app.nim

# compile with
# nim c --app:dll -o:app.dll app.nim
# nim c --app:exe -o:app.exe app.nim
# then run app.exe

when compileOption("app", "exe"):
  type App = ptr object
  {.pragma: appImport, importc, nimcall, dynlib: "app".}
  proc newApp() :App {.appImport.}
  proc run(app :App) {.appImport.}

  var app = newApp()
  app.run
elif compileOption("app", "dll"):
  type App = ptr object
  {.pragma: appExport, exportc, nimcall, dynlib.}
  proc newApp() :App {.appExport.} = nil
  proc run(app :App) {.appExport.} = echo("run() from DLL")