commit it tidied up version of the patch to fix bug 497, with a consistent error message (none of the others include the Error. prefix) and some documentation of what the nyx function returns for future sanity.

lib-src/libnyquist/nyx.c

@@ -875,7 +875,11 @@ int nyx_get_audio_num_channels()
    }
 
    if (vectorp(nyx_result)) {
-      return getsize(nyx_result);
+      if (getsize(nyx_result) == 1) {
+        return -1; // invalid number of channels in array
+      } else {
+        return getsize(nyx_result);
+      }
    }
 
    return 1;

lib-src/libnyquist/nyx.h

@@ -64,6 +64,12 @@ extern "C"
    
    nyx_rval    nyx_eval_expression(const char *expr);
    
+   /** @brief Get the number of channels in the Nyquist audio object
+    *
+    * @return The positive integer number of audio channels in the
+    * Nyquist audio object, 0 if not an audio object, -1 one if
+    * Nyquist returns an array of samples (which we can't handle)
+    */
    int         nyx_get_audio_num_channels();
    int         nyx_get_audio(nyx_audio_callback callback,
                              void *userdata);

src/effects/nyquist/Nyquist.cpp

@@ -917,6 +917,13 @@ bool EffectNyquist::ProcessOne()
       return false;
    }
 
+   if (outChannels == -1) {
+      wxMessageBox(_("Nyquist returned one audio channel as an array.\n"),
+                   wxT("Nyquist"),
+                   wxOK | wxCENTRE, mParent);
+      return false;
+   }
+
    double rate = mCurTrack[0]->GetRate();
    for (i = 0; i < outChannels; i++) {
       sampleFormat format = mCurTrack[i]->GetSampleFormat();