light.ebnf

<program> ::= <expression>

<expression> ::= <atom>
             | '(' <function> <arguments> ')'

<function> ::= <atom>

<arguments> ::= <expression> <arguments>
             | ε  ; ε represents an empty string

<atom> ::= <variable>
        | <number>
        | <string>
        | <boolean>
        | <nil>

<variable> ::= <identifier>

<identifier> ::= <letter> <rest-of-identifier>

<rest-of-identifier> ::= <letter> <rest-of-identifier>
                    | <digit> <rest-of-identifier>
                    | ε

<number> ::= <integer>
         | <float>

<integer> ::= <digit> <digits>
           | '-' <digit> <digits>

<digits> ::= <digit> <digits>
         | ε

<digit> ::= '0' | '1' | '2' | ... | '9'

<float> ::= <integer> '.' <digits>

<string> ::= '"' <string-content> '"'

<string-content> ::= <char> <string-content>
                | ε

<char> ::= any valid character, excluding double quotes and control characters

<boolean> ::= 'true' | 'false'

<nil> ::= 'nil'