Lexer Grammar in EBNF

TokenList
       -> Token
       -> TokenList Token
Token
       -> Number     +> num
       -> Ident      +> ident
       -> Operator   +> oper
       -> Blank
$Digit -> "0123456789"
$Letter -> "ABCDEFGHIJKLMNOPQRSTUVWXYZ_abcdefghijklmnopqrstuvwxyz"
Space -> " \r\n"
$Ident
       -> Letter
       -> Ident Letter
       -> Ident Digit
$Number -> Digit... [ '.' Digit...]
$Operator -> '+' '-' '*' '/' '^' '<' '>' '<=' '>=' '==' '!='
Blank
       -> Space
       -> Blank Space