In Scheme I can do:
#;> (numerator 1/3)
1
#;> (denominator 1/3)
3
In Clojure I can do something similar:
user=> (numerator 1/3)
1
user=> (denominator 1/3)
3
But in Scheme I can do:
#;> (numerator 0.3)
3.0
and it is not possible in Clojure:
user=> (numerator 0.3)
ClassCastException java.lang.Double cannot be cast to clojure.lang.Ratio clojure.core/numerator (core.clj:3306)
How can I convert a Double (or actually any kind of number) into a clojure.lang.Ratio?
In Scheme we have also inexact->exact what would be something like "double to ratio" in Clojure, but I can't find anything similar to it.
Ooh, I know this one!
user=> (rationalize 0.3)
3/10
user=> (numerator (rationalize 0.3))
3
But the OP points out that this doesn't work for all numbers:
user=> (numerator (rationalize 1))
ClassCastException java.lang.Long cannot be cast to clojure.lang.Ratio clojure.core/numerator (core.clj:3306)
see his Java interop workaround in his answer.
[edit] OP here:
Here is a more generic solution:
user=> (numerator (clojure.lang.Numbers/toRatio (rationalize 1)))
1
user=> (numerator (clojure.lang.Numbers/toRatio (rationalize 0.3)))
3
user=> (numerator (clojure.lang.Numbers/toRatio (rationalize 1/3)))
1