more doc comments

src_plugins/show/ppx_deriving_show.ml

@@ -49,6 +49,15 @@ let fresh_type_maker type_decl =
     bound := newvar :: !bound;
     Typ.var newvar
 
+(** [pp_type_of_decl decl] returns type for [pp_xxx] where xxx is the type name. 
+    For example, for [type ('a, 'b) map] it produces 
+    [(formatter -> 'a -> unit) -> (formatter -> 'b -> unit) -> formatter -> ('a, 'b) map -> unit].
+    For GADTs, the optional parameter [refined_param_pos] specifies the index of refined 
+    parameters i.e., [0] for ['a] in [type ('a, 'b) map] and [1] for ['b].
+    If present, the type parameter is rendered as any [type _] type, to mark the type parameter is 
+    actually ignored. For example, for [type ('a, 'b) map] with [refined_param_pos=[1]], it produces
+    [(formatter -> 'a -> unit) -> (formatter -> _ -> unit) -> formatter -> ('a, 'b) map -> unit]
+    (see [_] instead of ['b] in the type for the second argument). *)
 let pp_type_of_decl ?(refined_param_pos=[]) type_decl =
   let loc = type_decl.ptype_loc in
   let typ = Ppx_deriving.core_type_of_type_decl type_decl in
@@ -60,6 +69,8 @@ let pp_type_of_decl ?(refined_param_pos=[]) type_decl =
     type_decl
     [%type: Ppx_deriving_runtime.Format.formatter -> [%t typ] -> Ppx_deriving_runtime.unit]
 
+(** Same as [pp_type_of_decl] but type parameters are rendered as locally abstract types rather than
+    type variables. *)
 let pp_type_of_decl_newtype ?(refined_param_pos=[]) type_decl =
   let loc = type_decl.ptype_loc in
   let typ = Ppx_deriving.core_type_of_type_decl_with_newtype type_decl in
@@ -70,6 +81,8 @@ let pp_type_of_decl_newtype ?(refined_param_pos=[]) type_decl =
     type_decl
     [%type: Ppx_deriving_runtime.Format.formatter -> [%t typ] -> Ppx_deriving_runtime.unit]
 
+(** [show_type_of_decl decl] returns type for [show_xxx] where xxx is the type name. 
+    The optional parameter [refined_param_pos] behaves same as [pp_type_of_decl]. *)
 let show_type_of_decl ?(refined_param_pos=[]) type_decl =
   let loc = type_decl.ptype_loc in
   let typ = Ppx_deriving.core_type_of_type_decl type_decl in