Re: == is not transitive?
On Friday, October 5, 2012 7:17:50 PM UTC+2, Ben wrote: > > I'm not sure what you mean by this. Transitivity means that for all x, > y, and z, (Fxy & Fyz) => Fxz. But there are values of x, y, and z for > which that does not hold. > Yeah, sorry. What I meant was that == is only commutative if you pass it two arguments as of right now. -- 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
Re: == is not transitive?
On Fri, Oct 5, 2012 at 2:08 AM, Jean Niklas L'orange wrote: > > On Friday, October 5, 2012 2:39:05 AM UTC+2, Ben wrote: >> >> user> [(== 0 0.0) (== 0.0 0.0M) (== 0.0M 0)] >> [true true false] > > When passing two arguments to ==, == will be transitive. I'm not sure what you mean by this. Transitivity means that for all x, y, and z, (Fxy & Fyz) => Fxz. But there are values of x, y, and z for which that does not hold. -- 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] -- 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
Re: == is not transitive?
I was bitten by this a year ago and posted here: http://groups.google.com/group/clojure/browse_frm/thread/9091ad790fc96b24 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 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] -- 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
Re: == is not transitive?
On Fri, Oct 5, 2012 at 11:08 AM, Jean Niklas L'orange wrote: > > > On Friday, October 5, 2012 2:39:05 AM UTC+2, Ben wrote: >> >> user> [(== 0 0.0) (== 0.0 0.0M) (== 0.0M 0)] >> [true true false] > > > When passing two arguments to ==, == will be transitive. > >> >> 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] > > > This is more of a problem with number equality, not the transitivity of ==. > (== x1 x2 x3 ... xn) can be rewritten as (and (== x1 x2) (== x2 x3) ... (== > xn-1 xn)). > > So if you compare (== x y z), then if x = y, then the result of (== x z) and > (== y z) should be equivalent, considering the numbers are, well, numbers. > > I believe the issue lies within the bigdec-parsing, which seems to have two > zeroes: (== 0M 0.0M) returns false, and their hashcode (0 and 1, > respectively) are different. Yea, I think this is the peculiar definition of BigDecimal.equals() biting us here. http://docs.oracle.com/javase/1.4.2/docs/api/java/math/BigDecimal.html # Note: care should be exercised if BigDecimals are to be used as keys in a # SortedMap or elements in a SortedSet, as BigDecimal's natural ordering is # inconsistent with equals. See Comparable, SortedMap or SortedSet for more # information. equals(): # Compares this BigDecimal with the specified Object for equality. Unlike # compareTo, this method considers two BigDecimals equal only if they are # equal in *value* and *scale* (thus 2.0 is not equal to 2.00 when compared by # this method) -- 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
Re: == is not transitive?
On Friday, October 5, 2012 2:39:05 AM UTC+2, Ben wrote: > > user> [(== 0 0.0) (== 0.0 0.0M) (== 0.0M 0)] > [true true false] > When passing two arguments to ==, == will be transitive. > 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] > This is more of a problem with number equality, not the transitivity of ==. (== x1 x2 x3 ... xn) can be rewritten as (and (== x1 x2) (== x2 x3) ... (== xn-1 xn)). So if you compare (== x y z), then if x = y, then the result of (== x z) and (== y z) should be equivalent, considering the numbers are, well, numbers. I believe the issue lies within the bigdec-parsing, which seems to have two zeroes: (== 0M 0.0M) returns false, and their hashcode (0 and 1, respectively) are different. -- 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
Re: == is not transitive?
The only reason for this that I can think of is incomplete rules for casting numbers. On Thursday, 4 October 2012 20:39:05 UTC-4, Ben 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] > -- 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
== is not transitive?
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] -- 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
