Beefy Boxes and Bandwidth Generously Provided by pair Networks
XP is just a number

Re^4: One out of three ain't bad (order)

by eric256 (Parson)
on Oct 23, 2005 at 04:02 UTC ( #502285=note: print w/replies, xml ) Need Help??

in reply to Re^3: One out of three ain't bad (order)
in thread One out of three ain't bad

Why are you using sum instead of grep here? If you are summing 1 and 0 then the sum will always be the same as the grep answer. For what it's worth I woul disagree that ($_ ? 1 : 0) is clearer in anyway than !!$_. To me the !! version yells bool, while I had to read the ?: version twice before comprehension came. That might be in part because Perl6's new bool context (don't shoot me if that isn't the right wording) lets you ask for a true/false value explicity so thats what I would expext !! to do.

Eric Hodges
  • Comment on Re^4: One out of three ain't bad (order)

Replies are listed 'Best First'.
Re^5: One out of three ain't bad (order)
by Tanktalus (Canon) on Oct 23, 2005 at 15:39 UTC

    I'm using some because the parent used sum. And s/he's using sum because s/he is emulating tye's addition of booleans.

    You're right that !! screams boolean. However, that's not what is happening here. We are adding numbers here. Let me ask you what "true + false + true" is. That's just nonsensical. Programmers have been getting away with it for years because computers only deal with numbers - whether that's boolean, character, or, oddly enough, numerical. But, abstractly, it makes no sense. You can't add booleans. Boolean algebra consists of operators such as not, and, or, xor, nand, and nor. (I may have missed some - it's been a few years since I've dealt that directly with boolean algebra in the theoretical sense.) Addition, subtraction, multiplication, division - all of these are nonsensical in the boolean world. In fact, the multiplication symbol (the middle-dot, ·) was reused for the "and" operator, and the addition symbol (+) was reused for the "or" operator, IIRC (which I may not recall correctly...). And, as in mathematical algebra, the multiplication symbol is optional between terms, further reusing the sigils.

    Therefore, adding boolean values is just confusing. The answer to the question above is that "true + false + true" equals "true" (numerically: 1 || 0 || 1) - and the OP wants this to be a count of 2. Which, if my memory serves, the OP wants "a nor b nor c" Unfortunately, the nor solution doesn't scale past three.

    grep, unlike sum, uses boolean context. So the choices are to either sum numbers (using the ternary operator, for example), or to grep a list in scalar context. Adding booleans makes me question whether the author knows what s/he's doing, or is just copying what someone else is doing - whether s/he's too clever (in taking advantage of undefined behaviour) or not clever enough by half (in just copying something that works without understanding that it's undefined behaviour).

      Hehe. True enough and i didn't even see that before you posted. Thanks for clarifying. I should know better after discovering that different versions of Access use differn't values for true and false one uses 1 for true, while another uses -1.. which causes huge confusion when relying on 1 ....which as you point out I shouldn't.

      /me sets back in his chair and waits for perl6 so i can do if one(@a) == true { }

      Eric Hodges
      In fact, the multiplication symbol (the middle-dot, ) was reused for the "and" operator, and the addition symbol (+) was reused for the "or" operator, IIRC (which I may not recall correctly...).

      You recall correctly. Some people find it counterintuitive that 'plus' (+) should be used for 'or' because, in natural language, we often use 'plus' as an informal conjunction meaning 'and'. But... it makes perfect sense when you compare the boolean algebra operators with their counterparts in arithmetic...

      ABA and BA times B

      ABA or BA plus B

      So, addition is essentially boolean disjunction with the added feature of counting how many clauses are true. Having more than two values comes in handy. (Note that xor is the same as addition modulus 2.) The OP's query can be answered using only standard boolean algebra operators, of course. $x xor $y xor $z and not ($x and $y) would be one way.

      "My two cents aren't worth a dime.";

Log In?

What's my password?
Create A New User
Node Status?
node history
Node Type: note [id://502285]
and all is quiet...

How do I use this? | Other CB clients
Other Users?
Others scrutinizing the Monastery: (4)
As of 2018-02-22 22:43 GMT
Find Nodes?
    Voting Booth?
    When it is dark outside I am happiest to see ...

    Results (299 votes). Check out past polls.