使用 ml-lex 构建词法分析器

发布于 2024-10-14 08:06:37 字数 410 浏览 5 评论 0原文

我需要创建一个与标准输入流绑定的 lexer 的新实例。
但是，当我输入时，

val lexer = makeLexer( fn n => inputLine( stdIn ) );

我收到一个我不明白的错误：（

stdIn:1.5-11.13 Error: operator and operand don't agree [tycon mismatch]
  operator domain: int -> string
  operand:         int -> string option
  in expression:

makeLexer 是我的源代码中存在的函数名称）

原文

I need to create a new instance of a lexer tied to the standard input stream.
However, when I type in

val lexer = makeLexer( fn n => inputLine( stdIn ) );

I get an error that I don't understand:

stdIn:1.5-11.13 Error: operator and operand don't agree [tycon mismatch]
  operator domain: int -> string
  operand:         int -> string option
  in expression:

(makeLexer is a function name present in my source code)

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黑寡妇 2024-10-21 08:06:37

inputLine 返回一个字符串选项< /code>，我的猜测是一个 string 是预期的。

您想要做的是让 makeLexer 采用 string 选项，如下所示：

fun makeLexer  NONE    = <whatever you want to do when stream is empty>
  | makeLexer (SOME s) = <the normal body makeLexer, working on the string s>

或将行更改为：

val lexer = makeLexer( fn n => valOf ( inputLine( stdIn ) ) );

valOf 采用选项类型并将其解包。

请注意，由于当流为空时 inputLine 返回 NONE，因此使用第一种方法可能比第二种方法更好。

inputLine returns a string option, and my guess is a string is expected.

What you want to do is either have makeLexer take a string option, like so:

fun makeLexer  NONE    = <whatever you want to do when stream is empty>
  | makeLexer (SOME s) = <the normal body makeLexer, working on the string s>

or change your line to:

val lexer = makeLexer( fn n => valOf ( inputLine( stdIn ) ) );

valOf takes an option type and unpacks it.

Note that, since inputLine returns NONE when the stream is empty, it's probably a better idea to use the first approach, rather than the second.

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用心笑 2024-10-21 08:06:37

用户指南的第 38 页（或论文中的第 32 页）给出了如何制作交互式流的示例ML-Lex 和 ML-Yacc

使用 inputLine 示例代码可以更简单。
因此，我将使用 Sebastian 给出的示例，请记住，如果用户按 CTRL-D，则 inputLine 可能至少使用 stdIn 返回 NONE 。

val lexer =
let 
  fun input f =
      case TextIO.inputLine f of
        SOME s => s
      | NONE => raise Fail "Implement proper error handling."
in 
  Mlex.makeLexer (fn (n:int) => input TextIO.stdIn)
end

此外，第 40 页（论文中为 34 页）的计算器示例显示了如何整体使用它。

一般来说，用户指南包含一些很好的示例和解释。

An example of how to make an interactive stream is given on page 38 (or 32 in the paper) of the User's Guide to ML-Lex and ML-Yacc

The example code could be simpler by using inputLine.
So I would use the example given by Sebastian, keeping in mind that inputLine might return NONE using stdIn atleast if the user presses CTRL-D.

val lexer =
let 
  fun input f =
      case TextIO.inputLine f of
        SOME s => s
      | NONE => raise Fail "Implement proper error handling."
in 
  Mlex.makeLexer (fn (n:int) => input TextIO.stdIn)
end

Also the calculator example on page 40 (34 in the paper) shows how to use this in a whole

In general the user guide contains some nice examples and explanations.

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