feat(users/Profpatsch/MyPrelude): add Arg r/8137

Change-Id: I218562c924489ff9cba783dc88ecb8e777c8aac3
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11656
Reviewed-by: Profpatsch <mail@profpatsch.de>
Autosubmit: Profpatsch <mail@profpatsch.de>
Tested-by: BuildkiteCI

3 files changed, 36 insertions, 0 deletions

diff --git a/users/Profpatsch/my-prelude/default.nix b/users/Profpatsch/my-prelude/default.nix
index e445115416..4bca8ea49f 100644
--- a/users/Profpatsch/my-prelude/default.nix
+++ b/users/Profpatsch/my-prelude/default.nix
@@ -7,6 +7,7 @@ pkgs.haskellPackages.mkDerivation {
   src = depot.users.Profpatsch.exactSource ./. [
     ./my-prelude.cabal
     ./src/Aeson.hs
+    ./src/Arg.hs
     ./src/AtLeast.hs
     ./src/MyPrelude.hs
     ./src/Test.hs
diff --git a/users/Profpatsch/my-prelude/my-prelude.cabal b/users/Profpatsch/my-prelude/my-prelude.cabal
index 95a8399f37..2f7882a526 100644
--- a/users/Profpatsch/my-prelude/my-prelude.cabal
+++ b/users/Profpatsch/my-prelude/my-prelude.cabal
@@ -59,6 +59,7 @@ library
     exposed-modules:
       MyPrelude
       Aeson
+      Arg
       AtLeast
       Test
       Postgres.Decoder
diff --git a/users/Profpatsch/my-prelude/src/Arg.hs b/users/Profpatsch/my-prelude/src/Arg.hs
new file mode 100644
index 0000000000..a6ffa90924
--- /dev/null
+++ b/users/Profpatsch/my-prelude/src/Arg.hs
@@ -0,0 +1,34 @@
+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
+    )