Got the scanner running again. Seems to be picking up punctuation, labels, identifiers and strings as expected.

src/opcodes.c

@@ -156,9 +156,30 @@ int IsRegister(const char* text, Registers* reg) {
     if (!text) return 0;
 
     int length = strlen(text);
+    Registers r = R8;
 
     if (length != 2) return 0;
     if (text[0] != 'r') return 0;
 
-    return text[1] >= '1' && text[1] <= '8';
+    switch(text[1]) {
+        case '1':
+            r--;
+        case '2':
+            r--;
+        case '3':
+            r--;
+        case '4':
+            r--;
+        case '5':
+            r--;
+        case '6':
+            r--;
+        case '7':
+            r--;
+        case '8':
+            if (reg) *reg = r;
+            return 1;
+        default:
+            return 0;
+    }
 }