Changed [lookup] to take [env] first.

src/BindingFormsUnbound.ml

@@ -26,7 +26,8 @@
    The combinator [inner(p)] can be viewed as sugar for [rebind(outer(p))].
 
    Our [rebind(p)] takes just one argument. Weirich et al.'s [rebind],
-   which takes two arguments, is emulated by writing [p1 * rebind(p2)]. *)
+   which takes two arguments, is emulated by writing [p1 * rebind(p2)].
+   This encoding relies on the fact that pairs are traversed left-to-right. *)
 
 (* -------------------------------------------------------------------------- *)
 
@@ -155,7 +156,7 @@ let check_recursive_permitted (penv : 'env penv) : unit =
 class virtual ['self] map = object (self : 'self)
 
   method private virtual extend: 'bn1 -> 'env -> 'bn2 * 'env
-  method private virtual lookup: 'bn1 -> 'env -> 'bn2
+  method private virtual lookup: 'env -> 'bn1 -> 'bn2
 
   (* [visit_abstraction] initializes an enriched environment using the
      auxiliary function [abstraction]. *)
@@ -182,7 +183,7 @@ class virtual ['self] map = object (self : 'self)
           penv.current := env;
           x2
       | Lookup ->
-          self#lookup x1 env
+          self#lookup env x1
 
   (* [inner(p)] can be viewed as sugar for [rebind(outer(p))]. Therefore, this
      code should ideally be generated. *)