class Backtrace

Snapshot of the dynamic call stack

class Backtrace is List { ... }

A backtrace shows the dynamic call stack, usually leading up to a point where an exception was thrown.

It is a List of Backtrace::Frame objects. Its default stringification excludes backtrace frames that are deemed unnecessary or confusing, for example routines like &die are hidden by default.

Methods

method new

proto method new(*@, *%) {*}
multi method new()

Creates a new backtrace, using its calling location as the origin of the backtrace.

method Str

multi method Str(Backtrace:D:) returns Str:D:

Returns a concise string representation of the backtrace, omitting routines marked as is hidden_from_backtrace, and at the discretion of the implementor, also some routines from the setting.

method full

multi method full(Backtrace:D:) returns Str:D:

Returns a full string representation of the backtrace, including hidden frames, compiler-specific frames and those from the setting.

Type graph

Below you should see a clickable image showing the type relations for Backtrace that links to the documentation pages for the related types. If not, try the PNG version instead.

perl6-type-graph Backtrace Backtrace List List Backtrace->List Mu Mu Any Any Any->Mu Iterable Iterable Iterable->Any Cool Cool Cool->Any Positional Positional List->Iterable List->Cool List->Positional

Methods supplied by class List

Backtrace inherits from class List, which provides the following methods:

method Bool

multi method Bool(List:D:) returns Bool:D

Returns True if the list has at least one element, and False for the empty list.

method Str

multi method Str(List:D:) returns Str:D

Stringifies the elements of the list and joins them with spaces (same as .join(' ')).

method Int

multi method Int(List:D:) return Int:D

Returns the number of elements in the list (same as .elems).

method Numeric

multi method Numeric(List:D:) return Int:D

Returns the number of elements in the list (same as .elems).

Methods supplied by role Positional

Backtrace inherits from class List, which does role Positional, which provides the following methods:

method of

method of()

Returns the type constraint for elements of the positional container. Defaults to Mu.

Methods supplied by class Cool

Backtrace inherits from class Cool, which provides the following methods:

method abs

method abs()

Coerces the invocant to Numeric and returns the absolute value (that is, a non-negative number).

method conj

method conj()

Coerces the invocant to Numeric and returns the complex conjugate (that is, the number with the sign of the imaginary part negated).

method sqrt

method sqrt()

Coerces the invocant to Numeric and returns the square root, that is, a non-negative number that, when multiplied with itself, produces the original number.

method sign

method sign()

Coerces the invocant to Numeric and returns its sign, that is, 0 if the number is 0, 1 for positive and -1 for negative values.

method rand

method rand()

Coerces the invocant to Num and returns a pseudo-random value between zero and the number.

method sin

method sin()

Coerces the invocant to Numeric, interprets it as radians, returns its sine.

method asin

method asin()

Coerces the invocant to Numeric, and returns its arc-sine in radians.

method cos

method cos()

Coerces the invocant to Numeric, interprets it as radians, returns its sine.

method acos

method acos()

Coerces the invocant to Numeric, and returns its arc-cosine in radians.

method tan

Coerces the invocant to Numeric, interprets it as radians, returns its tangens.

method atan

method atan()

Coerces the invocant to Numeric, and returns its arc-tangens in radians.

method atan2

method atan2($y = 1e0)

Coerces the invocant to Numeric, and together with its argument, returns its two-argument arc-tangens in radians.

method sec

method sec()

Coerces the invocant to Numeric, interprets it as radians, returns its secans, that is, the reciprocal of its cosine.

method asec

method asec()

Coerces the invocant to Numeric, and returns its arc-secans in radians.

method cosec

method cosec()

Coerces the invocant to Numeric, interprets it as radians, returns its cosecans, that is, the reciprocal of its sine.

method acosec

method acosec()

Coerces the invocant to Numeric, and returns its arc-cosecans in radians.

method cotan

method cotan()

Coerces the invocant to Numeric, interprets it as radians, returns its cotangens, that is, the reciprocal of its tangens.

method acotan

method acotan()

Coerces the invocant to Numeric, and returns its arc-cotangens in radians.

method sinh

method sinh()

Coerces the invocant to Numeric, and returns its Sine hyperbolicus.

method asinh

method asinh()

Coerces the invocant to Numeric, and returns its Inverse Sine hyperbolicus.

method cosh

method cosh()

Coerces the invocant to Numeric, and returns its Cosine hyperbolicus.

method acosh

method acosh()

Coerces the invocant to Numeric, and returns its Inverse Cosine hyperbolicus.

method tanh

method tanh()

Coerces the invocant to Numeric, and returns its Tangens hyperbolicus.

method atanh

method atanh()

Coerces the invocant to Numeric, and returns its Inverse tangens hyperbolicus.

method log

multi method log(Cool:D: Cool:D $base?)

