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Message from discussion == is not transitive?
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Patrick Houk  
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 More options Oct 5 2012, 10:42 am
From: Patrick Houk <path...@gmail.com>
Date: Fri, 5 Oct 2012 07:42:44 -0700 (PDT)
Local: Fri, Oct 5 2012 10:42 am
Subject: Re: == is not transitive?
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I was bitten by this a year ago and posted here:
http://groups.google.com/group/clojure/browse_frm/thread/9091ad790fc9...

My workaround is to call BigDecimal#stripTrailingZeros before passing
it to code that might compare it to some other number.

user> (== 1 (.stripTrailingZeros 1.0M))
true

However, there is an edge case:

user> (== 0 (.stripTrailingZeros 0.0M))
false

Which is due to this Java bug:
http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6480539

So I use a function like the following instead of bigdec to parse
BigDecimals.

(defn parse-stripped-bigdec [^String value-str]
  ;; Note that bigdec uses reflection (at least in Clojure 1.2.1)
  (let [n (java.math.BigDecimal. value-str)]
    (if (zero? n) 0M (.stripTrailingZeros n))))

Be aware that stripping the zeros changes how the BigDecimal is
formatted by #toString.

user> (str (parse-stripped-bigdec "10"))
"1E+1"

So, I have a special case for BigDecimal that calls #toPlainString in
the places where I do not want exponential format.

user> (.toPlainString (parse-stripped-bigdec "10"))
"10"

I hope that helps.
- Pat

On Oct 4, 8:39 pm, Ben Wolfson <wolf...@gmail.com> wrote:

> user> [(== 0 0.0) (== 0.0 0.0M) (== 0.0M 0)]
> [true true false]
> user> [(== 0 0.0 0.0M) (== 0 0.0M 0.0) (== 0.0 0 0.0M) (== 0.0 0.0M 0)
> (== 0.0M 0.0 0) (== 0.0M 0 0.0)]
> [true false false false true false]

> --
> Ben Wolfson
> "Human kind has used its intelligence to vary the flavour of drinks,
> which may be sweet, aromatic, fermented or spirit-based. ... Family
> and social life also offer numerous other occasions to consume drinks
> for pleasure." [Larousse, "Drink" entry]


 
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