Address #1390

@Zoffixnet, awaiting your review

perl6.html.markdown

@@ -1,10 +1,9 @@
 ---
-name: perl6
 category: language
 language: perl6
 filename: learnperl6.pl
 contributors:
-    - ["Nami-Doc", "http://github.com/Nami-Doc"]
+    - ["vendethiel", "http://github.com/vendethiel"]
 ---
 
 Perl 6 is a highly capable, feature-rich programming language made for at
@@ -374,6 +373,8 @@ say @array[^10]; # you can pass arrays as subscripts and it'll return
 say join(' ', @array[15..*]); #=> 15 16 17 18 19
 # which is equivalent to:
 say join(' ', @array[-> $n { 15..$n }]);
+# Note: if you try to do either of those with an infinite loop,
+#       you'll trigger an infinite loop (your program won't finish)
 
 # You can use that in most places you'd expect, even assigning to an array
 my @numbers = ^20;
@@ -763,8 +764,9 @@ try {
 #  and `enum`) are actually packages. (Packages are the lowest common denominator)
 # Packages are important - especially as Perl is well-known for CPAN,
 #  the Comprehensive Perl Archive Network.
-# You usually don't use packages directly: you use `class Package::Name::Here;`,
-# or if you only want to export variables/subs, you can use `module`:
+# You're not supposed to use the package keyword, usually:
+#  you use `class Package::Name::Here;` to declare a class,
+#  or if you only want to export variables/subs, you can use `module`:
 module Hello::World { # Bracketed form
                       # If `Hello` doesn't exist yet, it'll just be a "stub",
                       #  that can be redeclared as something else later.
@@ -774,11 +776,6 @@ unit module Parse::Text; # file-scoped form
 grammar Parse::Text::Grammar { # A grammar is a package, which you could `use`
 }
 
-# NOTE for Perl 5 users: even though the `package` keyword exists,
-#  the braceless form is invalid (to catch a "perl5ism"). This will error out:
-# package Foo; # because Perl 6 will think the entire file is Perl 5
-# Just use `module` or the brace version of `package`.
-
 # You can use a module (bring its declarations into scope) with `use`
 use JSON::Tiny; # if you installed Rakudo* or Panda, you'll have this module
 say from-json('[1]').perl; #=> [1]
@@ -870,8 +867,16 @@ LEAVE { say "Runs everytime you leave a block, even when an exception
 
 PRE { say "Asserts a precondition at every block entry,
     before ENTER (especially useful for loops)" }
+# exemple:
+for 0..2 {
+    PRE { $_ > 1 } # This is going to blow up with "Precondition failed"
+}
+
 POST { say "Asserts a postcondition at every block exit,
     after LEAVE (especially useful for loops)" }
+for 0..2 {
+    POST { $_ < 2 } # This is going to blow up with "Postcondition failed"
+}
 
 ## * Block/exceptions phasers
 sub {
@@ -1239,14 +1244,14 @@ so 'foo!' ~~ / <-[ a..z ] + [ f o ]> + /; # True (the + doesn't replace the left
 # Group: you can group parts of your regexp with `[]`.
 # These groups are *not* captured (like PCRE's `(?:)`).
 so 'abc' ~~ / a [ b ] c /; # `True`. The grouping does pretty much nothing
-so 'fooABCABCbar' ~~ / foo [ A B C ] + bar /;
+so 'foo012012bar' ~~ / foo [ '01' <[0..9]> ] + bar /;
 # The previous line returns `True`.
-# We match the "ABC" 1 or more time (the `+` was applied to the group).
+# We match the "012" 1 or more time (the `+` was applied to the group).
 
 # But this does not go far enough, because we can't actually get back what
 #  we matched.
 # Capture: We can actually *capture* the results of the regexp, using parentheses.
-so 'fooABCABCbar' ~~ / foo ( A B C ) + bar /; # `True`. (using `so` here, `$/` below)
+so 'fooABCABCbar' ~~ / foo ( 'A' <[A..Z]> 'C' ) + bar /; # `True`. (using `so` here, `$/` below)
 
 # So, starting with the grouping explanations.
 # As we said before, our `Match` object is available as `$/`: