diff options
Diffstat (limited to 'perl6.html.markdown')
| -rw-r--r-- | perl6.html.markdown | 167 |
1 files changed, 152 insertions, 15 deletions
diff --git a/perl6.html.markdown b/perl6.html.markdown index fe5b197c..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 = <a b c>; # array of words, delimited by space. +my @letters = <a b c>; # 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` @@ -700,15 +756,37 @@ try { open 'foo'; CATCH { when X::AdHoc { say "unable to open file !" } - # any other exception will be re-raised, since we don't have a `default` + # Any other exception will be re-raised, since we don't have a `default` + # Basically, if a `when` matches (or there's a `default`) marks the exception as + # "handled" so that it doesn't get re-thrown from the `CATCH`. + # You still can re-throw the exception (see below) by hand. } } # You can throw an exception using `die`: die X::AdHoc.new(payload => 'Error !'); -# TODO warn -# TODO fail -# TODO CONTROL + +# You can access the last exception with `$!` (usually used in a `CATCH` block) + +# There are also some subtelties to exceptions. Some Perl 6 subs return a `Failure`, +# which is a kind of "unthrown exception". They're not thrown until you tried to look +# at their content, unless you call `.Bool`/`.defined` on them - then they're handled. +# (the `.handled` method is `rw`, so you can mark it as `False` back yourself) +# +# You can throw a `Failure` using `fail`. Note that if the pragma `use fatal` is on, +# `fail` will throw an exception (like `die`). +fail "foo"; # We're not trying to access the value, so no problem. +try { + fail "foo"; + CATCH { + default { say "It threw because we try to get the fail's value!" } + } +} + +# There is also another kind of exception: Control exceptions. +# Those are "good" exceptions, which happen when you change your program's flow, +# using operators like `return`, `next` or `last`. +# You can "catch" those with `CONTROL` (not 100% working in Rakudo yet). ### Packages # Packages are a way to reuse code. Packages are like "namespaces", and any @@ -1246,7 +1324,7 @@ so 'abc' ~~ / a b* c /; # `True` so 'abbbbc' ~~ / a b* c /; # `True` so 'aec' ~~ / a b* c /; # `False`. "b"(s) are optional, not replaceable. -# - `**` - "Quantify It Yourself". +# - `**` - (Unbound) Quantifier # If you squint hard enough, you might understand # why exponentation is used for quantity. so 'abc' ~~ / a b ** 1 c /; # `True` (exactly one time) @@ -1255,6 +1333,27 @@ so 'abbbc' ~~ / a b ** 1..3 c /; # `True` so 'abbbbbbc' ~~ / a b ** 1..3 c /; # `False` (too much) so 'abbbbbbc' ~~ / a b ** 3..* c /; # `True` (infinite ranges are okay) +# - `<[]>` - Character classes +# Character classes are the equivalent of PCRE's `[]` classes, but +# they use a more perl6-ish syntax: +say 'fooa' ~~ / f <[ o a ]>+ /; #=> 'fooa' +# You can use ranges: +say 'aeiou' ~~ / a <[ e..w ]> /; #=> 'aeiou' +# Just like in normal regexes, if you want to use a special character, escape it +# (the last one is escaping a space) +say 'he-he !' ~~ / 'he-' <[ a..z \! \ ]> + /; #=> 'he-he !' +# You'll get a warning if you put duplicate names +# (which has the nice effect of catching the wrote quoting:) +'he he' ~~ / <[ h e ' ' ]> /; # Warns "Repeated characters found in characters class" + +# You can also negate them ... (equivalent to `[^]` in PCRE) +so 'foo' ~~ / <-[ f o ]> + /; # False + +# ... and compose them: : +so 'foo' ~~ / <[ a..z ] - [ f o ]> + /; # False (any letter except f and o) +so 'foo' ~~ / <-[ a..z ] + [ f o ]> + /; # True (no letter except f and o) +so 'foo!' ~~ / <-[ a..z ] + [ f o ]> + /; # True (the + doesn't replace the left part) + ## Grouping and capturing # Group: you can group parts of your regexp with `[]`. # These groups are *not* captured (like PCRE's `(?:)`). @@ -1282,7 +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｣ @@ -1296,15 +1395,53 @@ 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<key>` for hash access and `match[idx]` for array access) +say $/[0].list.perl; #=> (Match.new(...),).list + # We can see it's a list of Match objects. Those contain a bunch of infos: + # where the match started/ended, the "ast" (see actions later), etc. + # You'll see named capture below with grammars. ## Alternatives - the `or` of regexps # WARNING: They are DIFFERENT from PCRE regexps. so 'abc' ~~ / a [ b | y ] c /; # `True`. Either "b" or "y". so 'ayc' ~~ / a [ b | y ] c /; # `True`. Obviously enough ... +# The difference between this `|` and the one you're used to is LTM. +# LTM means "Longest Token Matching". This means that the engine will always +# try to match as much as possible in the strng +'foo' ~~ / fo | foo /; # `foo`, because it's longer. +# To decide which part is the "longest", it first splits the regex in two parts: +# The "declarative prefix" (the part that can be statically analyzed) +# and the procedural parts. +# Declarative prefixes include alternations (`|`), conjuctions (`&`), +# sub-rule calls (not yet introduced), literals, characters classes and quantifiers. +# The latter include everything else: back-references, code assertions, +# and other things that can't traditionnaly be represented by normal regexps. +# +# Then, all the alternatives are tried at once, and the longest wins. +# Exemples: +# DECLARATIVE | PROCEDURAL +/ 'foo' \d+ [ <subrule1> || <subrule2> ] /; +# DECLARATIVE (nested groups are not a problem) +/ \s* [ \w & b ] [ c | d ] /; +# However, closures and recursion (of named regexps) are procedural. +# ... There are also more complicated rules, like specificity +# (literals win over character classes) + +# Note: the first-matching `or` still exists, but is now spelled `||` +'foo' ~~ / fo || foo /; # `fo` now. + + + + ### Extra: the MAIN subroutime # The `MAIN` subroutine is called when you run a Perl 6 file directly. # It's very powerful, because Perl 6 actually parses the argument @@ -1317,7 +1454,7 @@ sub MAIN($name) { say "Hello, you !" } # t.pl <name> # And since it's a regular Perl 6 sub, you can haz multi-dispatch: -# (using a "Bool" for the named argument so that we get `--replace` +# (using a "Bool" for the named argument so that we can do `--replace` # instead of `--replace=1`) subset File of Str where *.IO.d; # convert to IO object to check the file exists |