diff options
| -rw-r--r-- | perl6.html.markdown | 82 |
1 files changed, 52 insertions, 30 deletions
diff --git a/perl6.html.markdown b/perl6.html.markdown index 599f207c..6cacc672 100644 --- a/perl6.html.markdown +++ b/perl6.html.markdown @@ -24,7 +24,7 @@ Meta-note : the triple pound signs are here to denote headlines, double paragrap ### Variables # In Perl 6, you declare a lexical variable using `my` - +a # Perl 6 has 4 variable types : ## - Scalars. They represent a single value. They start with a `$` @@ -39,7 +39,7 @@ my $bool = True; # `True` and `False` are Perl 6's boolean my $inverse = !$bool; # You can invert a bool with the prefix `!` operator my $forced-bool = so $str; # And you can use the prefix `so` operator which turns its operand into a Bool -## - Arrays. They represent multiple values. They start with `@` +## - Arrays. They represent multiple values. Their name start with `@`. my @array = 1, 2, 3; my @array = 'a', 'b', 'c'; @@ -51,11 +51,11 @@ say @array[2]; # Array indices start at 0 -- This is the third element say "Interpolate an array using [] : @array[]"; #=> Interpolate an array using [] : a b c ## - Hashes. Key-Value Pairs. -# Hashes are actually arrays of Pairs (`Key => Value`), "flattened" to remove duplicated keys. - +# Hashes are actually arrays of Pairs (`Key => Value`), +# except they get "flattened", removing duplicated keys. my %hash = 1 => 2, 3 => 4; -my %hash = autoquoted => "key", # keys are auto-quoted +my %hash = autoquoted => "key", # keys *can* get auto-quoted "some other" => "value", # trailing commas are okay ; my %hash = <key1 value1 key2 value2>; # you can also create a hash from an even-numbered array @@ -81,13 +81,15 @@ sub say-hello-to(Str $name) { # you can provide the type of an argument say "Hello, $name !"; } -# since you can omit parenthesis to call a function with no arguments, you need to use `&` also to capture `say-hello` +# since you can omit parenthesis to call a function with no arguments, +# you need "&" in the name to capture `say-hello` my &s = &say-hello; my &other-s = sub { say "anonymous function !" } # A sub can have a "slurpy" parameter, or "doesn't-matter-how-many" sub as-many($head, *@rest) { # the `*@` slurpy will basically "take everything else". - # Note: you can have parameters *before* (like here) a slurpy one, but not *after*. + # Note: you can have parameters *before* (like here) a slurpy one, + # but not *after*. say @rest.join(' / ') ~ " !"; } say as-many('Happy', 'Happy', 'Birthday'); #=> Happy Birthday ! @@ -124,18 +126,22 @@ sub with-named($normal-arg, :$named) { say $normal-arg + $named; } with-named(1, named => 6); #=> 7 +# There's one gotcha to be aware of, here: +# If you quote your key, Perl 6 won't be able to see it as compile time, +# and you'll have a single Pair object as a positional paramater. + with-named(2, :named(5)); #=> 7 with-named(3, :4named); #=> 7 # (special colon pair syntax for numbers, mainly useful for `:2nd` etc) -with-named(3); # warns, because we tried to use the undefined $named - # in a `+`: by default, named arguments are *optional* +with-named(3); # warns, because we tried to use the undefined $named in a `+`: + # by default, named arguments are *optional* # To make a named argument mandatory, you can use `?`'s inverse, `!` sub with-mandatory-named(:$str!) { say "$named !"; } -with-mandatory-named(str => "My String"); #=> My String +with-mandatory-named(str => "My String"); #=> My String ! with-mandatory-named; # run time error: "Required named parameter not passed" with-mandatory-named(3); # run time error: "Too many positional parameters passed" @@ -160,6 +166,9 @@ named-def; #=> 5 named-def(:10def); #=> 10 named-def(def => 15); #=> 15 +# -- Note: we're going to learn *more* on subs really soon, +# but we need to grasp a few more things to understand their real power. Ready? + ### Containers # In Perl 6, values are actually stored in "containers". # the