Initial population.

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+% Copyright The Numerical Algorithms Group Limited 1992-94. All rights reserved.
+% !! DO NOT MODIFY THIS FILE BY HAND !! Created by ht.awk.
+\newcommand{\StreamXmpTitle}{Stream}
+\newcommand{\StreamXmpNumber}{9.76}
+%
+% =====================================================================
+\begin{page}{StreamXmpPage}{9.76 Stream}
+% =====================================================================
+\beginscroll
+
+A \spadtype{Stream} object is represented as a list whose last element contains the
+wherewithal to create the next element, should it ever be required.
+\xtc{
+Let \spad{ints} be the infinite stream of non-negative integers.
+}{
+\spadpaste{ints := [i for i in 0..] \bound{ints}}
+}
+By default, ten stream elements are calculated.
+This number may be changed to something else by the system command
+\spadcmd{)set streams calculate}.
+%-% \HDsyscmdindex{set streams calculate}{StreamXmpPage}{9.76}{Stream}
+For the display purposes of this book, we have chosen a smaller value.
+\xtc{
+More generally, you can construct a stream by specifying its initial
+value and a function which, when given an element, creates the next element.
+}{
+\spadpaste{f : List INT -> List INT \bound{fdec}}
+}
+\xtc{
+}{
+\spadpaste{f x == [x.1 + x.2, x.1] \bound{f}\free{fdec}}
+}
+\xtc{
+}{
+\spadpaste{fibs := [i.2 for i in [generate(f,[1,1])]] \bound{fibs}\free{f}}
+}
+\xtc{
+You can create the stream of odd non-negative integers by either filtering
+them from the integers, or by evaluating an expression for each integer.
+}{
+\spadpaste{[i for i in ints | odd? i] \free{ints}}
+}
+\xtc{
+}{
+\spadpaste{odds := [2*i+1 for i in ints]\bound{odds}\free{ints}}
+}
+\xtc{
+You can accumulate the initial segments of a stream using the
+\spadfunFrom{scan}{StreamFunctions2} operation.
+}{
+\spadpaste{scan(0,+,odds) \free{odds}}
+}
+\xtc{
+The corresponding elements of
+two or more streams can be combined in this way.
+}{
+\spadpaste{[i*j for i in ints for j in odds]\free{ints} \free{odds}}
+}
+\xtc{
+}{
+\spadpaste{map(*,ints,odds)\free{ints odds}}
+}
+\xtc{
+Many operations similar to those applicable to lists are available for
+streams.
+}{
+\spadpaste{first ints \free{ints}}
+}
+\xtc{
+}{
+\spadpaste{rest ints \free{ints}}
+}
+\xtc{
+}{
+\spadpaste{fibs 20 \free{fibs}}
+}
+The packages \spadtype{StreamFunctions1},
+%-% \HDexptypeindex{StreamFunctions1}{StreamXmpPage}{9.76}{Stream}
+\spadtype{StreamFunctions2} and
+%-% \HDexptypeindex{StreamFunctions2}{StreamXmpPage}{9.76}{Stream}
+\spadtype{StreamFunctions3} export some useful stream manipulation
+operations.
+%-% \HDexptypeindex{StreamFunctions3}{StreamXmpPage}{9.76}{Stream}
+For more information, see
+\downlink{``\ugLangItsTitle''}{ugLangItsPage} in Section \ugLangItsNumber\ignore{ugLangIts},
+\downlink{``\ugProblemSeriesTitle''}{ugProblemSeriesPage} in Section \ugProblemSeriesNumber\ignore{ugProblemSeries},
+\downlink{`ContinuedFraction'}{ContinuedFractionXmpPage}\ignore{ContinuedFraction}, and
+\downlink{`List'}{ListXmpPage}\ignore{List}.
+%
+\showBlurb{Stream}
+\endscroll
+\autobuttons
+\end{page}
+%