1 files changed, 15 insertions, 13 deletions
diff --git a/core.lisp b/core.lisp
index 43dd234..9fef78f 100644
--- a/core.lisp
+++ b/core.lisp
@@ -25,19 +25,21 @@
            (setf predicate
                  (normalize 'it predicate))))
         (t (error (format nil "Invalid predicate: ~a." predicate))))
-  `(the parser
-        (lambda (start input)
-          (declare (ignore start))
-          (if (has-data? input)
-            (let ((it (peek input)))
-              (if ,predicate
-                (make-parsing :tree it
-                              :start input
-                              :end (advance input))
-                (make-failure :place input
-                              :message (format nil "Expected: ~a, Got: ~:c." ',predicate it))))
-            (make-failure :place input
-                          :message (format nil "Reached end of input. Expected: ~a." ',predicate))))))
+  (let ((start (gensym))
+        (input (gensym)))
+    `(the parser
+          (lambda (,start ,input)
+            (declare (ignore ,start))
+            (if (has-data? ,input)
+              (let ((it (peek ,input)))
+                (if ,predicate
+                  (make-parsing :tree it
+                                :start ,input
+                                :end (advance ,input))
+                  (make-failure :place ,input
+                                :message (format nil "Expected: ~a, Got: ~:c." ',predicate it))))
+              (make-failure :place ,input
+                            :message (format nil "Reached end of input. Expected: ~a." ',predicate)))))))
 
 (declaim (ftype (function (parser parser &rest parser) parser) one-of))
 (defun one-of (first-parser second-parser &rest other-parsers)