ローカル変数つき算術言語
code:language.ebnf
program = stmt*
stmt = expr ";"
expr = assign
assign = equality ("=" assign)?
equality = relational ("==" relational | "!=" relational)*
relational = add ("<" add | "<=" add | ">" add | ">=" add)*
add = mul ("+" mul | "-" mul)*
mul = unary ("*" unary | "/" unary)*
unary = ("+" | "-")? primary
primary = num | ident | "(" expr ")"