Add .mli for SAST pretty printer with minimal comments

src/stages/ast_simplified/PP.mli

@@ -0,0 +1,33 @@
+(** Pretty printer for the Simplified Abstract Syntax Tree *)
+
+open Types
+
+val type_expression : Format.formatter -> type_expression -> unit
+
+val literal : Format.formatter -> literal -> unit
+
+val expression : Format.formatter -> expression -> unit
+
+val option_type_name : Format.formatter -> string * type_expression option -> unit
+
+val assoc_expression : Format.formatter -> (expr * expr) -> unit 
+
+val access : Format.formatter -> access -> unit
+
+val access_path : Format.formatter -> access_path -> unit
+
+val type_annotation : Format.formatter -> type_expression option -> unit
+
+val single_record_patch : Format.formatter -> string * expr -> unit
+
+val single_tuple_patch : Format.formatter -> int * expr -> unit
+
+(* Shows the type expected for the matched value *)
+val matching_type : Format.formatter -> 'a matching -> unit
+
+val matching_variant_case_type : Format.formatter -> (string * string) * 'a -> unit
+
+val declaration : Format.formatter -> declaration -> unit
+
+(** Pretty print a full program AST *)
+val program : Format.formatter -> program -> unit