class Label

Tagged location in the source code
class Label {}

Labels are used in Raku to tag loops so that you can specify the specific one you want to jump to with statements such as last. You can use it to jump out of loops and get to outer ones, instead of just exiting the current loop or going to the previous statement.

USERS:          # the label
for @users -> $u {
    for $u.pets -> $pet {
        # usage of a label
        next USERS if $pet.barks;
    }
    say "None of {$u}'s pets barks";
}
say USERS.^name;        # OUTPUT: «Label␤»

Those labels are objects of type Label, as shown in the last statement. Labels can be used in any loop construct, as long as they appear right before the loop statement.

my $x = 0;
my $y = 0;
my $t = '';
A: while $x++ < 2 {
    $t ~= "A$x";
    B: while $y++ < 2 {
        $t ~= "B$y";
        redo A if $y++ == 1;
        last A
    }
}
say $t; # OUTPUT: «A1B1A1A2␤»

Putting them on the line before the loop or the same line is optional. Labels must follow the syntax of ordinary identifiers, although traditionally we will use the latin alphabet in uppercase so that they stand out in the source. You can use, however, other alphabets like here:

駱駝道: while True {
      say 駱駝道.name;
      last 駱駝道;
    }  # OUTPUT: «駱駝道␤»

Methods

method name

Not terribly useful, returns the name of the defined label:

A: while True {
      say A.name; # OUTPUT: «A␤»
      last A;
    }

method file

Returns the file the label is defined in.

method line

Returns the line where the label has been defined.

method Str

Converts to a string including the name, file and line it's been defined in.

method next

method next(Label:)

Begin the next iteration of the loop associated with the label.

MY-LABEL:
    for 1..10 {
        next MY-LABEL if $_ < 5;
        print "$_ ";
    }
# OUTPUT: «5 6 7 8 9 10 »

method redo

method redo(Label:)

Repeat the same iteration of the loop associated with the label.

my $has-repeated = False;
MY-LABEL:
    for 1..10 {
        print "$_ ";
        if $_ == 5 {
            LEAVE $has-repeated = True;
            redo MY-LABEL unless $has-repeated;
        }
    }
# OUTPUT: «1 2 3 4 5 5 6 7 8 9 10 »

method last

method last(Label:)

Terminate the execution of the loop associated with the label.

MY-LABEL:
    for 1..10 {
        last MY-LABEL if $_ > 5;
        print "$_ ";
    }
# OUTPUT: «1 2 3 4 5 »

See Also

class int

Native integer

class Allomorph

Dual value number and string

class Any

Thing/object

class AST

Abstract representation of a piece of source code

class atomicint

Integer (native storage at the platform's atomic operation size)

class Block

Code object with its own lexical scope

class CallFrame

Captures the current frame state

class Code

Code object

class Collation

Encapsulates instructions about how strings should be sorted

class Compiler

Information related to the compiler that is being used

class Complex

Complex number

class ComplexStr

Dual value complex number and string

class Cool

Object that can be treated as both a string and number

class CurrentThreadScheduler

Scheduler that synchronously executes code on the current thread

class Date

Calendar date

class DateTime

Calendar date with time

class Distribution::Hash

Distribution::Hash

class Distribution::Locally

Distribution::Locally

class Distribution::Path

Distribution::Path

class Distribution::Resource

Every one of the resources installed with a distribution

class Duration

Length of time

class Encoding::Registry

Management of available encodings

class FatRat

Rational number (arbitrary-precision)

class ForeignCode

Rakudo-specific class that wraps around code in other languages (generally NQP)

class Format

Convert values to a string given a format specification

class Formatter

Produce Callable for given format specification

class HyperSeq

An object for performing batches of work in parallel with ordered output

class HyperWhatever

Placeholder for multiple unspecified values/arguments

class Instant

Specific moment in time

class Int

Integer (arbitrary-precision)

class IntStr

Dual value integer and string

class Junction

Logical superposition of values

class Lock::Async

A non-blocking, non-re-entrant, mutual exclusion lock

class Macro

Compile-time routine

class Method

Member function

class Mu

The root of the Raku type hierarchy.

class Nil

Absence of a value or a benign failure

class Num

Floating-point number

role Numeric

Number or object that can act as a number

class NumStr

Dual value floating-point number and string

class ObjAt

Unique identification for an object

class Parameter

Element of a Signature

class Perl

Perl related information

class Proxy

Item container with custom storage and retrieval

class RaceSeq

Performs batches of work in parallel without respecting original order.

class Raku

Raku related information

package RakuAST

Namespace for holding RakuAST related classes

class RakuAST::Doc::Block

Contains the information of a RakuDoc block

class RakuAST::Doc::Declarator

Contains the declarator docs of a RakuAST object

class RakuAST::Doc::Markup

Contains the information about RakuDoc markup

class RakuAST::Doc::Paragraph

Contains the information about a RakuDoc paragraph

class Rat

Rational number (limited-precision)

class RatStr

Dual value rational number and string

class Routine

Code object with its own lexical scope and return handling

class Routine::WrapHandle

Holds all information needed to unwrap a wrapped routine.

class Scalar

A mostly transparent container used for indirections

class Signature

Parameter list pattern

class Str

String of characters

class StrDistance

Contains the result of a string transformation.

class Sub

Subroutine

class Submethod

Member function that is not inherited by subclasses

class Telemetry

Collect performance state for analysis

class Telemetry::Instrument::Thread

Instrument for collecting Thread data

class Telemetry::Instrument::ThreadPool

Instrument for collecting ThreadPoolScheduler data

class Telemetry::Instrument::Usage

Instrument for collecting getrusage data

class Telemetry::Period

Performance data over a period

class Telemetry::Sampler

Telemetry instrument pod

Subset UInt

Unsigned integer (arbitrary-precision)

class ValueObjAt

Unique identification for value types

class Variable

Object representation of a variable for use in traits

class Version

Module version descriptor

class Whatever

Placeholder for the value of an unspecified argument

class WhateverCode

Code object constructed by Whatever-priming

The Camelia image is copyright 2009 by Larry Wall. "Raku" is trademark of the Yet Another Society. All rights reserved.