Nand To Tetris (Jack)：简单，如果条件相等测试给出这个错误- "Expected or ~ or ( in Term)“

Question

class Main {
  function void main() {
    var String foo;
    let foo = "bar";

    if (foo == "bar") {
      do Output.printString("true");
    }
    else {
      do Output.printString("false");
    }

    return;
  }
}

我得到的错误是：Expected - or ~ or ( in term。

完整输出：

code/nand2tetris » tools/JackCompiler.sh projects/09/Test
Compiling /Users/adamzerner/code/nand2tetris/projects/09/Test
In Main.jack (line 6): In subroutine main: Expected - or ~ or ( in term
code/nand2tetris »

这个错误是什么意思？