在许多不同的数据中重复某个功能 [英] Repeat a certain functionality in a lot of different datas

问题描述

我在Haskell编写了一个编译器，所以我们有一个很多 （或者至少对我来说看起来很像） data s和构造函数，如下所示：

I'm writing a compiler in Haskell, so we have a lot (or at least it seems like a lot for me) of datas and constructors, such as the followings:

data DataType
    = Int | Float | Bool | Char | Range | Type
    | String Width
    | Record (Lexeme Identifier) (Seq Field) Width
    | Union  (Lexeme Identifier) (Seq Field) Width
    | Array   (Lexeme DataType) (Lexeme Expression) Width
    | UserDef (Lexeme Identifier)
    | Void | TypeError  -- For compiler use


data Statement
    -- Language
    = StNoop
    | StAssign (Lexeme Access) (Lexeme Expression)
    -- Definitions
    | StDeclaration      (Lexeme Declaration)
    | StDeclarationList  (DeclarationList Expression)
    | StStructDefinition (Lexeme DataType)
    -- Functions
    | StReturn        (Lexeme Expression)
    | StFunctionDef   (Lexeme Declaration) (Seq (Lexeme DataType))
    | StFunctionImp   (Lexeme Identifier)  (Seq (Lexeme Identifier)) StBlock
    | StProcedureCall (Lexeme Identifier)  (Seq (Lexeme Expression))
    -- I/O
    | StRead  (Seq (Lexeme Access))
    | StPrint (Seq (Lexeme Expression))
    -- Conditional
    | StIf   (Lexeme Expression) StBlock StBlock
    | StCase (Lexeme Expression) (Seq (Lexeme When))      StBlock
    -- Loops
    | StLoop     StBlock (Lexeme Expression) StBlock
    | StFor      (Lexeme Identifier) (Lexeme Expression)  StBlock
    | StBreak
    | StContinue

还有更多。您可能已经注意到许多构造函数中的重复 Lexeme a 。

And many more. You may have noticed the repeating Lexeme a in many of the constructors.

Lexeme是以下 data

Lexeme is the following data

type Position = (Int, Int)

data Lexeme a = Lex
    { lexInfo :: a
    , lexPosn :: Position
    }

因此，它可以将元素的位置的信息保存在程序的文件中，用于报告错误和警告。

So it works for keeping the information of the Position of an element in the program's file, for reporting errors and warnings.

推荐答案

可以将 Lexeme 应用程序：

One could move "up" the Lexeme application:

type Access = Lexeme Access'
data Access' = ...
type Expression = Lexeme Expression'
data Expression' = ...
-- etc.
data Statement
    -- Language
    = StNoop
    | StAssign Access Expression
    -- Definitions
    | StDeclaration      Declaration
    | StDeclarationList  (DeclarationList Expression')  -- maybe you can also use Expression here?
    | StStructDefinition DataType
    ...

通过这种方式，您可以应用 Lexeme 每种类型定义一次，而不是每种类型使用。

In this way you apply Lexeme once every type definition, instead of once every type use.

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