program : [[statement | expression] Delimiter ? ]*;
statement : [declaration | definition];
declaration : Extern prototype;
definition : Def prototype expression;
prototype : Ident OpeningParenthesis [Ident Comma ?]* ClosingParenthesis;
expression : [binary_expr | unary_expr];
binary_expr : [unary_expr (Op unary_expr)* ];
unary_expr : [( "!" | "-")? primary_expr];
primary_expr : [Ident | Number | call_expr | parenthesis_expr];
call_expr : Ident OpeningParenthesis [expression Comma ?]* ClosingParenthesis;
parenthesis_expr : OpeningParenthesis expression ClosingParenthesis;
