abstract matchers and rules over fresh variable generator (#270)

lib/comby.mli

@@ -154,12 +154,16 @@ module Matchers : sig
 
         - [match_newline_toplevel] determines whether matching should terminate
           on newlines if a hole is not specified inside a recognized block syntax.
-          Default: [false]. *)
+          Default: [false].
+
+        - [fresh] is a generator for fresh values, used to evaluate equality
+          relations. *)
     val create
       :  ?disable_substring_matching:bool
       -> ?match_kind:match_kind
       -> ?significant_whitespace:bool
       -> ?match_newline_toplevel:bool
+      -> ?fresh:(unit -> string)
       -> unit
       -> t
   end
@@ -461,12 +465,15 @@ module Rule : sig
   (** [create] parses and creates a rule. *)
   val create : string -> t Or_error.t
 
-  (** [apply matcher substitute_in_place rule env] applies a [rule] according to
-      some [matcher] for existing matches in [env]. If [substitute_in_place] is
-      true, rewrite rules substitute their values in place (default true). *)
+  (** [apply matcher substitute_in_place fresh rule env] applies a [rule]
+      according to some [matcher] for existing matches in [env]. If
+      [substitute_in_place] is true, rewrite rules substitute their values in
+      place (default true). [fresh] introduces fresh variables for evaluating
+      rules. *)
   val apply
     :  ?matcher:(module Matchers.Matcher.S)
     -> ?substitute_in_place:bool
+    -> ?fresh:(unit -> string)
     -> t
     -> Match.environment
     -> result

lib/language/alpha_rule.ml

@@ -39,9 +39,16 @@ let merge_match_environments matches environment' =
 type rewrite_context =
   { variable : string }
 
+let counter =
+  let uuid_for_id_counter = ref 0 in
+  fun () ->
+    uuid_for_id_counter := !uuid_for_id_counter + 1;
+    Format.sprintf "gu3ssme_%012d" !uuid_for_id_counter
+
 let rec apply
     ?(matcher = (module Matchers.Alpha.Generic : Matchers.Matcher.S))
     ?(substitute_in_place = true)
+    ?(fresh = counter)
     predicates
     env =
   let open Option in
@@ -104,7 +111,7 @@ let rec apply
       Option.value_map result ~f:ident ~default:(false, Some env)
     | Match (String template, cases) ->
       let source, _ = Rewriter.Rewrite_template.substitute template env in
-      let fresh_var = Uuid_unix.(Fn.compose Uuid.to_string create ()) in
+      let fresh_var = fresh () in
       let env = Environment.add env fresh_var source in
       rule_match env (Match (Variable fresh_var, cases))
     | RewriteTemplate rewrite_template ->

lib/language/omega_rule.ml

@@ -41,9 +41,16 @@ let merge_match_environments matches environment' =
 type rewrite_context =
   { variable : string }
 
+let counter =
+  let uuid_for_id_counter = ref 0 in
+  fun () ->
+    uuid_for_id_counter := !uuid_for_id_counter + 1;
+    Format.sprintf "gu3ssme_%012d" !uuid_for_id_counter
+
 let rec apply
     ?(matcher = (module Matchers.Omega.Generic : Matchers.Matcher.S))
     ?(substitute_in_place = true)
+    ?(fresh = counter)
     predicates
     env =
   let open Option in
@@ -106,7 +113,7 @@ let rec apply
       Option.value_map result ~f:ident ~default:(false, Some env)
     | Match (String template, cases) ->
       let source, _ = Rewriter.Rewrite_template.substitute template env in
-      let fresh_var = Uuid_unix.(Fn.compose Uuid.to_string create ()) in
+      let fresh_var = fresh () in
       let env = Environment.add env fresh_var source in
       rule_match env (Match (Variable fresh_var, cases))
     | RewriteTemplate rewrite_template ->

lib/language/types.ml

@@ -21,6 +21,7 @@ module type Engine = sig
   val apply
     :  ?matcher:(module Matcher.S)
     -> ?substitute_in_place:bool
+    -> ?fresh:(unit -> string)
     -> t
     -> environment
     -> result

lib/matchers/alpha.ml

@@ -370,7 +370,7 @@ module Make (Language : Language.S) (Metasyntax : Metasyntax.S) = struct
          let environment =
            if Environment.exists environment identifier && String.(identifier <> "_") then
              let fresh_hole_id =
-               Format.sprintf "%s_%s_equal" Uuid_unix.(Fn.compose Uuid.to_string create ()) identifier
+               Format.sprintf "%s_%s_equal" (!configuration_ref.fresh ()) identifier
              in
              Environment.add ~range environment fresh_hole_id (String.concat matched)
            else

lib/matchers/configuration.ml

@@ -7,16 +7,25 @@ type t =
   ; significant_whitespace : bool
   ; disable_substring_matching : bool
   ; match_newline_toplevel : bool
+  ; fresh : unit -> string
   }
 
