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| -rw-r--r-- | perl6.html.markdown | 94 |
1 files changed, 94 insertions, 0 deletions
diff --git a/perl6.html.markdown b/perl6.html.markdown index b21cb1fa..e2c82a58 100644 --- a/perl6.html.markdown +++ b/perl6.html.markdown @@ -411,6 +411,7 @@ sub next-index($n) { $n + 1; } my $new-n = next-index(3); # $new-n is now 4 + # This is true for everything, except for the looping constructs (due to performance reasons): # there's no purpose in building a list if we're just going to discard all the results. # If you still want to build one, you can use the `do` prefix: (or the `gather` prefix, which we'll see later) @@ -710,6 +711,10 @@ Foo::Bar::inc; #=> 3 constant Pi = 3.14; constant $var = 1; +# And if you're wondering, yes, it can also contain infinite lists. +constant why-not = 5, 15 ... *; +say why-not[^5]; #=> 5 15 25 35 45 + ## * `state` (happens at run time, but only once) # State variables are only executed one time # (they exist in other langages such as C as `static`) @@ -782,6 +787,62 @@ sub do-db-stuff { UNDO $db.rollback; # or rollback if all hell broke loose } +### Statement prefixes +# Those act a bit like phasers: they affect the behavior of the following code. +# Though, they run in-line with the executable code, so they're in lowercase. +# (`try` and `start` are theoretically in that list, but explained somewhere else) +# Note: all of these (except start) don't need explicit brackets (`{` and `}`) for their block. + +# - `do` (that you already saw) - runs a block or a statement as a term +# You can't normally use a statement as a value (or "term"): +# +# my $value = if True { 1 } # `if` is a statement - parse error +# +# This works: +my $a = do if True { 5 } # with `do`, `if` is now a term. + +# - `once` - Makes sure a piece of code only runs once +for ^5 { once say 1 }; #=> 1 + # Only prints ... once. +# Like `state`, they're cloned per-scope +for ^5 { sub { once say 1 }() } #=> 1 1 1 1 1 + # Prints once per lexical scope + +# - `gather` - Co-routine thread +# Gather allows you to `take` several values in an array, +# much like `do`, but allows you to take any expression. +say gather for ^5 { + take $_ * 3 - 1; + take $_ * 3 + 1; +} #=> -1 1 2 4 5 7 8 10 11 13 +say join ',', gather if False { + take 1; + take 2; + take 3; +} # Doesn't print anything. + +# - `eager` - Evaluate statement eagerly (forces eager context) +# Don't try this at home: +# +# eager 1..*; # this will probably hang for a while (and might crash ...). +# +# But consider: +constant thrice = gather for ^3 { say take $_ }; # Doesn't print anything +# versus: +constant thrice = eager gather for ^3 { say take $_ }; #=> 0 1 2 3 4 + +# - `lazy` - Defer actual evaluation until value is fetched (forces lazy context) +# Not yet implemented !! + +# - `sink` - An `eager` that discards the results (forces sink context) +constant nilthingie = sink for ^3 { .say } #=> 0 1 2 +say nilthingie.perl; #=> Nil + +# - `quietly` - Supresses warnings +# Not yet implemented ! + +# - `contend` - Attempts side effects under STM +# Not yet implemented ! ### More operators thingies ! @@ -1004,4 +1065,37 @@ for <a b c> { # but the `^` makes it *not run* on the first iteration #=> b c } + +### Extra: the MAIN subroutime +# The `MAIN` subroutine is called when you run a Perl 6 file directly. +# It's very powerful, because Perl 6 actually parses the argument +# and pass them as such to the sub. It also handles named argument (`--foo`) +# and will even go as far as to autogenerate a `--help` +sub MAIN($name) { say "Hello, you !" } +# This produces: +# $ perl6 cli.pl +# Usage: +# 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` instead of `--replace=`) +subset File of Str where *.IO.d; # convert to IO object, then check the file exists + +multi MAIN('add', $key, $value, Bool :$replace) { ... } +multi MAIN('remove', $key) { ... } +multi MAIN('import', File, Str :$as) { ... } # omitting parameter name +# This produces: +# $ perl 6 cli.pl +# Usage: +# t.pl [--replace] add <key> <value> +# t.pl remove <key> +# t.pl [--as=<Str>] import (File) +# As you can see, this is *very* powerful. It even went as far as to show inline the constants. +# (the type is only displayed if 1. there's no argument name 2. it's a named argument) ``` + +If you want to go further, you can: + - Read the [Perl 6 Advent Calendar](http://perl6advent.wordpress.com/). This is probably the greatest source of Perl 6 information, snippets and such. + - Come along on `#perl6` at `irc.freenode.net`. The folks here are always helpful. + - Check the [source of Perl 6's functions and classes](https://github.com/rakudo/rakudo/tree/nom/src/core). Rakudo is mainly written in Perl 6 (with a lot of NQP, "Not Quite Perl", a Perl 6 subset easier to implement and optimize). + - Read the [Synopses](perlcabal.org/syn). They explain it from an implementor point-of-view, but it's still very interesting. |