On Wed, Nov 18, 2009 at 03:08:59AM -0800, Ron wrote: : > +Although most rational implementations normalize or "reduce" fractions : > +to their smallest representation immediately through a gcd algorithm, : > +Perl allows a rational datatype to do so lazily at need, such as : > +whenever the denominator would run out of precision, but avoid the : > +overhead otherwise. Hence, if you are adding a bunch of C<Rat>s that : > +represent, say, dollars and cents, the denominator may stay 100 the : > +entire way through. The C<.nu> and C<.de> methods will return these : > +unreduced values. You can use C<$rat.=norm> to normalize the fraction. : > +The C<.perl> method will produce a decimal number if the denominator is : > +a multiple of 10. Otherwise it will normalize and return a rational : > +literal of the form -47/3. Stringifying a rational always converts : > +to C<Num> and stringifies that, so the rational internal form is : > +somewhat hidden from the casual user, who would generally prefer : > +to see decimal notation. : : Wouldn't it be better to produce a decimal number if the denominator : equals of 2**n * 5**m for n,m unsigned int? Before displaying the : value should be "decimal-normalized" by multiplying numerator and : denominator by 2**|n-m| or 5**|n-m| depending on sign(n-m). : Otherwise adding Rats representing dollars and cents which are : immediately normalized could produce flapping between rational literal : form and decimal number form. : Aside from that the specification should be: if the denominator equals : 10**n, with n unsigned integer, .perl will produce a decimal number. : Otherwise 1/30 would produce a decimal number like 0.0333333..., which : was probably not intended.
Good catch; I thought "power" and typed "multiple". I was hesitating to extend it to require factoring for the solution, but there's actually a fast way to factor for 2's and 5's. Just shift off all the 0 bits on the bottom to take out all the 2's, and then look up the remaining number to see if it's a power of 5. So I'm inclined to make normal stringification also produce an exact decimal by default and only failover to Num if .perl would produce the 1/3 form. In the absence of an explicit format, I think exactness should trump limiting the size of the resulting string arbitrarily. Larry
