optimizations to default rhs case, code cleanup

Author: zazedd

ppx_regexp/ppx_regexp.ml

@@ -55,14 +55,14 @@ let transformation ctx =
       let e_ext, acc = super#expression e_ext acc in
       let make_transformations ~mode ~opts ~loc = function
         | Pexp_function cases ->
-          let cases, bindings = Transformations.transform_cases ~mode ~opts ~loc ~ctx cases in
-          [%expr fun _ppx_regexp_v -> [%e cases]], bindings @ acc
+          let cases, binding = Transformations.transform_cases ~mode ~opts ~loc ~ctx cases in
+          [%expr fun _ppx_regexp_v -> [%e cases]], binding :: acc
         | Pexp_match (e, cases) ->
-          let cases, bindings = Transformations.transform_cases ~mode ~opts ~loc ~ctx cases in
+          let cases, binding = Transformations.transform_cases ~mode ~opts ~loc ~ctx cases in
           ( [%expr
               let _ppx_regexp_v = [%e e] in
               [%e cases]],
-            bindings @ acc )
+            binding :: acc )
         | _ -> Util.error ~loc "[%%pcre] and [%%mik] only apply to match, function and global let declarations of strings."
       in
       match e_ext.pexp_desc with

ppx_regexp/transformations.ml

@@ -167,7 +167,11 @@ let make_default_rhs ~loc = function
           | _ -> case)
         default_cases
     in
-    pexp_match ~loc [%expr _ppx_regexp_v] transformed
+    match transformed with
+    | [{ pc_lhs = { ppat_desc = Ppat_any; _ }; pc_guard = None; pc_rhs; _ }] ->
+        pc_rhs
+    | _ ->
+        pexp_match ~loc [%expr _ppx_regexp_v] transformed
 
 let transform_let ~mode ~ctx =
   let parser = match mode with `Pcre -> Regexp.parse_exn ~target:`Let | `Mik -> Regexp.parse_mik_exn ~target:`Let in
@@ -316,7 +320,7 @@ let transform_cases ~mode ~opts ~loc ~ctx cases =
             [%expr match [%e dispatchers] with Some result -> result | None -> [%e default_rhs]]
             handlers]]
   in
-  [%expr [%e match_expr]], [ re_binding ]
+  match_expr, re_binding
 
 (* processes each case individually instead of combining them into one RE *)
 let transform_mixed_match ~loc ~ctx ?matched_expr cases acc =