bar.nim

import os, stew/faux_closures, threadpool

type
  MyString* = distinct cstring

proc mine*(input: string): MyString =
  input.cstring.MyString

proc `$`*(input: MyString): string =
  $(input.cstring)

proc sendSignal(data: string, name: string) =
  echo name & ": " & data

template spawnAndSend(name: string, exprToSend: untyped) =
  let nameCstr = name.mine
  proc payload {.fauxClosure.} =
    let data: string = exprToSend
    sendSignal(data, $nameCstr)
  spawn payload()

# L20 triggers a compiler error:
# bar.nim(20, 16) Error: type mismatch: got <MyString>
# but expected one of:
# proc payload_16600094(nameCstr`gensym16591097_16600096: distinct[cstring])
# first type mismatch at position: 1
#   required type for nameCstr`gensym16591097: distinct cstring
#   but expression 'nameCstr`gensym16591097' is of type: MyString
#
# expression: payload_16600094(nameCstr`gensym16591097)

proc foo(bar: string) =
  spawnAndSend(bar) do:
    "foo"

foo("bar")

sleep(2)

# Run with `./env.sh nim c -r --threads:on --tlsEmulation:off bar.nim`