I've written an LALR1 parser which seems to work. It can be parameterised for the type of symbols it receives. The only binding is Eq.

我已经编写了一个LALR1解析器，该解析器似乎可以工作。它可以根据它接收到的符号类型进行参数化。唯一的结合是等式。

module LALR.Parser where

data Rule symbolT = Rule 
    {
        lhs :: symbolT,
        rhs :: Int
    }

data Action symbolT = Accept
    | Goto (State symbolT)
    | Shift (State symbolT)
    | Reduce (Rule symbolT)

data State symbolT = State
    {
        transitions :: [ (symbolT, Action symbolT) ]
    }

data Parser symbolT = Parser
    {
        states :: [State symbolT],
        input  :: [symbolT]
    }

data Result symbolT = UnexpectedSymbol symbolT
    | Accepted
    | Pending (Parser symbolT)
    | EmptyInput
    | EmptyStack

build :: State symbolT -> [symbolT] -> Parser symbolT
build state input = Parser
    {
        states = [state],
        input = input
    }

step :: Eq symbolT => Parser symbolT -> Result symbolT
step (Parser [] _) = EmptyStack
step (Parser _ []) = EmptyInput
step parser@(Parser states@(state : statesTail) input@(lookAhead : inputTail) ) = case (action) of
    Nothing                            -> UnexpectedSymbol lookAhead
    Just Accept                        -> Accepted
    Just (Shift target)                -> Pending (Parser (target : states) inputTail)
    Just (Reduce rule@(Rule lhs rhs) ) -> Pending (Parser (drop rhs states) (lhs : input) )
    Just (Goto target)                 -> Pending (Parser (target : states) inputTail )
    where
        action = lookup lookAhead (transitions state)

run :: Eq symbolT => Parser symbolT -> Result symbolT
run parser = case (step parser) of
    Pending parser -> run parser
    result         -> result

However, now I want to transform this parser into a compiler, which not only accepts or rejects a given input, but actually converts it into something useful. Basically, I am thinking to add a handler which can handle the different actions taken. Now my question is the following:

然而，现在我想将这个解析器转换为编译器，它不仅接受或拒绝给定的输入，而且实际上将其转换为有用的东西。基本上，我正在考虑添加一个处理程序，可以处理采取的不同行动。现在我的问题是：

The compiler will require not only to receive mere Symbols, but Symbols with bells and whistles, e.g. a payload (whatever the lexer lexed), or a line number, a file name, or something else.

编译器不仅需要接收简单的符号，还需要接收带有花哨的符号，例如有效负载(无论Lexer词法是什么)、行号、文件名或其他东西。

In an object oriented language I would recur to inheritance and derive a class from Symbol. But what is the way to go in Haskell?

在面向对象的语言中，我会求助于继承并从符号派生一个类。但在哈斯克尔，该怎么走呢？

Should I define a class Token which requires a function symbol :: Token -> Symbol and then I would create some data structure that instances that class? Changing the bindings from Eq symbolT to Token symbolT and then calling symbol when I need to lookup the symbol?

我应该定义一个类Token，它需要一个函数symbol：：Token -> Symbol，然后我会创建一些数据结构来实例化这个类吗？将绑定从Eq symbolT更改为Token symbolT，然后在需要查找symbol时调用symbol？

(I am trying to study the language limiting myself mostly to the Prelude.)

(我正在努力学习这门语言，把自己主要局限于前奏曲。)

UPDATE:

最新情况：

Your entire code is parameterised by symbolT. Why just not assume that symbolT is a symbol with a payload? Do you want different types of payload for different symbols?

Yes, I want different payloads. The Lexer produces a [Token].

是的，我想要不同的有效载荷。词法分析器生成一个[标记]。

data Token = Assignment | Name String | Number Int

lex :: String -> Maybe [Token]

I could derive Eq so that it ignores the payload, e.g.

我可以推导出等式，这样它就忽略了有效载荷，例如

instance Eq Token where
    (==) (Name _) (Name _) = True
    -- etc

but then in the definition of the transitions of the states I would need to give it a dummy token e.g. [ (Number 0, Accept), (Name "", Shift state3) ] which looks kind of wrong.

但是，在状态转换的定义中，我需要给它一个虚拟标记，例如[(数字0，接受)，(名称“”，移位状态3)]，这看起来有点错误。

I was thinking about something like:

我在想一些类似的事情：

class Tkn a symbolT where
    symbol :: a -> symbolT

and then when I lookup the transitions, I would call that method to extract the symbol.

然后，当我查找转换时，我会调用该方法来提取符号。

I am not sure if I am explaining myself or if any of this makes any sense.

我不确定我是否在解释自己，或者这一切是否有任何意义。