Add new ternary trees to store variables.

misc/custom.ml

@@ -135,11 +135,7 @@ module List(X : T) = struct
       | _ -> 1
 end
 
-
 module Pair(X : T)(Y : T) = struct
-  module Fst = X
-  module Snd = Y
-
   type t = X.t * Y.t
   let dump ppf (x,y) = Format.fprintf ppf "(%a,%a)" X.dump x Y.dump y
   let check (x,y) = X.check x; Y.check y
@@ -174,3 +170,21 @@ module Sum(X : T)(Y : T) = struct
     | Right t -> Format.fprintf ppf "R%a" Y.dump t
 end
 
+type 'a pairvar = Atm of 'a | Var of String.t
+
+module Var (X : T) = struct
+  type t = X.t pairvar
+  let hash = function Atm t -> X.hash t | Var s -> String.hash s
+  let check = function Atm t -> X.check t | Var _ -> ()
+  let compare t1 t2 =
+    match t1,t2 with
+    |Atm x, Atm y -> X.compare x y
+    |Var x, Var y -> String.compare x y
+    |Var _, Atm _ -> -1
+    |Atm _, Var _ -> 1
+
+  let equal t1 t2 = (compare t1 t2) = 0
+  let dump ppf = function 
+    |Atm x -> X.dump ppf x
+    |Var x -> String.dump ppf x
+end