Re: undef == 0?

It actually makes perfect sense to me, in that undef and 0 both evaluate to "false" and "false" equals "false." I've programmed Fortran for many years (my first editor was an IBM-029 card punch 8=)); Fortran actually has a dedicated logical operators, .EQV. and .NEQV. to compare Boolean values. Part of the reason for this that some older Fortrans would do something like "x == y" (actually, X .EQ. Y) without any kind of cast: the compiler would just generate the instructions to compare the actual bit sequences. And Fortran's concept of "true" vs "false" can be a trifle confusing. Of course, one could now digress into why -0 != 0, but one shouldn't.

emc

Information about American English usage here and here.

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Comment on Re: undef == 0?

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Re^2: undef == 0? by stu42j (Sexton) on Oct 25, 2007 at 05:09 UTC
`1` and `2` are both true in boolean context so does that mean that `1 == 2`?	[reply] [d/l] [select]
Re^3: undef == 0? by codeacrobat (Chaplain) on Oct 25, 2007 at 06:21 UTC
== forces scalar context. Both 1 and 2 are treated as decimal integers. Obviously they are not the same. `print+qq(\L@{[ref\&@]}@{['@'x7^'!#2/"!4']});`	[reply] [d/l]
Re^4: undef == 0? by stu42j (Sexton) on Oct 25, 2007 at 19:37 UTC
Uhm, yeah. That was a rhetorical question type thing in response to swampyankee's suggestion that since undef and 0 are both false then it logically follows that undef == 0 should also be true. I was just giving an example where boolean equality is not equivalent to numeric equality.	[reply]
Re^3: undef == 0? by mrpeabody (Friar) on Oct 25, 2007 at 16:12 UTC
No, what it means is that `is_true(1) == is_true(2)`, where is_true is something like `sub { $_[0] ? 1 : 0 }`	[reply] [d/l] [select]
Re^3: undef == 0? by swampyankee (Parson) on Oct 26, 2007 at 00:08 UTC
It does mean that `1 && 2` evaluates to true. And, were Perl to have Fortran-style logical comparison operators (.EQV. and .NEQV.; this gives me an idea for an Acme module...), `1 eqv 2` would evaluate to true. Every language has its little corners which may not be that well thought out; `undef& == 0` evaluating to true may be one of them (0⁰ evaluating to 1 is probably another). It is consistent, and arguably reasonable, behavior, although it's just as sensible, and arguably more reasonable, to have `undef` behave like NaN and not be comparable to anything, even itself (`NaN == NaN` and `NaN != NaN` are both false in most languages). emc Information about American English usage here and here. Any Northeastern US area jobs? I'm currently unemployed.	[reply]


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