1 files changed, 11 insertions, 0 deletions
diff --git a/go/game/pos.go b/go/game/pos.go
index 133f599b..bf35ca3b 100644
--- a/go/game/pos.go
+++ b/go/game/pos.go
@@ -4,6 +4,12 @@ import (
 	"fmt"
 )
 
+// Position represents a zero-based position on the map.
+// TODO: Change to a 1-based coordinate system.
+//
+//	This allows to use the zero value as invalid Position.
+//
+// The origin is the upper left corner of the map.
 type Position struct {
 	X int
 	Y int
@@ -22,3 +28,8 @@ func (p Position) String() string {
 func INVALID_POSITION() Position {
 	return Position{-1, -1}
 }
+
+// Valid reports if a coordinate is smaller than 0.
+func (p Position) Valid() bool {
+	return p.X >= 0 && p.Y >= 0
+}