diff --git a/src/doc/syntax.md b/src/doc/syntax.md
index 14005e0..78a0092 100644
--- a/src/doc/syntax.md
+++ b/src/doc/syntax.md
@@ -13,4 +13,12 @@ circle(A, len(AB))
 ## Primitives
 * `Point point(x, y)` is a 2D point. It returns an element of type `Point`
 * `Line line(Point from, Point to)` is a straight line. It returns an element of type `Line`.
-* `Circle circle(Point center, radius)` draws a circle at `center` and `radius`
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+* `Circle circle(Point center, radius)` draws a circle at `center` and `radius`
+
+## Grammar
+```
+instruction ::= identifier({parameter, })
+parameter ::= instruction | identifier | number
+identifier ::= (A-Za-z)
+number ::= (0-9)[.(0-9)]
+```
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