where
+
+import Data.String (IsString)
+import MyPrelude
+import qualified System.Exit as Sys
+
+newtype CurrentProgramName = CurrentProgramName { unCurrentProgramName :: Text }
+  deriving newtype (Show, Eq, Ord, IsString)
+
+-- | Exit 1 to signify a generic expected error
+-- (e.g. something that sometimes just goes wrong, like a nix build).
+dieExpectedError :: CurrentProgramName -> Text -> IO a
+dieExpectedError = dieWith 1
+
+-- | Exit 100 to signify a user error (“the user is holding it wrong”).
+--  This is a permanent error, if the program is executed the same way
+-- it should crash with 100 again.
+dieUserError :: CurrentProgramName -> Text -> IO a
+dieUserError = dieWith 100
+
+-- |  Exit 101 to signify an unexpected crash (failing assertion or panic).
+diePanic :: CurrentProgramName -> Text -> IO a
+diePanic = dieWith 101
+
+-- | Exit 111 to signify a temporary error (such as resource exhaustion)
+dieTemporary :: CurrentProgramName -> Text -> IO a
+dieTemporary = dieWith 111
+
+-- |  Exit 126 to signify an environment problem
+-- (the user has set up stuff incorrectly so the program cannot work)
+dieEnvironmentProblem :: CurrentProgramName -> Text -> IO a
+dieEnvironmentProblem = dieWith 126
+
+-- | Exit 127 to signify a missing executable.
+dieMissingExecutable :: CurrentProgramName -> Text -> IO a
+dieMissingExecutable = dieWith 127
+
+dieWith :: Natural -> CurrentProgramName -> Text -> IO a
+dieWith status currentProgramName msg = do
+  putStderrLn [fmt|{currentProgramName & unCurrentProgramName}: {msg}|]
+  Sys.exitWith
+    (Sys.ExitFailure (status & fromIntegral @Natural @Int))