role Rational

Number stored as numerator and denominator

role Rational[::NuT, ::DeTdoes Real { ... }

Rational is the common role for numbers that are stored as pairs of numerator and denominator. It is parameterized by the types of the numerator (NuT) and denominator (DeT). By default, these are Int, but other types of Rational are possible by using a different parameterization. In addition, Rational objects are immutable throughout their life.

class Positive does Rational[UInt{};
my Positive $one-third =,3);
say $one-third;                         # OUTPUT: «0.333333␤» 
my Positive $fail,3);  # OUTPUT: «Type check failed in binding to parameter 'nu'; expected UInt but got Int (-2)␤»

Please note that, since DeT is by default equal to NuT, in this case both are instantiated to UInt. Built into Raku are Rat and FatRat, which both do the Rational role.


method new

method new(NuT:D $numeratorDeT:D $denominator --> Rational:D)

Creates a new rational object from numerator and denominator, which it normalizes to the lowest terms. The $denominator can be zero, in which case the numerator is normalized to -1, 0, or 1 depending on whether the original is negative, zero, or positive, respectively.

method Bool

Defined as:

multi method Bool(Rational:D: --> Bool:D)

Returns False if numerator is 0, otherwise returns True. This applies for <0/0> zero-denominator Rational as well, despite ?<0/0>.Num being True.

method Bridge

Defined as:

method Bridge()

Returns the number, converted to Num.

method Int

Defined as:

method Int(Rational:D: --> Int:D)

Coerces the invocant to Int by truncating non-whole portion of the represented number, if any. If the denominator is zero, will fail with X::Numeric::DivideByZero.

method Num

Defined as:

method Num(Rational:D: --> Num:D)

Coerces the invocant to Num by dividing numerator by denominator. If denominator is 0, returns Inf, -Inf, or NaN, based on whether numerator is a positive number, negative number, or 0, respectively.

method ceiling

Defined as:

method ceiling(Rational:D: --> Int:D)

Return the smallest integer not less than the invocant. If denominator is zero, fails with X::Numeric::DivideByZero.

method floor

Defined as:

method floor(Rational:D: --> Int:D)

Return the largest integer not greater than the invocant. If denominator is zero, fails with X::Numeric::DivideByZero.

method isNaN

method isNaN(Rational:D: --> Bool:D)

Tests whether the invocant's Num value is a NaN, an acronym for Not available Number. That is both its numerator and denominator are zero.

method numerator

method numerator(Rational:D: --> NuT:D)

Returns the numerator.

method denominator

method denominator(Rational:D: --> DeT:D)

Returns the denominator.

method nude

method nude(Rational:D: --> Positional)

Returns a list of the numerator and denominator.

method norm

method norm(Rational:D: --> Rational:D)

DEPRECATED as of 6.d. The method is no longer needed, because as of 6.d language version, it's required for Rational type to be normalized on creation.

Returns a normalized Rational object, i.e. with positive denominator, and numerator and denominator coprime. The denominator can also by zero, but using it in any operation or a conversion to string will result in an exception.

use v6.c;
my Rational $by-zero = 3/0;
say $by-zero.norm.raku# OUTPUT: «<1/0>␤» 
say $by-zero# OUTPUT: «Attempt to divide by zero when coercing Rational to Str␤ 

method base-repeating

method base-repeating(Rational:D: Int:D() $base = 10)

Returns a list of two strings that, when concatenated, represent the number in base $base. The second element is the one that repeats. For example:

my ($non-rep$repeating= (19/3).base-repeating(10);
say $non-rep;                               # OUTPUT: «6.␤» 
say $repeating;                             # OUTPUT: «3␤» 
printf '%s(%s)'$non-rep$repeating;      # OUTPUT: «6.(3)»

19/3 is 6.333333... with the 3 repeating indefinitely.

If no repetition occurs, the second string is empty:

say (5/2).base-repeating(10).raku;          # OUTPUT: «("2.5", "")␤»

The precision for determining the repeating group is limited to 1000 characters, above that, the second string is ???.

$base defaults to 10.

method Range

Returns a Range object that represents the range of values supported.

