Big change: lexical scoping

This introduces lexical scoping of for clauses. See README.md

goof/iterators.scm

@@ -508,6 +508,21 @@
            ((var var))
            . rest))))
 
+
+;; this is an internal "accumulator". It is used for final tests
+;; :final in goof differs from in racket. It is lexical, meaning it
+;; is tested where it is placed in the clauses, and any subloop is
+;; executed completely.
+(define-syntax final
+  (syntax-rules (:acc)
+    ((_ :acc ((var) (test)) n . rest)
+     (n ()
+        ((final #f test))
+        (final)
+        ()
+        ()
+        . rest))))
+
 ;;; Here starts generator clauses.
 
 (define (generator->list gen)