Haskell - 如何最好地表示一个编程语言的语法？ [英] Haskell - How to best to represent a programming language's grammar?

问题描述

我一直在寻找Haskell，我很想写一个编译器（作为一个学习练习），因为它的许多内在的功能可以很容易地应用于编译器（特别是递归的良好的编译器） 。

我无法完全理解的是如何用Haskell-ian方式表示语言的语法。我的第一个想法是使用递归数据类型定义，但我不能看到我如何使用它们来匹配语言中的关键字（if）。

想法和建议非常感谢，

Pete

解决方案

数据类型就可以了。例如，给定语言：

  expr :: = var 
 | true
 | false
 | ifexprthenexprelseexpr 
 | （expr）
  

此语言的示例表达式为：

  if true then x else（if false then y else true）
  

您的Haskell数据类型如下所示：

  data Expr = Var String 
 | Lit Bool 
 |如果Expr Expr Expr 
  

您的解析器会小心翻译，例如 x into Varx和 true into 等。Ie：

  parseif x then false else true
 = = If（Varx）（Lit False）（Lit True）
  

使用Norman的回答中提到的技术，或使用 Parsec 或使用解析器生成器，如快乐。

I've been looking at Haskell and I'd quite like to write a compiler (as a learning exercise) in it, since a lot of it's innate features can be readily applied to a compiler (particularly a recursive decent compiler).

What I can't quite get my head around is how to represent a language's grammar in a Haskell-ian way. My first thought was to use recursive data type definitions, but I can't see how I use them to match against keywords in the language ("if") for example.

Thoughts and suggestions greatly appreciated,

Pete

解决方案

A recursive data type is fine for this. For example, given the language:

expr ::= var
      |  "true"
      |  "false"
      |  "if" expr "then" expr "else" expr
      |  "(" expr ")"

an example expression in this language would be:

if true then x else (if false then y else true)

Your Haskell data type would look something like this:

data Expr = Var String
          | Lit Bool
          | If Expr Expr Expr

Your parser then takes care to translate, e.g., x into Var "x", and true into Lit True, etc. I.e.:

parse "if x then false else true" 
  ==  If (Var "x") (Lit False) (Lit True)

For writing parsers you can roll your own using the techniques mentioned in Norman's answer, or using Parsec or use parser generators like Happy.

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