gistfile1.nim

type TFoo* = object
  yatamo*: string

proc yo*(a: TFoo, wa: int): string
proc ha*(a: TFoo, woo: string): int

when defined(macosx):
  TFoo.bar = TMacBar # Works iff the code is ran statically
  TFoo.baz = TMacBaz
  
  proc yo(a: TFoo, wa: int): string =
    a.bar.str
  proc ha(a: TFoo, woo: string): int=
    a.baz.int
elif defined(windows):
  TFoo.bar = TWindowsBar
  TFoo.bar = TWindowsBaz
  # and so on
else:
  TFoo.bar = TUnixBar
  # Unix has no UnixBaz