Empty sequences: changes by Tobias compacted (#675)

* Empty sequence changes by Tobias * that empty line... * just handy. * Made p. 505 long by 1 Co-authored-by: Tobias Wrigstad <tobias.wrigstad@it.uu.se>

Author: martin-henz

xml/chapter4/section1/subsection2.xml

@@ -567,8 +567,7 @@ null
 and omit their declarations if they just access the obvious list elements.
  </TEXT>
  <TEXT>
-We provide a constructor for literals, which will come in handy in
-section<SPACE/><REF NAME="sec:query-syntax"/>.
+We provide a constructor for literals, which will come in handy.
 <SNIPPET PAGE="369" POSTPADDING="no">
  <INDEX><DECLARATION>make_literal</DECLARATION></INDEX>
  <NAME>make_literal</NAME>

xml/chapter5/section4/subsection1.xml

@@ -738,7 +738,7 @@ compound-apply
  statements is kept in <JAVASCRIPTINLINE>unev</JAVASCRIPTINLINE>.
  At <JAVASCRIPTINLINE>ev_sequence</JAVASCRIPTINLINE> we place the sequence of
  statements to be evaluated in <JAVASCRIPTINLINE>unev</JAVASCRIPTINLINE>. If the
- sequence is empty, we jump straight to
+ sequence is empty, we set <JAVASCRIPTINLINE>val</JAVASCRIPTINLINE> to <JAVASCRIPTINLINE>undefined</JAVASCRIPTINLINE> and jump to
  <JAVASCRIPTINLINE>continue</JAVASCRIPTINLINE> via
  <JAVASCRIPTINLINE>ev_sequence_empty</JAVASCRIPTINLINE>. Otherwise we start the
  sequence-evaluation loop, first saving the value of <JAVASCRIPTINLINE>continue</JAVASCRIPTINLINE> on the stack, because
@@ -801,10 +801,12 @@ compound-apply
  go_to(label("eval_dispatch")),
 
 "ev_sequence_empty",
+ assign("val", constant(undefined)),
  go_to(reg("continue")), 
  </JAVASCRIPT>
  </SNIPPET>
 
+ <LONG_PAGE lines="1"/>
  <TEXT>
  Unlike <JAVASCRIPTINLINE>eval_sequence</JAVASCRIPTINLINE> in the metacircular
  evaluator, <JAVASCRIPTINLINE>ev_sequence</JAVASCRIPTINLINE> does not need to check whether a return statement was

xml/chapter5/section5/subsection2.xml

@@ -756,11 +756,11 @@ function compile_conditional(component, target, linkage) {
  <JAVASCRIPT>
 function compile_sequence(seq, target, linkage) {
  return is_empty_sequence(seq)
- ? empty_instruction_sequence()
+ ? compile_literal(make_literal(undefined), target, linkage)
  : is_last_statement(seq) ||
  is_return_statement(first_statement(seq))
  ? compile(first_statement(seq), target, linkage)
- : preserving(list("env"),
+ : preserving(list("env", "continue"),
  compile(first_statement(seq), target, "next"),
  compile_sequence(rest_statements(seq), 
  target, linkage));