How to write accesors for kind Variants in Nim - variant

Question

Trying to write accesors to get a value of an object with a kind member, I get invalid indentation error in a macro I am not sure why
I imagine I might be building macros wrong but if there is a better way to abstract type kinds in objects it would be great to know.
Here is the implementation I am working:
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")
Macro accesors for the variant object "Value"
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,Value], prop:StyleName):untyped=
result = parseStmt(style.repr & ".getWithKind(" & prop.repr & ", kind=" & style.repr & "[" & prop.repr & "].kind)")
This is the output I get:
Is it not possible to call a macro inside another macro?
let style1 = style(X=1,Y=2.0,Color=[0,0,0,0]) #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, 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]
Edit:
Here is another attempt
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 = newDotExpr(newTree(nnkBracketExpr,style,prop), newIdentNode(accesor))
#echo parseStmt(style.repr & "[" & prop.repr & "]." & accesor)
macro get(style:Table[StyleName,Value], prop:StyleName):untyped=
#result = parseStmt(style.repr & ".getWithKind(" & prop.repr & ", kind=" & style.repr & "[" & prop.repr & "].kind)")
let kind = newDotExpr(newTree(nnkBracketExpr,style,prop), newIdentNode("kind"))
echo treeRepr kind
quote do:
echo `kind` #prints Integer
getWithKind(`style`,`prop`,kind=`kind`)
let style1 = style(X=1,Y=2.0,Color=[0,0,0,0]) #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, 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\...\test.nim(127, 3) Error: undeclared field: '' for type test.Value [declared in C:\Users\...\test.nim(80, 6)]

Answer 1

Here is how you should make macros:
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
I had no idea you can use strings in macro but its match better to manipulate AST instead. This way you can also verify what user is inputting.