gistfile1.nim

proc apply[OpSymbol, T: tuple](t: T) : auto = 
  macro:
    var retType = newNimrodType(ntkTuple)
    for fields in T:
       retType.add(inferType(newCall(OpSymbol, T[1])) #skiping some detail

    var transformedExp = .. build and expression of the type (OpSymbol(T[0]), OpSymbol(T[1]), )

    template:
      var x : retType = transformedExp

  return x

macro getTransformedTupleType(t: symbol) {.late.} =
  # the same code

proc apply ... = type(getTransformedTupleType(t))