From 18843938965b101d4cb49d3bbe23760b14000254 Mon Sep 17 00:00:00 2001
From: rekado <rekado@elephly.net>
Date: Sat, 1 Oct 2016 18:33:49 +0200
Subject: Validate scales.

---
 scales/scales.scm | 15 +++++++++++++++
 scales/ui.scm     | 16 ++++++++++++----
 2 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/scales/scales.scm b/scales/scales.scm
index 4d80bbf..38c7579 100644
--- a/scales/scales.scm
+++ b/scales/scales.scm
@@ -19,6 +19,7 @@
   #:use-module (srfi srfi-1)
   #:use-module (scales utils)
   #:export (steps->scale
+            valid-scales
 
             lydian
             ionian
@@ -76,3 +77,17 @@ root note and returns a list of scale notes."
   (steps->scale '(2 2 2 2 2 2)))
 (define chromatic
   (steps->scale '(1 1 1 1 1 1 1 1 1 1 1)))
+
+(define valid-scales
+  '(lydian
+    ionian
+    mixolydian
+    lydian-b7
+    altered
+    symmetrical-diminished
+    dorian
+    aeolian
+    phrygian
+    locrian
+    whole-tone
+    chromatic))
diff --git a/scales/ui.scm b/scales/ui.scm
index b95d5d9..8ddfda6 100644
--- a/scales/ui.scm
+++ b/scales/ui.scm
@@ -17,6 +17,7 @@
 
 (define-module (scales ui)
   #:use-module (ice-9 getopt-long)
+  #:use-module (scales utils)
   #:use-module (scales fretboard)
   #:use-module (scales scales)
   #:export (main))
@@ -29,10 +30,17 @@
     (lambda _ tuning)))
 
 (define (lookup-scale scale)
-  (catch #t
-    (lambda _
-      (module-ref (resolve-interface '(scales scales)) scale))
-    (lambda _ (steps->scale scale))))
+  (if (member scale valid-scales)
+      (module-ref (resolve-interface '(scales scales)) scale)
+      (if (not (pair? scale))
+          (leave "
+Invalid scale \"~s\".
+The scale must be either the name of a pre-defined scale or a list of steps.
+
+Valid scale names are:
+
+~{  ~s \n~}\n" scale valid-scales)
+          (steps->scale scale))))
 
 (define (main args)
   (let* ((option-spec '((version (single-char #\v) (value #f))
-- 
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