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diff --git a/users/Profpatsch/whatcd-resolver/src/Tool.hs b/users/Profpatsch/whatcd-resolver/src/Tool.hs
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+{-# LANGUAGE QuasiQuotes #-}
+
+module Tool where
+
+import Data.Error.Tree
+import Label
+import PossehlAnalyticsPrelude
+import System.Environment qualified as Env
+import System.Exit qualified as Exit
+import System.FilePath ((</>))
+import System.Posix qualified as Posix
+import ValidationParseT
+
+data Tool = Tool
+  { -- | absolute path to the executable
+    toolPath :: FilePath
+  }
+  deriving stock (Show)
+
+-- | Reads all tools from the @toolsEnvVar@ variable or aborts.
+readTools ::
+  Label "toolsEnvVar" Text ->
+  -- | Parser for Tools we bring with us at build time.
+  --
+  -- These are executables that we need available, and that we have to ship with the distribution of @pa-cli@.
+  ToolParserT IO tools ->
+  IO tools
+readTools env toolParser =
+  Env.lookupEnv (env.toolsEnvVar & textToString) >>= \case
+    Nothing -> do
+      Exit.die [fmt|Please set {env.toolsEnvVar} to a directory with all tools we need (see `Tools` in the code).|]
+    Just toolsDir ->
+      (Posix.fileExist toolsDir & ifTrueOrErr () [fmt|{env.toolsEnvVar} directory does not exist: {toolsDir}|])
+        & thenValidate
+          ( \() ->
+              (Posix.getFileStatus toolsDir <&> Posix.isDirectory)
+                & ifTrueOrErr () [fmt|{env.toolsEnvVar} does not point to a directory: {toolsDir}|]
+          )
+        & thenValidate
+          (\() -> toolParser.unToolParser toolsDir)
+        <&> first (errorTree [fmt|Could not find all tools in {env.toolsEnvVar}|])
+        >>= \case
+          Failure err -> Exit.die (err & prettyErrorTree & textToString)
+          Success t -> pure t
+
+newtype ToolParserT m a = ToolParserT
+  { unToolParser ::
+      FilePath ->
+      m (Validation (NonEmpty Error) a)
+  }
+  deriving
+    (Functor, Applicative)
+    via (ValidationParseT FilePath m)
+
+-- | Given a file path and the name of the tool executable, see whether it is an executable and return its full path.
+readTool :: Text -> ToolParserT IO Tool
+readTool exeName = ToolParserT $ \toolDir -> do
+  let toolPath :: FilePath = toolDir </> (exeName & textToString)
+  let read' = True
+  let write = False
+  let exec = True
+  Posix.fileExist toolPath
+    & ifTrueOrErr () [fmt|Tool does not exist: {toolPath}|]
+    & thenValidate
+      ( \() ->
+          Posix.fileAccess toolPath read' write exec
+            & ifTrueOrErr (Tool {..}) [fmt|Tool is not readable/executable: {toolPath}|]
+      )
+
+-- | helper
+ifTrueOrErr :: Functor f => a -> Text -> f Bool -> f (Validation (NonEmpty Error) a)
+ifTrueOrErr true err io =
+  io <&> \case
+    True -> Success true
+    False -> Failure $ singleton $ newError err