Adds index, and also add examples. Closes #2835

Author: JJ

doc/Language/functions.pod6

@@ -99,12 +99,13 @@ Or even
 
     say { $^a ** 2 + $^b ** 2 }(3, 4)            # OUTPUT: «25␤»
 
-
+X<|pointy blocks>
 =head2 X«Blocks and lambdas|syntax,->»
 
-Whenever you see something like C«{ $_ + 42 }»,
-C«-> $a, $b { $a ** $b }», or C«{ $^text.indent($:spaces) }», that's
-L<Block|/type/Block> syntax. It's used after every C<if>, C<for>, C<while>, etc.
+Whenever you see something like C«{ $_ + 42 }», C«-> $a, $b { $a ** $b }», or
+C«{ $^text.indent($:spaces) }», that's L<Block|/type/Block> syntax; the C<->> is
+considered also part of the block. Statements such as C<if>, C<for>, C<while>
+are followed by these kind of blocks.
 
     for 1, 2, 3, 4 -> $a, $b {
         say $a ~ $b;
@@ -115,7 +116,17 @@ They can also be used on their own as anonymous blocks of code.
 
     say { $^a ** 2 + $^b ** 2}(3, 4) # OUTPUT: «25␤»
 
-For block syntax details, see the documentation for the L<Block|/type/Block> type.
+Please note that this implies that, despite the fact that statements such as
+C<if> do not define a topic variable, they actually can:
+
+=for code
+my $foo = 33;
+if $foo ** 33 -> $a {
+    say "$a is not null"; #
+} # OUTPUT: «129110040087761027839616029934664535539337183380513 is not null␤»
+
+For block syntax details, see the documentation for the L<Block|/type/Block>
+type.
 
 =head2 Signatures