From 8f9021a84dcfcf16ce2c4d646276e86174fa7a77 Mon Sep 17 00:00:00 2001 From: samcv Date: Tue, 18 Oct 2016 12:49:42 -0700 Subject: [PATCH] Perl6: Add many more smartmatch examples. Make the ternary operator clearer (#2472) * Explain that you cannot pass immutable values like integers to subs even if you use $n is rw. * Add myself as a contributor * Remove contributor since I am not a major contributor * Add many more smartmatch examples. Make the ternary operatory clearer and add a code example for it. Make the section for && and || have a working code example and show the output it gives * Fix assigning $a $b and $c values in the && operator section * Rename a few things so they don't conflict with variables in other parts of the code * Remove extra dashes * Move description of smartmatch type checks toward the end of that section --- perl6.html.markdown | 75 ++++++++++++++++++++++++++++++++------------- 1 file changed, 53 insertions(+), 22 deletions(-) diff --git a/perl6.html.markdown b/perl6.html.markdown index 54feeee7..a69cfe00 100644 --- a/perl6.html.markdown +++ b/perl6.html.markdown @@ -237,10 +237,15 @@ unless False { say "Quite truthy" if True; # - Ternary conditional, "?? !!" (like `x ? y : z` in some other languages) -my $a = $condition ?? $value-if-true !! $value-if-false; +# returns $value-if-true if the condition is true and $value-if-false +# if it is false. +# my $result = $value condition ?? $value-if-true !! $value-if-false; -# - `given`-`when` looks like other languages' `switch`, but much more -# powerful thanks to smart matching and thanks to Perl 6's "topic variable", $_. +my $age = 30; +say $age > 18 ?? "You are an adult" !! "You are under 18"; + +# - `given`-`when` looks like other languages' `switch`, but is much more +# powerful thanks to smart matching and Perl 6's "topic variable", $_. # # This variable contains the default argument of a block, # a loop's current iteration (unless explicitly named), etc. @@ -251,6 +256,7 @@ my $a = $condition ?? $value-if-true !! $value-if-false; # Since other Perl 6 constructs use this variable (as said before, like `for`, # blocks, etc), this means the powerful `when` is not only applicable along with # a `given`, but instead anywhere a `$_` exists. + given "foo bar" { say $_; #=> foo bar when /foo/ { # Don't worry about smart matching yet – just know `when` uses it. @@ -345,16 +351,37 @@ if long-computation() -> $result { # - `eqv` is canonical equivalence (or "deep equality") (1, 2) eqv (1, 3); -# - `~~` is smart matching +# - Smart Match Operator: `~~` +# Aliases the left hand side to $_ and then evaluates the right hand side. +# Here are some common comparison semantics: + +# String or Numeric Equality + +'Foo' ~~ 'Foo'; # True if strings are equal. +12.5 ~~ 12.50; # True if numbers are equal. + +# Regex - For matching a regular expression against the left side. +# Returns a (Match) object, which evaluates as True if regexp matches. + +my $obj = 'abc' ~~ /a/; +say $obj; # ｢a｣ +say $obj.WHAT; # (Match) + +# Hashes +'key' ~~ %hash; # True if key exists in hash + +# Type - Checks if left side "has type" (can check superclasses and roles) + +1 ~~ Int; # True + +# Smart-matching against a boolean always returns that boolean (and will warn). + +1 ~~ True; # True +False ~~ True; # True + +# # General syntax is $arg ~~ &bool-returning-function; # For a complete list of combinations, use this table: # http://perlcabal.org/syn/S03.html#Smart_matching -'a' ~~ /a/; # true if matches regexp -'key' ~~ %hash; # true if key exists in hash -$arg ~~ &bool-returning-function; # `True` if the function, passed `$arg` - # as an argument, returns `True`. -1 ~~ Int; # "has type" (check superclasses and roles) -1 ~~ True; # smart-matching against a boolean always returns that boolean - # (and will warn). # You also, of course, have `<`, `<=`, `>`, `>=`. # Their string equivalent are also avaiable : `lt`, `le`, `gt`, `ge`. @@ -395,18 +422,22 @@ my @seq = 3, 9 ... * > 95; # 3 9 15 21 27 [...] 81 87 93 99; say @numbers; #=> 0 1 2 3 4 3 9 15 21 [...] 81 87 # (only 20 values) -## * And, Or +## * And &&, Or || 3 && 4; # 4, which is Truthy. Calls `.Bool` on `4` and gets `True`. 0 || False; # False. Calls `.Bool` on `0` ## * Short-circuit (and tight) versions of the above -$a && $b && $c; # Returns the first argument that evaluates to False, - # or the last argument. -$a || $b; +# Returns the first argument that evaluates to False, or the last argument. + +my ( $a, $b, $c ) = 1, 0, 2; +$a && $b && $c; # Returns 0, the first False value + +# || Returns the first argument that evaluates to True +$b || $a; # 1 # And because you're going to want them, # you also have compound assignment operators: -$a *= 2; # multiply and assignment +$a *= 2; # multiply and assignment. Equivalent to $a = $a * 2; $b %%= 5; # divisible by and assignment @array .= sort; # calls the `sort` method and assigns the result back @@ -417,19 +448,19 @@ $b %%= 5; # divisible by and assignment ## Unpacking ! # It's the ability to "extract" arrays and keys (AKA "destructuring"). # It'll work in `my`s and in parameter lists. -my ($a, $b) = 1, 2; -say $a; #=> 1 -my ($, $, $c) = 1, 2, 3; # keep the non-interesting anonymous -say $c; #=> 3 +my ($f, $g) = 1, 2; +say $f; #=> 1 +my ($, $, $h) = 1, 2, 3; # keep the non-interesting anonymous +say $h; #=> 3 my ($head, *@tail) = 1, 2, 3; # Yes, it's the same as with "slurpy subs" my (*@small) = 1; -sub foo(@array [$fst, $snd]) { +sub unpack_array(@array [$fst, $snd]) { 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 2 3 +unpack_array(@tail); #=> My first is 2, my second is 3 ! All in all, I'm 2 3 # If you're not using the array itself, you can also keep it anonymous,