Coerces the invocant to Numeric, and returns its Logarithm to base $base, or to base e (Euler's Number) if no base was supplied (Natural logarithm.

method exp

multi method exp(Cool:D: Cool:D $base?)

Coerces the invocant to Numeric, and returns $base raised to the power of this number. If no $base is supplied, e (Euler's Number) is used.

say 0.exp;      # 1
say 1.exp;      # 2.71828182845905
say 10.exp;     # 22026.4657948067

method round

multi method round(Cool:D: $unit = 1)

Coerces the invocant to Numeric, and rounds it to the unit of $unit. If $unit is 1, rounds to the nearest integer.

say 1.7.round;          # 2
say 1.07.round(0.1);    # 1.1
say 21.round(10);       # 20

method floor

multi method floor

Coerces the invocant to Numeric, and rounds it downwards to the nearest integer.

say "1.99".floor;       # 1
say "-1.9".floor;       # -2
say 0.floor;            # 0

method ceiling

multi method ceiling

Coerces the invocant to Numeric, and rounds it upwards to the nearest integer.

say "1".ceiling;        # 1
say "-0.9".ceiling;     # 0
say "42.1".ceiling;     # 43

method ord

method ord()

Coerces the invocant to Str, and returns the Unicode code point, number of the code point.

say 'a'.ord;            # 65

The inverse operation is chr.

method chr

method chr()

Coerces the invocant to Int, interprets it as a Unicode code points, and returns a string made of that code point.

say '65'.chr;       # A

The inverse operation is ord.

Mnemonic: turns an integer into a character.

method chars

method chars()

Coerces the invocant to Str, and returns the number of characters in the string. Characters should actually be grapheme clusters, though current implementation errornously count codepoints instead.

say 'møp'.chars;    # 3

method codes

method codes()

Coerces the invocant to Str, and returns the number of Unicode code points.

say 'møp'.codes;    # 3

method flip

method flip()

Coerces the invocant to Str, and returns a reversed version.

say 421.flip;       # 124

method trim

method trim()

Coerces the invocant to Str, and returns the string with both leading and trailing whitespace stripped.

my $stripped = '  abc '.trim;
say "<$stripped>";          # <abc>

method trim-leading

method trim(-leading)

Coerces the invocant to Str, and returns the string with leading whitespace stripped.

my $stripped = '  abc '.trim-leading;
say "<$stripped>";          # <abc >

method trim-trailing

method trim-trailing()

Coerces the invocant to Str, and returns the string with both leading and trailing whitespace stripped.

my $stripped = '  abc '.trim-trailing;
say "<$stripped>";          # <  abc>

method lc

method lc()

Coerces the invocant to Str, and returns it case-folded to lower case.

say "ABC".lc;       # abc

method uc

method uc()

Coerces the invocant to Str, and returns it case-folded to upper case (capital letters).

say "Abc".uc;       # ABC

method tc

method tc()

Coerces the invocant to Str, and returns it with the first letter case-folded to title case (or where not available, upper case).

say "abC".tc;       # AbC

method tclc

method tclc()

Coerces the invocant to Str, and returns it with the first letter case-folded to title case (or where not available, upper case), and the rest of the string case-folded to lower case..

say 'abC'.tclc;     # Abc

method wordcase

method wordcase(:&filter = &tclc, Mu :$where = True)

Coerces the invocant to Str, and filters each word that smart-matches against $where through the &filter. With the default filter (first character to upper case, rest to lower) and matcher (which accepts everything), this title-cases each word:

say "perl 6 programming".wordcase;      # Perl 6 Programming

With a mather:

say "have fun working on perl".wordcase(:where({ .chars > 3 }));
                                        # Have fun Working on Perl

