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.


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