dsl.nim

# module a

import std/[macros, typetraits]

type
  ModelName = distinct string

  Spec*[T] = object
    model: ModelName

  Machine*[T] = object
    data*: T

  Void* = object

func `$`*(x: ModelName): string =
  x.string

func init*(T: typedesc[Void]): T =
  T()

macro spec*(): auto =
  result = quote do:
    Spec[Void](model: ModelName(Void.name))

macro spec*(T: typedesc): auto =
  result = quote do:
    Spec[`T`](model: ModelName(`T`.name))

func compile*[T](spec: Spec[T]): Machine[T] =
  mixin init
  Machine[T](data: T.init)

# module b
# import ./a

type MyData* = object
  x: string

func init*(T: typedesc[MyData], x: string): T =
  T(x: x)

func init*(T: typedesc[MyData]): T =
  T(x: "default")

const spec1a = spec()
let   spec1b = spec()

const machine1a = spec1a.compile
let   machine1b = spec1b.compile

echo ""
echo spec1a
echo ""
echo spec1b
echo ""
echo machine1a
echo ""
echo machine1b
echo ""

const spec2a = MyData.spec
let   spec2b = MyData.spec

const machine2a = spec2a.compile
let   machine2b = spec2b.compile

echo spec2a
echo ""
echo spec2b
echo ""
echo machine2a
echo ""
echo machine2b
echo ""

# output
# ----------------------
# (model: Void)
#
# (model: Void)
#
# (data: ())
#
# (data: ())
#
# (model: MyData)
#
# (model: MyData)
#
# (data: (x: "default"))
#
# (data: (x: "default"))