Define [fa] using [iter] instead of [reduce].

src/AlphaLibMacros.cppo.ml

@@ -7,6 +7,8 @@
 
 (* -------------------------------------------------------------------------- *)
 
+(* [fa] could be defined in terms of [reduce], as follows. *)
+
 #define FA_CLASS     __fa
 #define FA_FUN(term) CONCAT(fa_, term)
 
@@ -20,6 +22,26 @@
   let FA_FUN(term) t =                                                         \
     new FA_CLASS # VISIT(term) () t                                            \
 
+#undef __FA
+#undef FA
+
+(* -------------------------------------------------------------------------- *)
+
+(* We prefer to define [fa] in terms of [iter] because we wish to eliminate
+   our dependency on [reduce] visitors. *)
+
+#define __FA                                                                   \
+  class FA_CLASS = object                                                      \
+    inherit [_] iter                                                           \
+    inherit [_] KitFa.iter                                                     \
+  end                                                                          \
+
+#define FA(term)                                                               \
+  let FA_FUN(term) t =                                                         \
+    let o = new FA_CLASS in                                                    \
+    o # VISIT(term) KitFa.empty t;                                             \
+    o # accu
+
 (* -------------------------------------------------------------------------- *)
 
 #define FILTER_CLASS     __filter