diff --git a/grammar.txt b/grammar.txt
index 39f0c7a..6a6b9f4 100644
--- a/grammar.txt
+++ b/grammar.txt
@@ -7,8 +7,11 @@ shift          → andl ( ( "<<" | ">>" ) andl )*
 andl           → orl ( "&" orl )*
 orl            → andl ( ( "|" | "^" ) andl )*
 primary        → number
+	       → identifier
                | "(" expression ")"
 
+identifier → ( [a-z][A-Z][0-9][_] ) +
+
 number → "%" base2-number
        | "$" base16-number
        | "0b" base2-number