C
Csaba Henk
(FYI: the phenomena described in the sequel were seen produced by the following
ruby instances: a vanilla 1.8.1, a Debianish 1.8.2 and a cvs snapshot
from the 10th of May, identifying itself as 1.9.0.)
require 'set'
#the empty set:
Set[]
=> #<Set: {}>
#the singleton of the empty set:
Set[ [Set[]] ]
=> #<Set: {[#<Set: {}>]}>
#if sets were extensional as God ordered, this would give the same, but...
Set[ [Set[], Set[]] ]
=> #<Set: {[#<Set: {}>, #<Set: {}>]}>
#and also...
Set[Set[]].member? Set[]
=> false
[Set[], Set[]].uniq
=> [#<Set: {}>, #<Set: {}>]
Set[ [Set[]] ] - Set[ [Set[]] ]
=> #<Set: {[#<Set: {}>]}>
#anyway...
Set[] == Set[]
=> true
Set[ [Set[]] ] == Set[ [Set[]] ]
=> false
(Set.new behaves the same way as Set[])
Now I don't see what's the purpose of having a set class which is not
extensional (ie., two sets behave as the same one in all respect if their
elements are the same). But, given it's non-extensional, why isn't it
consequently non-extensional ("Set[] == Set[]" evaluates in an extensional
manner, that is, to "true")? And how does Array#uniq work? -- by what rule
does it dispose elements if not by getting "true" by a "==" comparison with
an other member of the array?
--
Csaba
"There's more to life, than books, you know but not much more..."
[The Smiths]
***
If you want to send me a mail, see it in the mailto link at
http://www.renyi.hu/~ekho/egyelore.html
ruby instances: a vanilla 1.8.1, a Debianish 1.8.2 and a cvs snapshot
from the 10th of May, identifying itself as 1.9.0.)
require 'set'
#the empty set:
Set[]
=> #<Set: {}>
#the singleton of the empty set:
Set[ [Set[]] ]
=> #<Set: {[#<Set: {}>]}>
#if sets were extensional as God ordered, this would give the same, but...
Set[ [Set[], Set[]] ]
=> #<Set: {[#<Set: {}>, #<Set: {}>]}>
#and also...
Set[Set[]].member? Set[]
=> false
[Set[], Set[]].uniq
=> [#<Set: {}>, #<Set: {}>]
Set[ [Set[]] ] - Set[ [Set[]] ]
=> #<Set: {[#<Set: {}>]}>
#anyway...
Set[] == Set[]
=> true
Set[ [Set[]] ] == Set[ [Set[]] ]
=> false
(Set.new behaves the same way as Set[])
Now I don't see what's the purpose of having a set class which is not
extensional (ie., two sets behave as the same one in all respect if their
elements are the same). But, given it's non-extensional, why isn't it
consequently non-extensional ("Set[] == Set[]" evaluates in an extensional
manner, that is, to "true")? And how does Array#uniq work? -- by what rule
does it dispose elements if not by getting "true" by a "==" comparison with
an other member of the array?
--
Csaba
"There's more to life, than books, you know but not much more..."
[The Smiths]
***
If you want to send me a mail, see it in the mailto link at
http://www.renyi.hu/~ekho/egyelore.html