diff --git a/scheme/utils.scm b/scheme/utils.scm
index 6191278..e49b32d 100644
--- a/scheme/utils.scm
+++ b/scheme/utils.scm
@@ -1,12 +1,12 @@
 (define (display-to-string val)
   (let ((exp-port (open-output-string)))
-    (display exp exp-port)
+    (display val exp-port)
     (get-output-string exp-port)))
 
 ;;expression as string
-(define (write-to-string exp)
+(define (write-to-string val)
   (let ((exp-port (open-output-string)))
-    (write exp exp-port)
+    (write val exp-port)
     (get-output-string exp-port)))
 
 (define (on/off-option-processor name)