import std/macros

macro returnType(P: typedesc): untyped =
  let bracketExpr = P.getTypeImpl
  assert bracketExpr.kind == nnkBracketExpr
  let typeDef = bracketExpr[1].getImpl
  assert typeDef.kind == nnkTypeDef
  let procDef = typeDef[2]
  assert procDef.typeKind == ntyProc
  let params = procDef[0]
  params[0]
# (@pmunch)