Type Graph

Type relations for Rational
perl6-type-graph Rational Rational Real Real Rational->Real Numeric Numeric Real->Numeric Mu Mu Any Any Any->Mu Cool Cool Cool->Any FatRat FatRat FatRat->Rational FatRat->Cool Rat Rat Rat->Rational Rat->Cool Stringy Stringy Str Str Str->Cool Str->Stringy RatStr RatStr RatStr->Rat RatStr->Str

Expand above chart

Routines supplied by role Real

Rational does role Real, which provides the following routines:

(Real) method Bridge

Defined as:

method Bridge(Real:D:)

Default implementation coerces the invocant to Num and that's the behavior of this method in core Real types. This method primarily exist to make it easy to implement custom Real types by users, with the Bridge method returning one of the core Real types (NOT necessarily a Num) that best represent the custom Real type. In turn, this lets all the core operators and methods obtain a usable value they can work with.

As an example, we can implement a custom Temperature type. It has a unit of measure and the value, which are given during instantiation. We can implement custom operators or conversion methods that work with this type. When it comes to regular mathematical operators, however, we can simply use the .Bridge method to convert the Temperature to Kelvin expressed in one of the core numeric types:

class Temperature is Real {
    has Str:D  $.unit  is required where any <K F C>;
    has Real:D $.value is required;
    method new ($value:$unit = 'K'{ self.bless :$value :$unit }
    # Note: implementing .new() that handles $value of type Temperature is left as an exercise 
    method Bridge {
        when $!unit eq 'F' { ($!value + 459.67) × 5/9 }
        when $!unit eq 'C' {  $!value + 273.15 }
    method gist { self.Str }
    method Str  { "$!value degrees $!unit" }
sub postfix:<> { $^value:unit<C> }
sub postfix:<> { $^value:unit<F> }
sub postfix:<K> { $^value:unit<K> }
my $human := 36.6℃;
my $book  := 451℉;
my $sun   := 5778K;
say $human;                # OUTPUT: «36.6 degrees C␤» 
say $human + $book + $sun# OUTPUT: «6593.677777777778␤» 
say 123+ 456K;           # OUTPUT: «579␤»

As we can see from the last two lines of the output, the type of the bridged result is not forced to be any particular core type. It is a Rat, when we instantiated Temperature with a Rat or when conversion was involved, and it is an Int when we instantiated Temperature with an Int.

(Real) method Complex

method Complex(Real:D: --> Complex:D)

Converts the number to a Complex with the number converted to a Num as its real part and 0e0 as the imaginary part.

(Real) method Int

method Int(Real:D:)

Calls the Bridge method on the invocant and then the Int method on its return value.

(Real) method Rat

method Rat(Real:D: Real $epsilon = 1e-6)

Calls the Bridge method on the invocant and then the Rat method on its return value with the $epsilon argument.

(Real) method Real

Defined as:

multi method Real(Real:D: --> Real:D)
multi method Real(Real:U: --> Real:D)

The :D variant simply returns the invocant. The :U variant issues a warning about using an uninitialized value in numeric context and then returns

(Real) method Str

multi method Str(Real:D:)

Calls the Bridge method on the invocant and then the Str method on its return value.

(Real) method Num

method Num(Real:D:)

Calls the Bridge method on the invocant and then the Num method on its return value.

(Real) routine rand

sub term:<rand> (--> Num:D)
method rand(Real:D: --> Real:D)

Returns a pseudo-random number between zero (inclusive) and the number (non-inclusive). The Bridge method is used to coerce the Real to a numeric that supports rand method.

The term form returns a pseudo-random Num between 0e0 (inclusive) and 1e0 (non-inclusive.)

(Real) method sign

method sign(Real:D:)

Returns -1 if the number is negative, 0 if it is zero and 1 otherwise.

(Real) method round

method round(Real:D: $scale = 1)

Rounds the number to scale $scale. If $scale is 1, rounds to an integer. If scale is 0.1, rounds to one digit after the radix point (period or comma), etc.

(Real) method floor

method floor(Real:D: --> Int:D)

Return the largest integer not greater than the number.

(Real) method ceiling

method ceiling(Real:D: --> Int:D)

Returns the smallest integer not less than the number.

(Real) method truncate

method truncate(Real:D: --> Int:D)

Rounds the number towards zero.

(Real) method polymod

method polymod(Real:D: +@mods)

Returns the remainders after applying sequentially all divisors in the @mods argument; the last element of the array will be the last remainder.

say (1e8+1).polymod(10 xx 8);  # OUTPUT: «(1 0 0 0 0 0 0 0 1)␤»

10 xx 8 is simply an array with eight number 10s; the first division by 10 will return 1 as a remainder, while the rest, up to the last, will return 0. With 8 divisors, as above, the result will have one more elements, in this case for the last remainder.

