如何在 Nim 中为 kind 变体编写辅助符

问题描述

尝试编写访问器以获取具有 kind 成员的对象的值，我在宏中收到无效的缩进错误，我不知道为什么

我想我可能会错误地构建宏，但如果有更好的方法来抽象对象中的类型，那就太好了。

这是我正在工作的实现：

import macros,strutils,tables

type Types = enum Integer,Float,String,Array
type StyleName = enum X,Y,W,H,Left,Margin,Padding,Color,BorderColor

type Value=object
  case kind : Types
  of Integer: ival:int
  of Float: fval:float
  of String: sval:string
  of Array: cval:array[4,int]
proc tovalue(x:float):Value=Value(kind:Float,fval:x)
proc tovalue(x:int):Value=Value(kind:Integer,ival:x)
proc tovalue(x:string):Value=Value(kind:String,sval:x)
proc tovalue(x:array[4,int]):Value=Value(kind:Array,cval:x)

#Construct {stylename:value,...} to {stylename:Value(kind,value),...}
macro style(args: varargs[untyped]): Table[StyleName,Value] =
  #echo repr(args),args.treeRepr
  var s:seq[string]
  for arg in args:
    s.add arg[0].repr & ":" & "tovalue(" & arg[1].repr & ")"
  result = parseStmt("{" & s.join(",") & "}.toTable")

变体对象“Value”的宏访问器

macro getWithKind(style:Table[StyleName,Value],prop:StyleName,kind:Types):untyped=
  var accesor:string
  case kind.repr:
  of "Integer": accesor="ival"
  of "Float": accesor="fval"
  of "String": accesor="sval"
  of "Array": accesor="cval"
  result = parseStmt(style.repr & "[" & prop.repr & "]." & accesor)

#Transforms simple get(style,prop) call to getWithKind(style,prop,kind)
macro get(style:Table[StyleName,prop:StyleName):untyped=
  result = parseStmt(style.repr & ".getWithKind(" & prop.repr & ",kind=" & style.repr & "[" & prop.repr & "].kind)")

这是我得到的输出： 不能在另一个宏中调用宏吗？

let style1 = style(X=1,Y=2.0,Color=[0,0]) #build a table of (StyleName:Value)
echo style1  #output: {X: (kind: Integer,ival: 1),Y: (kind: Float,fval: 2.0),Color: (kind: Array,cval: [0,0])}
echo style1[X].ival  # output:1
echo style1[X].kind  # output:Integer
echo style1.getWithKind(X,kind=Integer)  # output:1
echo style1.get(X)  #(should get 1),output:

C:\Users\cravs\Desktop\test.nim(109,21) getWithKind
C:\nim-1.4.8\lib\core\macros.nim(558,17) parseStmt
C:\Users\cravs\Desktop\test.nim(119,12) template/generic instantiation of `get` from here
C:\nim-1.4.8\lib\core\macros.nim(557,7) template/generic instantiation of `getWithKind` from here
C:\nim-1.4.8\lib\core\macros.nim(558,17) Error: unhandled exception: C:\nim-1.4.8\lib\core\macros.nim(557,11) Error: invalid indentation [ValueError]

编辑： 这是另一个尝试

macro getWithKind(style:Table[StyleName,kind:Types):untyped=
  var accesor:string
  case kind.repr
  of "Integer": accesor="ival"
  of "Float": accesor="fval"
  of "String": accesor="sval"
  of "Array": accesor="cval"
  result = newDotExpr(newTree(nnkBracketExpr,style,prop),newIdentNode(accesor))
  #echo parseStmt(style.repr & "[" & prop.repr & "]." & accesor)

macro get(style:Table[StyleName,prop:StyleName):untyped=
  #result = parseStmt(style.repr & ".getWithKind(" & prop.repr & ",kind=" & style.repr & "[" & prop.repr & "].kind)")
  let kind = newDotExpr(newTree(nnkBracketExpr,newIdentNode("kind"))
  echo treeRepr kind
  quote do: 
    echo `kind` #prints Integer
    getWithKind(`style`,`prop`,kind=`kind`)


let style1 = style(X=1,output:

C:\Users\...\test.nim(127,3) Error: undeclared field: '' for type test.Value [declared in C:\Users\...\test.nim(80,6)]

解决方法

以下是您应该如何制作宏：

import macros,strutils,tables

type Types = enum Integer,Float,String,Array
type StyleName = enum X,Y,W,H,Left,Margin,Padding,Color,BorderColor

type Value = object
  case kind: Types
  of Integer: ival: int
  of Float: fval: float
  of String: sval: string
  of Array: cval: array[4,int]

proc toValue(x: float): Value = Value(kind: Float,fval: x)
proc toValue(x: int): Value = Value(kind: Integer,ival: x)
proc toValue(x: string): Value = Value(kind: String,sval: x)
proc toValue(x: array[4,int]): Value = Value(kind: Array,cval: x)

macro style(properties: untyped): Table[StyleName,Value] =
  var table = newNimNode(nnkTableConstr)
  
  properties.expectKind nnkStmtList
  
  for property in properties:
    property.expectKind nnkCall
    property.expectLen 2
    
    property[0].expectKind nnkIdent
    property[1].expectKind nnkStmtList
    property[1].expectLen 1

    let
      name = property[0]
      value = property[1][0]

    table.add(newTree(nnkExprColonExpr,name,quote do: `value`.toValue()))

  quote do:
    `table`.toTable()

let table = style:
  X: 10.0
  Y: 20.0
  Color: "ff00ff"
  Margin: [10,20,30,40]

echo table

我不知道您可以在宏中使用字符串，但它的匹配可以更好地操作 AST。通过这种方式，您还可以验证用户正在输入的内容。