Initial population.

1 files changed, 57 insertions, 0 deletions

diff --git a/src/hyper/pages/VOID.ht b/src/hyper/pages/VOID.ht
new file mode 100644
index 00000000..4dc87ca3
--- /dev/null
+++ b/src/hyper/pages/VOID.ht
@@ -0,0 +1,57 @@
+% Copyright The Numerical Algorithms Group Limited 1992-94. All rights reserved.
+% !! DO NOT MODIFY THIS FILE BY HAND !! Created by ht.awk.
+\newcommand{\VoidXmpTitle}{Void}
+\newcommand{\VoidXmpNumber}{9.86}
+%
+% =====================================================================
+\begin{page}{VoidXmpPage}{9.86 Void}
+% =====================================================================
+\beginscroll
+
+When an expression is not in a value context, it is given type \spadtype{Void}.
+For example, in the expression
+\begin{verbatim}
+r := (a; b; if c then d else e; f)
+\end{verbatim}
+values are used only from the subexpressions \spad{c} and \spad{f}: all
+others are thrown away.
+The subexpressions \spad{a}, \spad{b}, \spad{d} and \spad{e}
+are evaluated for side-effects only and have type \spadtype{Void}.
+There is a unique value of type \spadtype{Void}.
+
+\xtc{
+You will most often see results of type \spadtype{Void} when you
+declare a variable.
+}{
+\spadpaste{a : Integer}
+}
+\noOutputXtc{
+Usually no output is displayed for \spadtype{Void} results.
+You can force the display of a rather ugly object by issuing
+\spadcmd{)set message void on}.
+%-% \HDsyscmdindex{set message void}{VoidXmpPage}{9.86}{Void}
+}{
+\spadpaste{)set message void on}
+}
+\xtc{
+}{
+\spadpaste{b : Fraction Integer}
+}
+\noOutputXtc{
+}{
+\spadpaste{)set message void off}
+}
+\xtc{
+All values can be converted to type \spadtype{Void}.
+}{
+\spadpaste{3::Void \bound{prev}}
+}
+\xtc{
+Once a value has been converted to \spadtype{Void}, it cannot be recovered.
+}{
+\spadpaste{\% :: PositiveInteger \free{prev}}
+}
+\endscroll
+\autobuttons
+\end{page}
+%