Add FOREACH IN ARRAY looping to plpgsql.

(I'm not entirely sure that we've finished bikeshedding the syntax details,
but the functionality seems OK.)

Pavel Stehule, reviewed by Stephen Frost and Tom Lane

doc/src/sgml/plpgsql.sgml

@@ -1263,7 +1263,7 @@ EXECUTE 'UPDATE tbl SET '
 <programlisting>
 EXECUTE format('UPDATE tbl SET %I = %L WHERE key = %L', colname, newvalue, keyvalue);
 </programlisting>
-     The <function>format</function> function can be used in conjunction with 
+     The <function>format</function> function can be used in conjunction with
      the <literal>USING</literal> clause:
 <programlisting>
 EXECUTE format('UPDATE tbl SET %I = $1 WHERE key = $2', colname)
@@ -1356,19 +1356,15 @@ GET DIAGNOSTICS integer_var = ROW_COUNT;
             true if it successfully repositions the cursor, false otherwise.
            </para>
           </listitem>
-
           <listitem>
            <para>
-            A <command>FOR</> statement sets <literal>FOUND</literal> true
-            if it iterates one or more times, else false.  This applies to
-            all four variants of the <command>FOR</> statement (integer
-            <command>FOR</> loops, record-set <command>FOR</> loops,
-            dynamic record-set <command>FOR</> loops, and cursor
-            <command>FOR</> loops).
+            A <command>FOR</> or <command>FOREACH</> statement sets
+            <literal>FOUND</literal> true
+            if it iterates one or more times, else false.
             <literal>FOUND</literal> is set this way when the
-            <command>FOR</> loop exits; inside the execution of the loop,
+            loop exits; inside the execution of the loop,
             <literal>FOUND</literal> is not modified by the
-            <command>FOR</> statement, although it might be changed by the
+            loop statement, although it might be changed by the
             execution of other statements within the loop body.
            </para>
           </listitem>
@@ -1910,9 +1906,9 @@ END CASE;
 
     <para>
      With the <literal>LOOP</>, <literal>EXIT</>,
-     <literal>CONTINUE</>, <literal>WHILE</>, and <literal>FOR</>
-     statements, you can arrange for your <application>PL/pgSQL</>
-     function to repeat a series of commands.
+     <literal>CONTINUE</>, <literal>WHILE</>, <literal>FOR</>,
+     and <literal>FOREACH</> statements, you can arrange for your
+     <application>PL/pgSQL</> function to repeat a series of commands.
     </para>
 
     <sect3>
@@ -2238,6 +2234,90 @@ END LOOP <optional> <replaceable>label</replaceable> </optional>;
     </para>
    </sect2>
 
+   <sect2 id="plpgsql-foreach-array">
+    <title>Looping Through Arrays</title>
+
+    <para>
+     The <literal>FOREACH</> loop is much like a <literal>FOR</> loop,
+     but instead of iterating through the rows returned by a SQL query,
+     it iterates through the elements of an array value.
+     (In general, <literal>FOREACH</> is meant for looping through
+     components of a composite-valued expression; variants for looping
+     through composites besides arrays may be added in future.)
+     The <literal>FOREACH</> statement to loop over an array is:
+
+<synopsis>
+<optional> &lt;&lt;<replaceable>label</replaceable>&gt;&gt; </optional>
+FOREACH <replaceable>target</replaceable> <optional> SLICE <replaceable>number</replaceable> </optional> IN ARRAY <replaceable>expression</replaceable> LOOP
+    <replaceable>statements</replaceable>
+END LOOP <optional> <replaceable>label</replaceable> </optional>;
+</synopsis>
+    </para>
+
+    <para>
+     Without <literal>SLICE</>, or if <literal>SLICE 0</> is specified,
+     the loop iterates through individual elements of the array produced
+     by evaluating the <replaceable>expression</replaceable>.
+     The <replaceable>target</replaceable> variable is assigned each
+     element value in sequence, and the loop body is executed for each element.
+     Here is an example of looping through the elements of an integer
+     array:
+
+<programlisting>
+CREATE FUNCTION sum(int[]) RETURNS int8 AS $$
+DECLARE
+  s int8 := 0;
+  x int;
+BEGIN
+  FOREACH x IN ARRAY $1
+  LOOP
+    s := s + x;
+  END LOOP;
+  RETURN s;
+END;
+$$ LANGUAGE plpgsql;
+</programlisting>
+
+     The elements are visited in storage order, regardless of the number of
+     array dimensions.  Although the <replaceable>target</replaceable> is
+     usually just a single variable, it can be a list of variables when
+     looping through an array of composite values (records).  In that case,
+     for each array element, the variables are assigned from successive
+     columns of the composite value.
+    </para>
+
+    <para>
+     With a positive <literal>SLICE</> value, <literal>FOREACH</>
+     iterates through slices of the array rather than single elements.
+     The <literal>SLICE</> value must be an integer constant not larger
+     than the number of dimensions of the array.  The
+     <replaceable>target</replaceable> variable must be an array,
+     and it receives successive slices of the array value, where each slice
+     is of the number of dimensions specified by <literal>SLICE</>.
+     Here is an example of iterating through one-dimensional slices:
+
+<programlisting>
+CREATE FUNCTION scan_rows(int[]) RETURNS void AS $$
+DECLARE
+  x int[];
+BEGIN
+  FOREACH x SLICE 1 IN ARRAY $1
+  LOOP
+    RAISE NOTICE 'row = %', x;
+  END LOOP;
+END;
+$$ LANGUAGE plpgsql;
+
+SELECT scan_rows(ARRAY[[1,2,3],[4,5,6],[7,8,9],[10,11,12]]);
+
+NOTICE:  row = {1,2,3}
+NOTICE:  row = {4,5,6}
+NOTICE:  row = {7,8,9}
+NOTICE:  row = {10,11,12}
+</programlisting>
+    </para>
+   </sect2>
+
    <sect2 id="plpgsql-error-trapping">
     <title>Trapping Errors</title>