0.1 + 0.2 is exactly 0.3

In Python and JavaScript, 0.1 + 0.2 is not equal to 0.3. In Raku it is, because 0.1 is stored as a fraction.

Most programming languages cannot add 0.1 and 0.2 exactly. Raku can, and that surprises people who already know the other answer.

In Python

print(0.1 + 0.2 == 0.3)
print(0.1 + 0.2)

False
0.30000000000000004

In JavaScript

console.log(0.1 + 0.2 === 0.3);
console.log(0.1 + 0.2);

false
0.30000000000000004

In Raku

say 0.1 + 0.2 == 0.3;
say 0.1 + 0.2;

True
0.3

This is not say rounding the result for you. The sum really is three tenths.

Why

Python and JavaScript store 0.1 as a binary floating-point number. One tenth has no exact form in binary, in the same way that one third has no exact form in decimal: 0.3333… never ends. So the computer stores the nearest value it can. The small errors in 0.1 and 0.2 add up, and the sum misses 0.3 by a tiny amount.

In Raku, a number written with a decimal point, like 0.1, is a Rat, a rational number. It is stored as two integers: a numerator and a denominator. 0.1 is 1/10, 0.2 is 2/10, and their sum is 3/10, exactly. The method .nude shows the two integers; its name comes from numerator and denominator.

say 0.1.WHAT;
say 0.1.nude;
say (0.1 + 0.2).nude;

(Rat)
(1 10)
(3 10)

The same goes for division: 1/3 is kept as one third, not as 0.333333, so three of them make exactly one.

say 1/3 + 1/3 + 1/3 == 1;

True

Say it in Raku

There is nothing to fix. Decimal numbers in your program add up the way they do on paper.

When you do want a floating-point number, for speed or to get the same result as another language, write it with an exponent: e0 means “times ten to the power of zero”. Then Raku gives the same answer as Python.

say 0.1e0 + 0.2e0 == 0.3e0;
say 0.1e0 + 0.2e0;
say (0.1e0 + 0.2e0).WHAT;

False
0.30000000000000004
(Num)