/* token is first stage of parsing */
token             ::= insert
                    | select
                    | meta-command
                    | int
                    | string
                    | semicolon
                    | end-of-file

/* command is second stage of parsing */
command           ::= cmd-insert semicolon
                    | cmd-select semicolon
cmd-insert        ::= insert int string string
cmd-select        ::= select

insert            ::= "insert"
select            ::= "select"
semicolon         ::= ";"

meta-command      ::= meta-command-verb end-of-file
meta-command-verb ::= ".exit"
                    | ".about"
                    | ".version"

int               ::= sign? digit+
sign              ::= "+"
                    | "-"
digit             ::= "0"
                    | "1"
                    | "2"
                    | "3"
                    | "4"
                    | "5"
                    | "6"
                    | "7"
                    | "8"
                    | "9"

string            ::= '"' string-char* '"'
string-char       ::= '\' utf8-char
                    | utf8-char-not-dbl-quote