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Phasers ! and more:
Add default Add a bit on exceptions (TODO fail/warn)
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@ -116,14 +116,18 @@ say "Quite truthy" if True;
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# - Ternary conditional
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my $a = $condition ?? $value-if-true !! $value-if-false; # `??` and `!!` are like `?` and `:` in other languages'
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# - `given`-`when` looks like other languages `switch`, but it's much more powerful thanks to smart matching :
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given "foo bar" { # given just puts its argument into `$_`, and `when` uses it using the "smart matching" operator.
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when /foo/ { # you'll read about the smart-matching operator below
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# - `given`-`when` looks like other languages `switch`, but it's much more powerful thanks to smart matching.
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# given just puts its argument into `$_`, and `when` uses it using the "smart matching" operator.
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given "foo bar" {
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when /foo/ { # you'll read about the smart-matching operator below -- just know `when` uses it
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say "Yay !";
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}
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when $_.chars > 50 { # smart matching anything with True gives True, so you can also put "normal" conditionals
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say "Quite a long string !";
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}
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default { # same as `when *` (using the Whatever Star)
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say "Something else"
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}
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}
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## Looping constructs
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@ -150,6 +154,12 @@ for @array {
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say "I've got $_";
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}
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for @array {
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next if $_ == 3; # you can skip to the next iteration (like `continue` in C-like languages)
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redo if $_ == 4; # you can re-do the iteration, keeping the same topic variable (`$_`)
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last if $_ == 5; # you can also break out of a loop (like `break` in C-like languages)
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}
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# Note - the "lambda" `->` syntax isn't reserved to `for` :
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if long-computation() -> $result {
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say "The result is $result";
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@ -411,6 +421,74 @@ class Item does PrintableVal {
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# since the compiler will consider `ROLE` to be a class
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}
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### Exceptions
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# Exceptions are built on top of classes, usually in the package `X` (like `X::IO`).
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# Unlike many other languages, in Perl 6, you put the `CATCH` block *within* the block to `try`.
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# By default, a `try` has a `CATCH` block that catches any exception (`CATCH { default {} }`).
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# You can redefine it using `when`s (and `default`) to handle the exceptions you want:
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try {
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open 'foo';
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CATCH {
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when X::AdHoc { say "unable to open file !" }
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# any other exception will be re-raised, since we don't have a `default`
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}
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}
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# You can throw an exception using `die`:
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die X::AdHoc.new(payload => 'Error !');
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# TODO warn
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# TODO fail
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# TODO CONTROL
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### Phasers
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# Phasers in Perl 6 are blocks that happen at determined points of time in your program
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# When the program is compiled, when a for loop runs, when you leave a block, when
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# an exception gets thrown ... (`CATCH` is actually a phaser !)
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# Some of them can be used for their return values, some of them can't
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# (those that can have a "[*]" in the beginning of their explanation text).
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# Let's have a look !
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## * Compile-time phasers
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BEGIN { say "[*] Runs at compile time, as soon as possible, only once" }
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CHECK { say "[*] Runs at compile time, instead as late as possible, only once" }
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## * Run-time phasers
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INIT { say "[*] Runs at run time, as soon as possible, only once" }
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END { say "Runs at run time, as late as possible, only once" }
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## * Block phasers
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ENTER { say "[*] Runs everytime you enter a block, repeats on loop blocks" }
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LEAVE { say "Runs everytime you leave a block, even when an exception happened. Repeats on loop blocks." }
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PRE { say "Asserts a precondition at every block entry, before ENTER (especially useful for loops)" }
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POST { say "Asserts a postcondition at every block exit, after LEAVE (especially useful for loops)" }
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## * Block/exceptions phasers
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sub {
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KEEP { say "Runs when you exit a block successfully (without throwing an exception)" }
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UNDO { say "Runs when you exit a block unsuccessfully (by throwing an exception)" }
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}
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## * Loop phasers
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for ^5 {
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FIRST { say "[*] The first time the loop is run, before ENTER" }
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NEXT { say "At loop continuation time, before LEAVE" }
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LAST { say "At loop termination time, after LEAVE" }
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}
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## * Role/class phasers
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COMPOSE { "When a role is composed into a class. /!\ NOT YET IMPLEMENTED /!\" }
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# They allow for cute trick or clever code ...:
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say "This code took " ~ (time - CHECK time) ~ "s to run";
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# ... or clever organization:
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sub do-db-stuff {
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ENTER $db.start-transaction; # create a new transaction everytime we enter the sub
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KEEP $db.commit; # commit the transaction if all went well
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UNDO $db.rollback; # or rollback if all hell broke loose
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}
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### More operators thingies !
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