(Real) method base

method base(Real:D: Int:D $base where 2..36$digits? --> Str:D)

Converts the number to a string, using $base as base. For $base larger than ten, capital Latin letters are used.

255.base(16);            # 'FF'

The optional $digits argument asks for that many digits of fraction (which may not be negative). If omitted, a reasonable default is chosen based on type. For Int this default is 0. For Num, the default is 8. For Rational, the number of places is scaled to the size of the denominator, with a minimum of 6.

A special value of Whatever (*) can be given as $digits, which functions the same as when $digits is not specified for all Real types except the Rationals. For Rationals, the Whatever indicates that you wish all of the possible digits of the fractional part, but use caution: since there's no detection of repeating fractional parts (the algorithm will eventually stop after generating 2**63 digits).

The final digit produced is always rounded.

say pi.base(103);      # OUTPUT: «3.142␤» 
say (1/128).base(10*); # OUTPUT: «0.0078125␤» 
say (1/100).base(10*); # OUTPUT: «0.01␤» 
say (1/3)  .base(10*); # WRONG: endlessly repeating fractional part

For reverse operation, see parse-base

Routines supplied by role Numeric

Rational does role Numeric, which provides the following routines:

(Numeric) method Numeric

Defined as:

multi method Numeric(Numeric:D: --> Numeric:D)
multi method Numeric(Numeric:U: --> Numeric:D)

The :D variant simply returns the invocant. The :U variant issues a warning about using an uninitialized value in numeric context and then returns

(Numeric) method narrow

method narrow(Numeric:D --> Numeric:D)

Returns the number converted to the narrowest type that can hold it without loss of precision.

say (4.0 + 0i).narrow.raku;     # OUTPUT: «4␤» 
say (4.0 + 0i).narrow.^name;    # OUTPUT: «Int␤»

(Numeric) method ACCEPTS

multi method ACCEPTS(Numeric:D: $other)

Returns True if $other can be coerced to Numeric and is numerically equal to the invocant (or both evaluate to NaN).

(Numeric) routine log

multi sub    log(Numeric:DNumeric $base = e --> Numeric:D)
multi method log(Numeric:D: Numeric $base = e --> Numeric:D)

Calculates the logarithm to base $base. Defaults to the natural logarithm. Returns NaN if $base is negative. Throws an exception if $base is 1.

(Numeric) routine log10

multi sub    log10(Numeric:D  --> Numeric:D)
multi method log10(Numeric:D: --> Numeric:D)

Calculates the logarithm to base 10. Returns NaN for negative arguments and -Inf for 0.

(Numeric) routine log2

multi sub    log2(Numeric:D)
multi method log2(Numeric:D:)

Calculates the logarithm to base 2. Returns NaN for negative arguments and -Inf for 0.

(Numeric) routine exp

multi sub    exp(Numeric:DNumeric:D $base = e --> Numeric:D)
multi method exp(Numeric:D: Numeric:D $base = e --> Numeric:D)

Returns $base to the power of the number, or e to the power of the number if called without a second argument.

(Numeric) method roots

multi method roots(Numeric:D: Int:D $n --> Positional)

Returns a list of the $n complex roots, which evaluate to the original number when raised to the $nth power.

(Numeric) routine abs

multi sub    abs(Numeric:D  --> Real:D)
multi method abs(Numeric:D: --> Real:D)

Returns the absolute value of the number.

(Numeric) routine sqrt

multi sub    sqrt(Numeric:D --> Numeric:D)
multi method sqrt(Numeric:D --> Numeric:D)

Returns a square root of the number. For real numbers the positive square root is returned.

On negative real numbers, sqrt returns NaN rather than a complex number, in order to not confuse people who are not familiar with complex arithmetic. If you want to calculate complex square roots, coerce to Complex first, or use the roots method.

(Numeric) method conj

multi method conj(Numeric:D --> Numeric:D)

Returns the complex conjugate of the number. Returns the number itself for real numbers.

(Numeric) method Bool

multi method Bool(Numeric:D:)

Returns False if the number is equivalent to zero, and True otherwise.

(Numeric) method succ

method succ(Numeric:D:)

Returns the number incremented by one (successor).

(Numeric) method pred

method pred(Numeric:D:)

Returns the number decremented by one (predecessor).