assignment operator asks the container on the left to store the value on its right @@ -176,13 +185,14 @@ sub mutate($n is rw) { # A sub itself returns a container, which means it can be marked as rw : my $x = 42; sub mod() is rw { $x } -mod() = 52; # in this case, the parentheses are mandatory +mod() = 52; # in this case, the parentheses are mandatory (else Perl 6 thinks it's a "term") say $x; #=> 52 ### Control Flow Structures -# You don't need to put parenthesis around the condition, but that also means you always have to use brackets (`{ }`) for their body : +# You don't need to put parenthesis around the condition, +# but that also means you always have to use brackets (`{ }`) for their body : ## Conditionals @@ -204,12 +214,14 @@ say "Quite truthy" if True; my $a = $condition ?? $value-if-true !! $value-if-false; # - `given`-`when` looks like other languages `switch`, but it's much more powerful thanks to smart matching. -# given just puts its argument into `$_` (like a block), and `when` uses it using the "smart matching" operator. +# given just puts its argument into `$_` (like a block), +# and `when` uses it using the "smart matching" operator. given "foo bar" { when /foo/ { # you'll read about the smart-matching operator below -- just know `when` uses it say "Yay !"; } - when $_.chars > 50 { # smart matching anything with True gives True, so you can also put "normal" conditionals + when $_.chars > 50 { # smart matching anything with True (`$a ~~ True`) is True, + # so you can also put "normal" conditionals. say "Quite a long string !"; } default { # same as `when *` (using the Whatever Star) @@ -325,8 +337,9 @@ $a && $b && $c; # returns the first argument that evaluates to False, or the las $a || $b; ### More on subs ! +# As we said before, Perl 6 has *really* powerful subs. +# We're going to see a few more key concepts that make them better than in any other language :-). -## There's more to come, but we're going to end this paragraph with a really powerful feature: ## Unpacking ! It's the ability to "extract" arrays and keys. It'll work in `my`s and parameters. my ($a, $b) = 1, 2; say $a; #=> 1 @@ -337,7 +350,8 @@ my ($head, *@tail) = 1, 2, 3; # Yes, it's the same as with "slurpy subs" my (*@small) = 1; sub foo(@array [$fst, $snd]) { - say "My first is $fst, my second is $snd ! All in all, I'm @array[]."; # (remember the `[]` to interpolate the array) + say "My first is $fst, my second is $snd ! All in all, I'm @array[]."; + # (^ remember the `[]` to interpolate the array) } foo(@tail); #=> My first is 2, my second is 3 ! All in all, I'm 1 2 @@ -361,6 +375,8 @@ fst(1); #=> 1 fst(1, 2); # errors with "Too many positional parameters passed" # You can also destructure hashes (and classes, which you'll learn about later !) +# The syntax is basically `%hash-name (:key($variable-to-store-value-in))`. +# The hash can stay anonymous if you only need the values you extracted. sub key-of(% (:value($val), :qua($qua))) { say "Got val $val, $qua times."; } @@ -392,18 +408,19 @@ my &lambda = -> $argument { "The argument passed to this lambda is $argument" } # We can, for example, add 3 to each value of an array using map: my @arrayplus3 = map({ $_ + 3 }, @array); # $_ is the implicit argument -# a sub (`sub {}`) has different semantics than a block (`{}` or `-> {}`) : -# a block doesn't have a function context (though it can have arguments), which means that if you +# a sub (`sub {}`) has different semantics than a block (`{}` or `-> {}`): +# a block doesn't have a "function context" (though it can have arguments), which means that if you # return from it, you're going to return from the parent function, compare: sub is-in(@array, $elem) { - # this will `return` out of `is-in` sub + # this will `return` out of the `is-in` sub # once the condition evaluated to True, the loop won't be run anymore map({ return True if $_ == $elem }, @array); } sub truthy-array(@array) { - # this