Prevent infinite loop when invalid root note is provided.

1 files changed, 13 insertions, 2 deletions

diff --git a/scales/utils.scm b/scales/utils.scm
index 5c488a3..31d1c12 100644
--- a/scales/utils.scm
+++ b/scales/utils.scm
@@ -19,17 +19,28 @@
   #:use-module (srfi srfi-1)
   #:use-module (srfi srfi-9)
   #:use-module (srfi srfi-26)
-  #:export (all-notes-from
+  #:export (leave
+            all-notes-from
 
             make-scale-note
             scale-note-note
             scale-note-offset))
 
 
+(define (leave . messages)
+  (apply format (current-error-port) messages)
+  (exit 1))
+
+
+(define valid-notes
+  '(a ais b c cis d dis e f fis g gis))
+
 (define all-notes
-  (circular-list 'a 'ais 'b 'c 'cis 'd 'dis 'e 'f 'fis 'g 'gis))
+  (apply circular-list valid-notes))
 
 (define (all-notes-from root)
+  (when (not (member root valid-notes))
+    (leave "Invalid root note.  Valid notes are:\n\n~{  ~s\n~}\n" valid-notes))
   (find-tail (cut eqv? root <>) all-notes))