refs https://github.com/nim-lang/RFCs/issues/332#issuecomment-778106052

caseStmtMacros.nim

when true:
  import macros
  from typetraits import distinctBase
  {.experimental: "caseStmtMacros".}

  type CustomCase1[T]= distinct T
  template customCase1[T](a: T): CustomCase1[T] = CustomCase1[T](a)
  proc `==`[T](a: CustomCase1[T], b: T): bool = a.distinctBase == b

  type CustomCase2[T]= distinct T
  template customCase2[T](a: T): CustomCase2[T] = CustomCase2[T](a)
  proc `==`[T](a: CustomCase2[T], b: T): bool = a.distinctBase == b

  macro `case`(n: CustomCase1): untyped =
    result = newTree(nnkIfStmt)
    let selector = n[0]
    for i in 1 ..< n.len:
      let it = n[i]
      case it.kind
      of nnkElse, nnkElifBranch, nnkElifExpr, nnkElseExpr:
        result.add it
      of nnkOfBranch:
        for j in 0..it.len-2:
          let cond = newCall("==", selector, it[j])
          result.add newTree(nnkElifBranch, cond, it[^1])
      else:
        error "custom 'case' for tuple cannot handle this node", it
    result = quote do:
      echo "v1"
      `result`

  macro `case`(n: CustomCase2): untyped =
    result = newTree(nnkIfStmt)
    let selector = n[0]
    for i in 1 ..< n.len:
      let it = n[i]
      case it.kind
      of nnkElse, nnkElifBranch, nnkElifExpr, nnkElseExpr:
        result.add it
      of nnkOfBranch:
        for j in 0..it.len-2:
          let cond = newCall("==", selector, it[j])
          result.add newTree(nnkElifBranch, cond, it[^1])
      else:
        error "custom 'case' for tuple cannot handle this node", it
    result = quote do:
      echo "v2"
      `result`

  case (("foo", 78)).customCase1
  of ("foo", 78): echo "yes"
  of ("bar", 88): echo "no"
  else: discard

  case (("foo", 78)).customCase2
  of ("foo", 78): echo "yes"
  of ("bar", 88): echo "no"
  else: discard