1 files changed, 23 insertions, 0 deletions
diff --git a/dir.go b/dir.go
new file mode 100644
index 0000000..693db98
--- /dev/null
+++ b/dir.go
@@ -0,0 +1,23 @@
+package mt
+
+// A Dir represents a direction parallel to an axis.
+type Dir uint8
+
+const (
+	East  Dir = iota // +X
+	Above            // +Y
+	North            // +Z
+	South            // -Z
+	Below            // -Y
+	West             // -X
+	NoDir
+)
+
+// Opposite returns the Dir's opposite.
+// NoDir is its own opposite.
+func (d Dir) Opposite() Dir {
+	if d >= NoDir {
+		return NoDir
+	}
+	return 5 - d
+}