diff --git a/src/doc/syntax.md b/src/doc/syntax.md
index 78a0092..c01cdf1 100644
--- a/src/doc/syntax.md
+++ b/src/doc/syntax.md
@@ -17,7 +17,7 @@ circle(A, len(AB))
 
 ## Grammar
 ```
-instruction ::= identifier({parameter, })
+instruction ::= identifier({parameter, }) [-> identifer]
 parameter ::= instruction | identifier | number
 identifier ::= (A-Za-z)
 number ::= (0-9)[.(0-9)]