home-grown pretty printer for term -- Poly/ML 5.3.0 does not observe infix status of constructors (notably $);

--- a/src/Pure/ML-Systems/install_pp_polyml-5.3.ML	Tue Nov 10 09:22:55 2009 +0000
+++ b/src/Pure/ML-Systems/install_pp_polyml-5.3.ML	Tue Nov 10 13:05:35 2009 +0100
@@ -15,3 +15,29 @@
   | SOME (Exn.Exn _) => PolyML.PrettyString "<failed>"
   | SOME (Exn.Result y) => pretty (y, depth)));
 
+PolyML.addPrettyPrinter (fn depth => fn _ => fn tm =>
+  let
+    open PolyML;
+    val from_ML = Pretty.from_ML o pretty_ml;
+    fun prt_app name prt = Pretty.block [Pretty.str (name ^ " "), prt];
+    fun prt_apps name = Pretty.enum "," (name ^ " (") ")";
+    fun prt_term parens dp (t as _ $ _) =
+          op :: (strip_comb t)
+          |> map_index (fn (i, u) => prt_term true (dp - i - 1) u)
+          |> Pretty.separate " $"
+          |> (if parens then Pretty.enclose "(" ")" else Pretty.block)
+      | prt_term _ dp (Abs (x, T, body)) =
+          prt_apps "Abs"
+           [from_ML (prettyRepresentation (x, dp - 1)),
+            from_ML (prettyRepresentation (T, dp - 2)),
+            prt_term false (dp - 3) body]
+      | prt_term _ dp (Const const) =
+          prt_app "Const" (from_ML (prettyRepresentation (const, dp - 1)))
+      | prt_term _ dp (Free free) =
+          prt_app "Free" (from_ML (prettyRepresentation (free, dp - 1)))
+      | prt_term _ dp (Var var) =
+          prt_app "Var" (from_ML (prettyRepresentation (var, dp - 1)))
+      | prt_term _ dp (Bound i) =
+          prt_app "Bound" (from_ML (prettyRepresentation (i, dp - 1)));
+  in ml_pretty (Pretty.to_ML (prt_term false depth tm)) end);
+