With a customer filter too:

say "have fun working on perl".wordcase(:filter(&uc), :where({ .chars > 3 }));
                                        # HAVE fun WORKING on PERL

method chop

method chop()

Coerces the invocant to Str, and returns it with the last character removed.

say 'perl'.chop;                        # per

method chomp

method chomp()

Coerces the invocant to Str, and returns it with the last character removed, if it is a logical newline.

say 'ab'.chomp.chars;                   # 2
say "a\n".chomp.chars;                  # 1

method words

method words(Int() $limit)

Coerces the invocan to Str, and returns a list of words that make up the string (and if $limit is supplied, only the first $limit words).

say 'The quick brown fox'.words.join('|');      # The|quick|brown|fox
say 'The quick brown fox'.words(2).join('|');   # The|quick

Only whitespace counts as word boundaries

say "isn't, can't".words.join('|');             # isn't,|can't

method IO

method IO() returns IO::Path:D

Coerces the invocant to IO::Path.

.say for '.'.IO.dir;        # gives a directory listing

Methods supplied by class Any

Backtrace inherits from class Any, which provides the following methods:

method ACCEPTS

multi method ACCEPTS(Any:D: Mu $other)

Returns True if $other === self (i.e. it checks object identity).

method any

Interprets the invocant as a list and creates an any-Junction from it.

method all

Interprets the invocant as a list and creates an all-Junction from it.

method one

Interprets the invocant as a list and creates an one-Junction from it.

method none

Interprets the invocant as a list and creates an none-Junction from it.

method list

Interprets the invocant as a list, and returns that list.

method flat

Interprets the invocant as a list, flattens it, and returns that list.

say ((1, 2), (3)).elems;        # 2
say ((1, 2), (3)).flat.elems;   # 3

method eager

Interprets the invocant as a list, evaluates it eagerly, and returns that list.

method elems

Interprets the invocant as a list, and returns the number of elements in the list.

method end

Interprets the invocant as a list, and returns the last index of that list.

Methods supplied by class Mu

Backtrace inherits from class Mu, which provides the following methods:

method Str

multi method Str()   returns Str

Returns a string representation of the invocant, intended to be machine readable.

method clone

method clone(*%twiddles)

Creates a shallow clone of the invocant. If named arguments are passed to it, their values are used in every place where an attribute name matches the name of a named argument.

method new

multi method new(*%attrinit)

Default method for constructing (create + initialize) new objects of a class. This method expects only named arguments which are then used to initialize attributes with accessors of the same name.

Classes may provide their own new method to override this default.

method bless

method bless(*%attrinit) returns Mu:D

Lower-level object construction method than new.

Creates a new object of the same type as the invocant, uses the named arguments to initialize attributes, and returns the created object.

You can use this method when writing custom constructors:

class Point {
    has $.x;
    has $.y;
    multi method new($x, $y) {
        self.bless(:$x, :$y);
    }
}
my $p = Point.new(-1, 1);

(Though each time you write a custom constructor, remember that it makes subclassing harder).

method CREATE

method CREATE() returns Mu:D

Allocates a new object of the same type as the invocant, without initializing any attributes.

method print

multi method print() returns Bool:D

Prints value to $*OUT after stringification using .Str method without newline at end.

method say

multi method say() returns Bool:D

Prints value to $*OUT after stringification using .gist method with newline at end.

method ACCEPTS

multi method ACCEPTS(Mu:U: $other)

Performs a type check. Returns True if $other conforms to the invocant (which is always a type object or failure).

This is the method that is triggered on smart-matching against type objects, for example in if $var ~~ Int { ... }.

method WHICH

multi method WHICH() returns ObjAt:D

Returns an object of type ObjAt which uniquely identifies the object. Value types override this method which makes sure that two equivalent objects return the same return value from WHICH.

method WHERE

method WHERE() returns Int

Returns an Int representing the memory address of the object.

method WHY

multi method WHY()

Returns the attached Pod value. For instance,

    sub cast(Spell $s)
    #= Initiate a specified spell normally
    #= (do not use for class 7 spells)
    {
	do-raw-magic($s);
    }
    say &cast.WHY;

prints

Initiate a specified spell normally (do not use for class 7 spells)

See the documentation specification for details about attaching Pod to variables, classes, functions, methods, etc.

This documentation was generated from Backtrace.pod.