functor Emit(I: IL) = struct
  structure I = I

  structure P = I.P
  structure D = P.D
  structure PP = P.P

  val file = ref NONE

  local
    fun output s =
    let
      val outstream = valOf $ !file
    in
      TextIO.output (outstream, s)
    end

    val ctx = ((false, makePrintfBase output),
      fn (_: bool * ((string -> unit) * (unit -> unit))) => ())
  in
    fun fprint g = Fold.fold ctx g
  end

  fun fprintt g = fprint `"\t" g

  fun fprinttn g =
    fprintt (fn (a, _) => g (a, fn (_, out) => (Printf out `"\n" %)))

  fun handleBSS objsZI =
  let
    val () = fprint `"section .bss\n" %

    fun handleObj (id, _, t, _, _) =
    let
      val align = P.alignOfType t
      val size = P.sizeOfType t
    in
      fprinttn `"align\t" W align %;
      fprint PP.? id `":\tresb " W size `"\n" %
    end
  in
    List.app handleObj objsZI
  end

  fun dd size w =
  let
    val cmd =
      case size of
        0w1 => "db"
      | 0w2 => "dw"
      | 0w4 => "dd"
      | 0w8 => "dq"
      | _ => raise Unreachable
  in
    fprint `cmd `" " W w %
  end

  fun emitAggrLayout id =
  let
    val (_, size, layout) = D.get P.iniLayouts id

    val () = fprint `"\n" %

    fun getPadding offset t [] = size - (offset + P.sizeOfType t)
      | getPadding offset t ({ offset = offset', ... } :: _) =
        offset' - (offset + P.sizeOfType t)

    fun emitScalars ({ offset, t, value } :: tail) =
    let
      val () = fprint `"\t" %
      val () = dd (P.sizeOfType t) value
      val padding = getPadding offset t tail
    in
      if padding > 0w0 then
        fprint `"\n\tresb " W padding `"\n" %
      else
        fprint `"\n" %;
      emitScalars tail
    end
      | emitScalars [] = ()
  in
    emitScalars layout
  end

  fun handleData objs =
  let
    val () = fprint `"section .data\n" %

    fun emitLayout (id, _, t, ini, _) =
    let
      val align = P.alignOfType t
      val () = fprinttn `"align\t" W align %
      val () = fprint PP.? id `":" %
    in
      case ini of
        P.CiniLayout id => emitAggrLayout id
      | P.CiniExpr _ => raise Unreachable
    end
  in
    List.app emitLayout objs
  end

  fun handleStrlits strlits =
  let
    fun f id = fprint `".S" I id `":\tdb " `(PP.?? id) `", 0\n" %
  in
    fprint `"\n" %;
    List.app f strlits
  end

  fun handleLocalIniLayouts () =
  let
    fun f (_, (true, _, _)) = ()
      | f (n, (false, _, _)) = (
        fprint `"\talign 16\n" %;
        fprint `".I" I n `":" %;
        emitAggrLayout n
      )
  in
    D.appi f P.iniLayouts
  end

  fun openFile fname = file := SOME (TextIO.openOut fname)

  fun emit fname
    (I.Ctx { globSyms, extSyms, objsZI, objs, strlits, ... }) =
  let
    val () = openFile fname

    val () = List.app (fn gs => fprint `"global " PP.? gs `"\n" %) globSyms
    val () = List.app (fn es => fprint `"extern " PP.? es `"\n" %) extSyms

    val () = handleBSS objsZI
    val () = handleData objs
    val () = handleStrlits strlits
    val () = handleLocalIniLayouts ()
  in
    ()
  end
end