From 160c82684721b62e3369a912542a5f045d286d9c Mon Sep 17 00:00:00 2001 From: Nami-Doc Date: Sat, 27 Sep 2014 21:57:10 +0200 Subject: [PATCH] Capturing captures, and numbering them also, multi-indexing in arrays also, labeled loops (draft) also, arrays vs $() vs parcel vs ... (@moritz++) --- perl6.html.markdown | 86 +++++++++++++++++++++++++++++++++++++++------ 1 file changed, 76 insertions(+), 10 deletions(-) diff --git a/perl6.html.markdown b/perl6.html.markdown index d12b99ae..7afcc930 100644 --- a/perl6.html.markdown +++ b/perl6.html.markdown @@ -46,18 +46,36 @@ 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. Their name start with `@`. +## * Lists. They represent multiple values. Their name start with `@`. -my @array = 1, 2, 3; my @array = 'a', 'b', 'c'; # equivalent to : -my @array = ; # array of words, delimited by space. +my @letters = ; # array of words, delimited by space. # Similar to perl5's qw, or Ruby's %w. +my @array = 1, 2, 3; 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 +#=> Interpolate an array using [] : 1 2 3 + +@array[0] = -1; # Assign a new value to an array index +@array[0, 1] = 5, 6; # Assign multiple values + +my @keys = 0, 2; +@array[@keys] = @letters; # Assign using an array +say @array; #=> a 2 b + +# There are two more kinds of lists: Parcel and Arrays. +# Parcels are immutable lists (you can't modify a list that's not assigned). +# This is a parcel: +(1, 2, 3); # Not assigned to anything. Changing an element would provoke an error +# This is a list: +my @a = (1, 2, 3); # Assigned to `@a`. Changing elements is okay! + +# Lists flatten (in list context). You'll see below how to apply item context +# or use arrays to have real nested lists. + ## * Hashes. Key-Value Pairs. # Hashes are actually arrays of Pairs (`Key => Value`), @@ -303,6 +321,37 @@ if long-computation() -> $result { say "The result is $result"; } +## Loops can also have a label, and be jumped to through these. +OUTER: while 1 { + say "hey"; + while 1 { + OUTER.last; # All the control keywords must be called on the label itself + } +} + +# Now that you've seen how to traverse a list, you need to be aware of something: +# List context (@) flattens. If you traverse nested lists, you'll actually be traversing a +# shallow list (except if some sub-list were put in item context ($)). +for 1, 2, (3, (4, ((5)))) { + say "Got $_."; +} #=> Got 1. Got 2. Got 3. Got 4. Got 5. + +# ... However: (forcing item context with `$`) +for 1, 2, $(3, 4) { + say "Got $_."; +} #=> Got 1. Got 2. Got 3 4. + +# Note that the last one actually joined 3 and 4. +# While `$(...)` will apply item to context to just about anything, you can also create +# an array using `[]`: +for [1, 2, 3, 4] { + say "Got $_."; +} #=> Got 1 2 3 4. + +# The other difference between `$()` and `[]` is that `[]` always returns a mutable Array +# whereas `$()` will return a Parcel when given a Parcel. + + ### Operators ## Since Perl languages are very much operator-based languages @@ -359,9 +408,9 @@ $arg ~~ &bool-returning-function; # `True` if the function, passed `$arg` # This also works as a shortcut for `0..^N`: ^10; # means 0..^10 -# This also allows us to demonstrate that Perl 6 has lazy arrays, +# This also allows us to demonstrate that Perl 6 has lazy/infinite arrays, # using the Whatever Star: -my @array = 1..*; # 1 to Infinite ! +my @array = 1..*; # 1 to Infinite ! `1..Inf` is the same. say @array[^10]; # you can pass arrays as subscripts and it'll return # an array of results. This will print # "1 2 3 4 5 6 7 8 9 10" (and not run out of memory !) @@ -372,6 +421,13 @@ say @array[^10]; # you can pass arrays as subscripts and it'll return # Perl 6 will be forced to try and evaluate the whole array (to print it), # so you'll end with an infinite loop. +# You can use that in most places you'd expect, even assigning to an array +my @numbers = ^20; +@numbers[5..*] = 3, 9 ... * > 90; # The right hand side could be infinite as well. + # (but not both, as this would be an infinite loop) +say @numbers; #=> 3 9 15 21 27 [...] 81 87 + + ## * And, Or 3 && 4; # 4, which is Truthy. Calls `.Bool` on `4` and gets `True`. 0 || False; # False. Calls `.Bool` on `0` @@ -1325,7 +1381,7 @@ say $0; # The same as above. # You might be wondering why it's an array, and the answer is simple: # Some capture (indexed using `$0`, `$/[0]` or a named one) will be an array # IFF it can have more than one element -# (so, with `*`, `+` and any `**`, but not with `?`). +# (so, with `*`, `+` and `**` (whatever the operands), but not with `?`). # Let's use examples to see that: so 'fooABCbar' ~~ / foo ( A B C )? bar /; # `True` say $/[0]; #=> ｢ABC｣ @@ -1339,16 +1395,26 @@ say $0.WHAT; #=> (Array) # A specific quantifier will always capture an Array, # may it be a range or a specific value (even 1). -# If you're wondering how the captures are numbered, here's an explanation: -# (TODO use graphs from s05) +# The captures are indexed per nesting. This means a group in a group will be nested +# under its parent group: `$/[0][0]`, for this code: +'hello-~-world' ~~ / ( 'hello' ( <[ \- \~ ]> + ) ) 'world' /; +say $/[0].Str; #=> hello~ +say $/[0][0].Str; #=> ~ +# This stems from a very simple fact: `$/` does not contain strings, integers or arrays, +# it only contains match objects. These contain the `.list`, `.hash` and `.Str` methods. +# (but you can also just use `match` for hash access and `match[idx]` for array access) +say $/[0].list.perl; #=> (Match.new(...),).list + # We can see it's a list of Match objects. Those contain a bunch of infos: + # where the match started/ended, the "ast" (see actions later), etc. + # You'll see named capture below with grammars. ## Alternatives - the `or` of regexps # WARNING: They are DIFFERENT from PCRE regexps. so 'abc' ~~ / a [ b | y ] c /; # `True`. Either "b" or "y". so 'ayc' ~~ / a [ b | y ] c /; # `True`. Obviously enough ... -# The difference between this `|` and the one you're probably used to is LTM. +# The difference between this `|` and the one you're used to is LTM. # LTM means "Longest Token Matching". This means that the engine will always # try to match as much as possible in the strng 'foo' ~~ / fo | foo /; # `foo`, because it's longer.