From type/Rational

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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␤