Reviving a thread from three years ago (feel free to point me to something more recent) ...
In Clojure 1.6: (class (+ 1 1.0M)) ; ==> java.math.BigDecimal (class (+ 1.0 1.0M)) ; ==> java.lang.Double So combining a BigDecimal with a Long produces a BigDecimal, but combining it with a Double produces a Double. The "demotion" to Double is implied by the statement about contagion the Clojure data structures page<http://clojure.org/data_structures#Data%20Structures-Numbers>, although nothing is said about the promotion from Long to BigDecimal: Contagion BigInts and floating point types are "contagious" across operations. That is, any integer operation involving a BigInt will result in a BigInt, and any operation involving a double or float will result in a double. To me, the fact that BigDecimal is contagious sometimes but not always, seems confusing in a way that could encourage bugs. The fact that BigInts are contagious would also lead one to assume that BigDecimals are contagious. puzzler's post in this thread explained that the rationale for making Doubles rather than BigDecimals contagious is that numeric type contagion should reflect the contagion of imprecision in calculations, which is going to happen no matter type is given to the result, once you introduce any imprecise number into the calculations, i.e. in this case, a Double. And I see that when combining a Long with a BigDecimal, imprecision is not introduced. I understand the point, but I'm not sure that I agree: If you used a Double, you knew (or should have known) that you were getting imprecision. And pmbauer's question about Floats wasn't answered. It's still true in Clojure 1.6 that Doubles are contagious over Floats: (class (+ (float 1.0) 1.0)) ; ==> java.lang.Double I think that at the very least, if BigDecimals are contagious only some of the time, it would be worth putting big warning signs in the documentation announcing this fact. (I understand, though, that Clojure documentation is a work in progress, and is lagging in some ways behind the language, as suggested by other recent threads.) -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en --- You received this message because you are subscribed to the Google Groups "Clojure" group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
