Data update

Task/ISBN13-check-digit/SETL/isbn13-check-digit.setl

@@ -0,0 +1,22 @@
+program isbn13;
+    loop for test in [
+        "978-0596528126", "978-0596528120",
+        "978-1788399081", "978-1788399083"
+    ] do
+        print(test + if valid_isbn13 test then ": good" else ": bad" end);
+    end loop;
+
+    op valid_isbn13(isbn);
+        if #isbn /= 14
+           or isbn(4) /= '-'
+           or exists c in isbn | not c in "0123456789-" then
+            return false;
+        end if;
+
+        m := 3;
+        loop for ch in isbn | ch in "0123456789" do
+            s +:= val ch * (m := 4 - m);
+        end loop;
+        return s mod 10 = 0;
+    end op;
+end program;