Literals & quoting

FatRat — unlimited-precision rationals

Full

A rational whose numerator and denominator grow without bound.

A FatRat is like a Rat but with no limit on the size of its denominator. Where a Rat degrades to floating point once its denominator outgrows a machine word, a FatRat stays exact however large the parts become.

Exact past the Rat limit #

say (10 ** 20).FatRat / 3 + 1;
say (1/3).FatRat.WHAT;

Output

33333333333333333334.333333
(FatRat)

The value is held exactly as a big numerator over 3; say still rounds the display to six places, but the stored value is precise.

Exactly reversible #

Because nothing is lost to floating point, operations undo cleanly — a third times three is exactly one, not 0.9999….

my $f = (1/3).FatRat;
say $f * 3;
say $f * 3 == 1;

Output

1
True

Notes #

Coerce into the type with .FatRat; arithmetic that mixes a FatRat with other numbers promotes the result to FatRat, keeping it exact.
Use it when you need exact rationals with very large or repeatedly-multiplied denominators (continued fractions, high-precision series); a plain Rat is fine for everyday decimals.
The numeric tower is Int ⊂ Rat ⊂ FatRat ⊂ Num; FatRat sits above Rat precisely because it removes the denominator-size ceiling.