grammar.txt

<expr>          ::= <mlt_div_expr> <plus_minus> <expr> | <mlt_div_expr>
<mlt_div_expr>  ::= <atom> <mlt_div> <mlt_div_expr> | <atom>
<atom>          ::= <roman_numeral> | <minus_atom> | <brackets_atom>
<minus_atom>    ::= "-" <atom>
<brackets_atom> ::= "(" <atom> ")"

<plus_minus>    ::= "+" | "-"
<mlt_div>       ::= "*" | "/"

// Numerals Part
// Any number of "M" is allowed

<roman_numeral> ::= "Z" | <1000>
<1000>          ::= "M"  <1000> | <900> | "M"
<900>           ::= "CM" <500>  | <500> | "CM"
<500>           ::= "D"  <400>  | <400> | "D"
<400>           ::= "CD" <100>  | <100> | "CD"
<100>           ::= "CCC" <90>  | "CC" <90> | "C" <90> | <90> | "CCC" | "CC" | "C"
<90>            ::= "XC" <50>   | <50>  | "XC"
<50>            ::= "L"  <40>   | <40>  | "L"
<40>            ::= "XL" <10>   | <10>  | "XL"
<10>            ::= "XXX" <9>   | "XX" <9> | "X" <9> | <9> | "XXX" | "XX" | "X"
<9>             ::= "IX" <5>    | <5>   | "IX"
<5>             ::= "V"  <4>    | <4>   | "V"
<4>             ::= "IV" <1>    | <1>   | "IV"
<1>             ::= "I" | "II" | "III"