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+module Arg where
+
+import Data.String (IsString)
+import GHC.Exts (IsList)
+import GHC.TypeLits (Symbol)
+
+-- | Wrap a function argument into this helper to give it a better description for the caller without disturbing the callsite too much.
+--
+-- This has instances for IsString and Num, meaning if the caller is usually a string or number literal, it should Just Work.
+--
+-- e.g.
+--
+-- @
+-- myFoo :: Arg "used as the name in error message" Text -> IO ()
+-- myFoo (Arg name) = …
+-- @
+--
+-- Will display the description in the inferred type of the callsite.
+--
+-- Due to IsString you can call @myFoo@ like
+--
+-- @myFoo "name in error"@
+--
+-- This is mostly intended for literals, if you want to wrap arbitrary data, use @Label@.
+newtype Arg (description :: Symbol) a = Arg {unArg :: a}
+  deriving newtype
+    ( Show,
+      Eq,
+      IsString,
+      IsList,
+      Num,
+      Monoid,
+      Semigroup
+    )