IS -> "::="
OR -> "|"
OB -> "("
CB -> ")"
OS -> "["
CS -> "]"
OC -> "{"
CC -> "}"
##
IDENT -> ([a-z]|[A-Z])([a-z]|([A-Z]|[0-9]))* 
STR -> \" ([a-z]|([A-Z]|[0-9]))* \"
NL -> \n
##
##
EOL -> \r
SPACE -> \s|\t
##
start -> rule <NL> start
start -> EMPTY
rule -> <IDENT>  <IS> expression
expression -> term
expression -> term <OR> expression
term -> factor term
term -> factor 
factor -> <IDENT>
factor ->  <STR> 
factor -> <OB>  expression  <CB>
factor -> <OS>  expression  <CS>
factor -> <OC>  expression  <CC>