Thanks - the raku and gist methods were what I needed to locate and comprehend. 
$ raku -e 'my $r = 3602879701896397/36028797018963968; say $r.raku; sa
+y $r.raku == $r;'
0.1000000000000000055511151231257827021181583404541015625
True

[download]

This is much more like what I expected of the raku language.
I'm surprised that the gist method sacrifices accuracy so readily. Even 1/128 does not render the exact value, providing 0.007813 instead of 0.0078125.
But that's a matter of choice - I now see nothing buggy happening there.

As regards converting a double to its exact rational representation, this is quite simple in perl: 
$ perl -le 'printf "%.800g\n", 0.1'
0.1000000000000000055511151231257827021181583404541015625
$

[download]
Is the same thing also as straightforward in raku ?
I tried: 
$ raku -e 'printf "%.800g\n", 0.1e0'
NaN
$

[download]
I've read documentation stating that raku's printf() expects that the last argument must be a string.

Cheers,
Rob

In reply to Re^3: [Raku] Arcane treatment of doubles and rationals by syphilis
in thread [Raku] Arcane treatment of doubles and rationals by syphilis

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