http://www.perlmonks.org?node_id=11130792


in reply to Re: [Raku] Arcane treatment of doubles and rationals
in thread [Raku] Arcane treatment of doubles and rationals

$ say 3602879701896397/36028797018963968 == 0.100000000000000006;
True


Have they changed the spec ?
> say 3602879701896397/36028797018963968 == 0.100000000000000006; False
I have:
$ raku -v Welcome to Rakudo(tm) v2021.03. Implementing the Raku(tm) programming language v6.d. Built on MoarVM version 2021.03.
If the RHS is a rational, then it's fairly easy to show that 3602879701896397/36028797018963968 != 100000000000000006/1000000000000000000.
(A/B == C/D if and only if A*D == B*C. In this case, A*D ends in zero and B*C ends in 8 so the equivalence cannot possibly hold.)

If the RHS is a double, then it's correct that 3602879701896397/36028797018963968 == 0.100000000000000006.
However, the 3 doubles assigned (respectively) the 3 values 0.100000000000000006, 0.10000000000000001 and 0.1 are all exactly the same. So we find, as expected:
> say 3602879701896397/36028797018963968 == 0.100000000000000006e0; True > say 3602879701896397/36028797018963968 == 0.10000000000000001e0; True > say 3602879701896397/36028797018963968 == 0.1e0; True
I've long been curious about the mindset that has created the rational/double arithmetic on raku, and I had thought (hoped) it might be a simple task to see how it all fits together.
Alas no, and I'm starting to see that I'm going to have to locate and work through the relevant documentation if I ever want to understand it.

Cheers,
Rob