+let counter =
+  let uuid_for_id_counter = ref 0 in
+  fun () ->
+    uuid_for_id_counter := !uuid_for_id_counter + 1;
+    Format.sprintf "!@#$%012d" !uuid_for_id_counter
+
 let create
     ?(disable_substring_matching = false)
     ?(match_kind = Fuzzy)
     ?(significant_whitespace = false)
     ?(match_newline_toplevel = true)
+    ?(fresh = counter)
     () =
   { match_kind
   ; significant_whitespace
   ; disable_substring_matching
   ; match_newline_toplevel
+  ; fresh
   }

lib/matchers/configuration.mli

@@ -7,6 +7,7 @@ type t =
   ; significant_whitespace : bool
   ; disable_substring_matching : bool
   ; match_newline_toplevel : bool
+  ; fresh : unit -> string
   }
 
 val create
@@ -14,5 +15,6 @@ val create
   -> ?match_kind:match_kind
   -> ?significant_whitespace:bool
   -> ?match_newline_toplevel:bool
+  -> ?fresh:(unit -> string)
   -> unit
   -> t

lib/matchers/omega.ml

@@ -95,7 +95,7 @@ let record_match_context pos_before pos_after =
   if rewrite then Buffer.add_string actual result;
   matches_ref := match_context :: !matches_ref
 
-module Make (Language : Language.S) (_ : Metasyntax.S) = struct
+module Make (Language : Language.S) (Unimplemented : Metasyntax.S) = struct
   include Language.Info
   module Syntax = Language.Syntax
 
@@ -133,11 +133,10 @@ module Make (Language : Language.S) (_ : Metasyntax.S) = struct
       let range = { match_start = before; match_end = after } in
       let add identifier = Environment.add ~range !current_environment_ref identifier content in
       let environment =
-        match Environment.exists !current_environment_ref identifier with
+        match Environment.exists !current_environment_ref identifier && String.(identifier <> "_") with
         | true ->
-          (* FIXME: get rid of UUID *)
           let fresh_hole_id =
-            Format.sprintf "%s_%s_equal" Uuid_unix.(Fn.compose Uuid.to_string create ()) identifier
+            Format.sprintf "%s_%s_equal" (!configuration_ref.fresh ()) identifier
           in
           add fresh_hole_id
         | false -> add identifier

lib/pipeline/pipeline.ml

@@ -37,7 +37,8 @@ let apply_rule ?(substitute_in_place = true) matcher omega rule matches =
         else
           Rule.Alpha.apply
       in
-      let sat, env = apply ~substitute_in_place ~matcher rule environment in
+      let fresh () = Uuid_unix.(Fn.compose Uuid.to_string create ()) in
+      let sat, env = apply ~fresh ~substitute_in_place ~matcher rule environment in
       (if sat then env else None)
       >>| fun environment -> { matched with environment })
 
@@ -282,20 +283,21 @@ let run
     ; metasyntax
     }
   =
+  let fresh = match compute_mode with
+    | `Sequential -> None
+    | _ -> Some (fun () -> Uuid_unix.(Fn.compose Uuid.to_string create ()))
+  in
+
   let match_configuration =
     Matchers.Configuration.create
       ~disable_substring_matching
       ~match_kind:Fuzzy
       ~match_newline_toplevel
+      ?fresh
       ()
   in
   let start_time = Statistics.Time.start () in
 
-  let fresh = match compute_mode with
-    | `Sequential -> None
-    | _ -> Some (fun () -> Uuid_unix.(Fn.compose Uuid.to_string create ()))
-  in
-
   let per_unit ~(input : single_source) ~output_path =
     run_on_specifications
       specifications

lib/rewriter/rewrite.ml

@@ -7,7 +7,6 @@ let debug =
   Sys.getenv "DEBUG_COMBY"
   |> Option.is_some
 
-
 let substitute_match_contexts ?fresh ?metasyntax (matches: Match.t list) source replacements =
   if debug then Format.printf "Matches: %d | Replacements: %d@." (List.length matches) (List.length replacements);
   let rewrite_template, environment =