referenced part

multi to-base-alphabet ( Real $num, @alphabet, :$precision = -15 ) is export {
    temp @__base-any-digits = @alphabet;
    temp $threshold = +@alphabet;

    say $threshold;
    return convert-arbitrary-base( $num, $threshold, :$precision ); # 137
}

test output

Cannot resolve caller convert-arbitrary-base(0.1, 4516, :precision(-15)); none of these signatures match:
    (Int $num, Int $radix where { ... })
    (Real $num, Int $radix where { ... }, :$precision)
  in sub to-base-alphabet at /home/altreus/src/Base-Any/lib/Base/Any.pm6 (Base::Any) line 137
  in block <unit> at t/01-basic.t line 66