start -> stmt [SimNode]
  stmt -> if-stmt [SimNode]
    if-stmt -> IF expr THEN stmt [SimNode]
      IF
      expr -> NUMBER [SimNode]
        NUMBER
      THEN
      stmt -> if-stmt [SimNode]
        if-stmt -> IF expr THEN stmt ELSE >! stmt [SimNode]
          IF
          expr -> NUMBER [SimNode]
            NUMBER
          THEN
          stmt -> expr-stmt [SimNode]
            expr-stmt -> expr [SimNode]
              expr -> NUMBER [SimNode]
                NUMBER
          ELSE
          stmt -> expr-stmt [SimNode]
            expr-stmt -> expr [SimNode]
              expr -> NUMBER [SimNode]
                NUMBER