ImplementSuffix
===============

<:ImplementSuffix:> is a pass for the <:SXML:>
<:IntermediateLanguage:>, invoked from <:SXMLSimplify:>.

== Description ==

This pass implements the `TopLevel_setSuffix` primitive, which
installs a function to exit the program.

== Implementation ==

* <!ViewGitFile(mlton,master,mlton/xml/implement-suffix.fun)>

== Details and Notes ==

<:ImplementSuffix:> works by introducing a new `ref` cell to contain
the function of type `unit -> unit` that should be called on program
exit.

* The following code (appropriately alpha-converted) is appended to the beginning of the <:SXML:> program:
+
[source,sml]
----
val z_0 =
  fn a_0 =>
  let
    val x_0 =
      "toplevel suffix not installed"
    val x_1 =
      MLton_bug (x_0)
  in
    x_1
  end
val topLevelSuffixCell =
  Ref_ref (z_0)
----

* Any occurrence of
+
[source,sml]
----
val x_0 =
  TopLevel_setSuffix (f_0)
----
+
is rewritten to
+
[source,sml]
----
val x_0 =
  Ref_assign (topLevelSuffixCell, f_0)
----

* The following code (appropriately alpha-converted) is appended to the end of the <:SXML:> program:
+
[source,sml]
----
val f_0 =
  Ref_deref (topLevelSuffixCell)
val z_0 =
  ()
val x_0 =
  f_0 z_0
----