On Friday, 2 August 2013 12:28:51 UTC+8, CGAT wrote:

>   My understanding of == is that it is intended to establish numerical 
> equivalence
>   across types. But I think that basic contract fails with BigDecimal. For 
> instance,
>
>   (== 1M 1.0M) ; => false
>
>   because the scale properties of these numbers are different. So then of 
> course:
>
>   [(== 1 1N 1.0) (== 1 1N 1.0 1M) (== 1 1N 1.0 1.0M) (== 1 1.0 1N 1.0M)]
>     ; => [true true true false]
>   and
>   [(== 1.0M 1.0) (== 1.0 1) (== 1 1N) (== 1N 1.0M)] 
>     ; => [true true true false]
>   
>   I find your lack of transitivity (and commutativity) ... disturbing.
>
>   The issue is that there are two notions of equality for BigDecimal,
>   equals and compareTo, where equals compares value *and* scale while
>   compareTo compares numerically.
>   
>   The other numeric types use equals for equivalence, quite reasonably.
>   But in class BigDecimalOps in clojure/lang/Numbers.java, I propose
>   that
>
>     public boolean equiv(Number x, Number y){
>       return toBigDecimal(x).equals(toBigDecimal(y));
>     }
>
>   should be
>      
>     public boolean equiv(Number x, Number y){
>       return toBigDecimal(x).compareTo(toBigDecimal(y)) == 0;
>     }


Ouch, is that really what Numbers.equiv is doing? 

No wonder some of our idiomatic numerical code is so slow - a coercion to 
BigDecimal is really expensive!

It really needs instanceof checks and branches to handle the different 
cases efficiently. I'll have a go at a ticket/patch that addresses this.

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