<program> := <statements> EOF <statements> := <statement> | <statement> SEP <statements> <statement> := let <id> = <expr> | <expr> <expr> := if <expr> then <statements> end | if <expr> then <statements> else <statements> end | while <expr> SEP <statements> end | <binexpr> | <number> | <id> <binexpr> :=