will produce an array of `True` and `False` : + # this will produce an array of `True` and `False`: # (you can also say `anon sub` for "anonymous subroutine") - map(sub { if $_ { return True } else { return False } }, @array); # returns the correct value, even in a `if` + map(sub { if $_ { return True } else { return False } }, @array); + # ^ the `return` only returns from the anonymous `sub` } # You can also use the "whatever star" to create an anonymous function @@ -419,7 +436,7 @@ say ((*+3)/5)(5); #=> 1.6 # you can also use the implicit argument syntax, `$^` : map({ $^a + $^b + 3 }, @array); # same as the above -# Note : those are sorted lexicographically. `{ $^b / $^a }` is like `-> $a, b { $ b / $a }` +# Note : those are sorted lexicographically. `{ $^b / $^a }` is like `-> $a, b { $b / $a }` ## Multiple Dispatch # Perl 6 can decide which variant of a `sub` to call based on the type of the arguments, @@ -501,7 +518,7 @@ sub bar { ## In Perl 6, every field is private, and named `$!attr`, but if you declare it with `$.`, ## you get a public (immutable) accessor along with it. -# (Perl 6's object model ("P6Model") is very flexible, and allows you to dynamically add methods, +# (Perl 6's object model ("SixModel") is very flexible, and allows you to dynamically add methods, # change semantics, etc -- This will not be covered here, and you should refer to the Synopsis) class A { @@ -552,9 +569,10 @@ class B is A { # inheritance uses `is` method bar { $.val * 10 } # this shadows A's `bar` } -my B $b .= new(val => 5); # When you use `my T $var`, `$var` starts off with `T` itself in it, so you can call `new` on it - # (`.=` is just the compound operator composed of the dot-call and of the assignment operator) - # +my B $b .= new(val => 5); # When you use `my T $var`, `$var` starts off with `T` itself in it, + # so you can call `new` on it. + # (`.=` is just the compound operator composed of the dot-call and of the assignment operator + # `$a .= b` is the same as `$a = $a.b`) # Also note that `BUILD` (the method called inside `new`) will set parent properties too, # so you can pass `val => 5` # $b.not-inherited; # This won't work, for reasons explained above @@ -765,7 +783,9 @@ $a ! $b ! $c; # with a list-associative `!`, this is `infix:<>` ## Create your own operators ! # Okay, you've been reading all of that, so I guess I should try to show you something exciting. -# I'll tell you a little secret (actually not): In Perl 6, all operators are actually just funny-looking subroutines. +# I'll tell you a little secret (actually not): +# In Perl 6, all operators are actually just funny-looking subroutines. + # You can declare an operator just like you declare a sub: sub prefix:<win>($winner) { # refer to the operator categories # (yes, it's the "words operator" `<>`) @@ -818,8 +838,9 @@ postcircumfix:<{ }>(%h, $key, :delete); # with great power comes great responsibility) ## Meta operators ! -# Oh boy, get ready. Get ready, because we're dwelving deep into the rabbit's hole, and you probably won't want -# to go back to other languages after reading that (I'm sure you don't want to already at that point). +# Oh boy, get ready. Get ready, because we're dwelving deep into the rabbit's hole, +# and you probably won't want to go back to other languages after reading that. +# (I'm guessing you don't want to already at that point). # - Reduce meta-operator @@ -900,7 +921,8 @@ for <test start print this stop you stopped printing start printing again stop n #=> "print this printing again" } -# you might also use a Whatever Star, which is equivalent to `True` for the left side or `False` for the right : +# you might also use a Whatever Star, +# which is equivalent to `True` for the left side or `False` for the right: for (1, 3, 60, 3, 40, 60) { .say if $_ > 50 ff *; # Once the flip-flop reached a number greater than 50, it'll never go back to `False` #=> 60 3 40 60 |