added docs for const_pre/postorder_iterator

[ginac.git] / doc / tutorial / ginac.texi

diff --git a/doc/tutorial/ginac.texi b/doc/tutorial/ginac.texi
index c02ffc95331338be519c0d3ed321cd9a86ce579c..0d668ad265ed285ec8e169b668280f7d31dfbf6f 100644 (file)
--- a/doc/tutorial/ginac.texi
+++ b/doc/tutorial/ginac.texi
@@ -3149,28 +3149,117 @@ for an explanation of these.
 
 
 @subsection Accessing subexpressions
-@cindex @code{nops()}
-@cindex @code{op()}
 @cindex container
-@cindex @code{relational} (class)
 
-GiNaC provides the two methods
+Many GiNaC classes, like @code{add}, @code{mul}, @code{lst}, and
+@code{function}, act as containers for subexpressions. For example, the
+subexpressions of a sum (an @code{add} object) are the individual terms,
+and the subexpressions of a @code{function} are the function's arguments.
+
+@cindex @code{nops()}
+@cindex @code{op()}
+GiNaC provides several ways of accessing subexpressions. The first way is to
+use the two methods
 
 @example
 size_t ex::nops();
 ex ex::op(size_t i);
 @end example
 
-for accessing the subexpressions in the container-like GiNaC classes like
-@code{add}, @code{mul}, @code{lst}, and @code{function}. @code{nops()}
-determines the number of subexpressions (@samp{operands}) contained, while
-@code{op()} returns the @code{i}-th (0..@code{nops()-1}) subexpression.
-In the case of a @code{power} object, @code{op(0)} will return the basis
-and @code{op(1)} the exponent. For @code{indexed} objects, @code{op(0)}
-is the base expression and @code{op(i)}, @math{i>0} are the indices.
+@code{nops()} determines the number of subexpressions (operands) contained
+in the expression, while @code{op(i)} returns the @code{i}-th
+(0..@code{nops()-1}) subexpression. In the case of a @code{power} object,
+@code{op(0)} will return the basis and @code{op(1)} the exponent. For
+@code{indexed} objects, @code{op(0)} is the base expression and @code{op(i)},
+@math{i>0} are the indices.
 
-The left-hand and right-hand side expressions of objects of class
-@code{relational} (and only of these) can also be accessed with the methods
+@cindex iterators
+@cindex @code{const_iterator}
+The second way to access subexpressions is via the STL-style random-access
+iterator class @code{const_iterator} and the methods
+
+@example
+const_iterator ex::begin();
+const_iterator ex::end();
+@end example
+
+@code{begin()} returns an iterator referring to the first subexpression;
+@code{end()} returns an iterator which is one-past the last subexpression.
+If the expression has no subexpressions, then @code{begin() == end()}. These
+iterators can also be used in conjunction with non-modifying STL algorithms.
+
+Here is an example that (non-recursively) prints the subexpressions of a
+given expression in three different ways:
+
+@example
+@{
+    ex e = ...
+
+    // with nops()/op()
+    for (size_t i = 0; i != e.nops(); ++i)
+        cout << e.op(i) << endl;
+
+    // with iterators
+    for (const_iterator i = e.begin(); i != e.end(); ++i)
+        cout << *i << endl;
+
+    // with iterators and STL copy()
+    std::copy(e.begin(), e.end(), std::ostream_iterator<ex>(cout, "\n"));
+@}
+@end example
+
+@cindex @code{const_preorder_iterator}
+@cindex @code{const_postorder_iterator}
+@code{op()}/@code{nops()} and @code{const_iterator} only access an
+expression's immediate children. GiNaC provides two additional iterator
+classes, @code{const_preorder_iterator} and @code{const_postorder_iterator},
+that iterate over all objects in an expression tree, in preorder or postorder,
+respectively. They are STL-style forward iterators, and are created with the
+methods
+
+@example
+const_preorder_iterator ex::preorder_begin();
+const_preorder_iterator ex::preorder_end();
+const_postorder_iterator ex::postorder_begin();
+const_postorder_iterator ex::postorder_end();
+@end example
+
+The following example illustrates the differences between
+@code{const_iterator}, @code{const_preorder_iterator}, and
+@code{const_postorder_iterator}:
+
+@example
+@{
+    symbol A("A"), B("B"), C("C");
+    ex e = lst(lst(A, B), C);
+
+    std::copy(e.begin(), e.end(),
+              std::ostream_iterator<ex>(cout, "\n"));
+    // @{A,B@}
+    // C
+
+    std::copy(e.preorder_begin(), e.preorder_end(),
+              std::ostream_iterator<ex>(cout, "\n"));
+    // @{@{A,B@},C@}
+    // @{A,B@}
+    // A
+    // B
+    // C
+
+    std::copy(e.postorder_begin(), e.postorder_end(),
+              std::ostream_iterator<ex>(cout, "\n"));
+    // A
+    // B
+    // @{A,B@}
+    // C
+    // @{@{A,B@},C@}
+@}
+@end example
+
+@cindex @code{relational} (class)
+Finally, the left-hand side and right-hand side expressions of objects of
+class @code{relational} (and only of these) can also be accessed with the
+methods
 
 @example
 ex ex::lhs();
@@ -4096,6 +4185,21 @@ lst gather_indices(const ex & e)
 @}
 @end example
 
+Alternatively, you could use pre- or postorder iterators for the tree
+traversal:
+
+@example
+lst gather_indices(const ex & e)
+@{
+    gather_indices_visitor v;
+    for (const_preorder_iterator i = e.preorder_begin();
+         i != e.preorder_end(); ++i) @{
+        i->accept(v);
+    @}
+    return v.get_result();
+@}
+@end example
+
 
 @node Polynomial Arithmetic, Rational Expressions, Visitors and Tree Traversal, Methods and Functions
 @c    node-name, next, previous, up