Re: [isabelle] Problem with pretty printing rationals
I just encountered the following problem. When writing a pretty printer
for rational numbers the standard function I would like to write is:
show_rat (Fract a b) = (if b = 1 then show_int a else show_int a @ ''/''
@ show_int b)"
However, since Fract is a only a code_datatype and not a datatype,
Isabelle refused this function definition. (And it must refuse, since
Fract 1 2 = Fract 2 4, but show_rat .. = 1/2 != 2/4 = show_rat ..
Hence, show_rat is not a function.)
Right. This cannot work.
Are there for example
functions like "get_numerator" and "get_denominator" which return unique
results independent of whether using (Fract 1 2) or (Fract 2 4) which I
overlooked in Rational.thy?
There aren't, but it seems that they should be there, so contributions
are welcome (probably a function that returns (int * int) is best). It
can be defined using THE.
This archive was generated by a fusion of
Pipermail (Mailman edition) and