refactor exceptions to be less verbose

1 files changed, 13 insertions, 11 deletions

diff --git a/mcgoron.iterator.string.scm b/mcgoron.iterator.string.scm
index 62cb960..762b79d 100644
--- a/mcgoron.iterator.string.scm
+++ b/mcgoron.iterator.string.scm
@@ -16,18 +16,15 @@
 (define (string-cursor-valid-movement? str cursor spaces)
   ;; Return #T if moving CURSOR forwards or backwards SPACES is well
   ;; defined.
-  ;; 
-  ;; Will return an error if SPACES is not an integer.
   (cond
-    ((not (integer? spaces))
-     (raise (non-integer-movement-exception spaces)))
+    ((zero? spaces) #t)
     ((negative? spaces)
      (<= (- spaces)
          (string-cursor-diff str (string-cursor-start str) cursor)))
     ((positive? spaces)
      (<= spaces
          (string-cursor-diff str cursor (string-cursor-end str))))
-    (else #t)))
+    (else #f)))
 
 (define-invocation string-iterator-str)
 (define-invocation string-iterator->cursor)
@@ -42,18 +39,23 @@
      (string-cursor-back str cursor (- spaces)))
     (else (string-cursor-forward str cursor spaces))))
 
-(define-iterator-implementation (string-iterator str cursor)
+(define-iterator-implementation (string-iterator str cursor) self
   ((iterator-at-start?)
    (string-cursor=? (string-cursor-start str) cursor))
   ((iterator-at-end?)
    (string-cursor=? (string-cursor-end str) cursor))
   ((iterator-advance spaces)
-   (if (string-cursor-valid-movement? str cursor spaces)
-       (let ((cursor (string-cursor-advance str cursor spaces)))
-         (string-iterator str cursor))
-       #f))
+   (cond
+     ((not (integer? spaces))
+      (raise (non-integer-movement-exception self spaces)))
+     ((string-cursor-valid-movement? str cursor spaces)
+      (let ((cursor (string-cursor-advance str cursor spaces)))
+        (string-iterator str cursor)))
+     (else #f)))
   ((iterator-ref)
-   (string-ref/cursor str cursor))
+   (if (iterator-at-end? self)
+       (raise (ref-at-end-exception self))
+       (string-ref/cursor str cursor)))
   ((iterator->index)
    (string-cursor->index str cursor))
   ((string-iterator-str) str)