Rational literals

Decimals and fractions are exact rationals (Rat), not floating point.

A number written with a decimal point, or produced by dividing two integers, is a Rat — an exact rational held as a numerator/denominator pair. This is why Raku does not suffer the classic floating-point surprise.

Division yields a Rat #

say 1/3;
say (1/3).^name;

0.333333
Rat

The value is stored exactly as 1/3; only its display is rounded to six decimal places by say. To see the exact value, ask for it:

say (1/3).raku;
say (3/4).nude;

<1/3>
(3 4)

.nude returns the "nude" numerator and denominator as a list; .raku shows the literal form that would reconstruct the value.

Decimal literals are exact #

Because decimals are rationals, sums that famously misbehave in floating point are exact here.

say 0.1 + 0.2;

0.3

Comparison with the same thing in floating point #

To opt into floating point, write a number in scientific notation (1e0) or coerce with .Num. See Number literals once written.

Notes #

• A Rat keeps its denominator in a machine word. When a denominator would grow past that, the value degrades to a Num (floating point) rather than slowing to a crawl — a deliberate performance trade also made by Rakudo.
• Equality is exact: 0.1 + 0.2 == 0.3 is True, unlike in most languages.