items		-> item* ;
item		-> align | type_decl | struct | messages | constant;

type_decl	-> "type" IDENT "=" type ";"
align		-> "align" "(" number ")" ";"
struct		-> "struct" IDENT "{" field ("," field)* ","? "}" ;
messages	-> "messages" IDENT "{" message* "}" ;
constant	-> "const" IDENT "=" number ";" ;

field		-> IDENT ":" type ;
number		-> NUMBER | IDENT ;
message		-> IDENT "{" field ("," field)* ","? "}" ;

type		-> IDENT | heap_array | field_array ;
heap_array	-> type "&" "[" "]" | type "[" "]" 
		 | type "&" "[" max_size | fixed_size "]" ;
field_array	-> type "[" max_size | fixed_size "]" ;
max_size	-> "^" number ;
fixed_size	-> number ;