doc/guide/src/ImplementSuffix.adoc

   1 ImplementSuffix
   2 ===============
   3
   4 <:ImplementSuffix:> is a pass for the <:SXML:>
   5 <:IntermediateLanguage:>, invoked from <:SXMLSimplify:>.
   6
   7 == Description ==
   8
   9 This pass implements the `TopLevel_setSuffix` primitive, which
  10 installs a function to exit the program.
  11
  12 == Implementation ==
  13
  14 * <!ViewGitFile(mlton,master,mlton/xml/implement-suffix.fun)>
  15
  16 == Details and Notes ==
  17
  18 <:ImplementSuffix:> works by introducing a new `ref` cell to contain
  19 the function of type `unit -> unit` that should be called on program
  20 exit.
  21
  22 * The following code (appropriately alpha-converted) is appended to the beginning of the <:SXML:> program:
  23 +
  24 [source,sml]
  25 ----
  26 val z_0 =
  27   fn a_0 =>
  28   let
  29     val x_0 =
  30       "toplevel suffix not installed"
  31     val x_1 =
  32       MLton_bug (x_0)
  33   in
  34     x_1
  35   end
  36 val topLevelSuffixCell =
  37   Ref_ref (z_0)
  38 ----
  39
  40 * Any occurrence of
  41 +
  42 [source,sml]
  43 ----
  44 val x_0 =
  45   TopLevel_setSuffix (f_0)
  46 ----
  47 +
  48 is rewritten to
  49 +
  50 [source,sml]
  51 ----
  52 val x_0 =
  53   Ref_assign (topLevelSuffixCell, f_0)
  54 ----
  55
  56 * The following code (appropriately alpha-converted) is appended to the end of the <:SXML:> program:
  57 +
  58 [source,sml]
  59 ----
  60 val f_0 =
  61   Ref_deref (topLevelSuffixCell)
  62 val z_0 =
  63   ()
  64 val x_0 =
  65   f_0 z_0
  66 ----