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Re^3: Definition of numerically equal and rationale for 'you' == 'me'

by eyepopslikeamosquito (Canon)
on Mar 02, 2012 at 11:01 UTC ( #957439=note: print w/ replies, xml ) Need Help??


in reply to Re^2: Definition of numerically equal and rationale for 'you' == 'me'
in thread Definition of numerically equal and rationale for 'you' == 'me'

Yes, overloading + to mean either string concatenation or numeric addition is a language design blunder IMHO. I'm often saddened by how many language designers were seduced by this unfortunate misfeature. It explains why, for instance, you so often need ugly explicit coercion via the int function in Python and the to_i method in Ruby.

The elegant dividend that Perl derives from its lack of operator ambiguity is clearly and tastefully described in Modern Perl in the "Numeric, String, and Boolean Context" section on page eight:

In exchange for not having to declare (or at least track) explicitly what type of data a variable contains or a function produces, Perl offers specific type contexts that tell the compiler how to treat a given value during an operation ...

The eq operator treats its operands as strings by enforcing string context on them. The == operator imposes numeric context ...

Perl will do its best to coerce values to the proper type depending on the operators you use. Be sure to use the proper operator for the type of context you want.


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Re^4: Definition of numerically equal and rationale for 'you' == 'me'
by BrowserUk (Pope) on Mar 02, 2012 at 11:50 UTC
    The elegant dividend that Perl derives from its lack of operator ambiguity

    Hm. If only that notion had been carried through to other operators like the bitwise boolean operators where it is all to frequent that you need to enforce the context by explicit coercions.

    Not a big criticism, but it still catches me out occasionally.


    With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
    Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
    "Science is about questioning the status quo. Questioning authority".
    In the absence of evidence, opinion is indistinguishable from prejudice.

    The start of some sanity?

      Fully agreed. Other places where the context model has not been applied consistently:

      • The reverse operator does either string or list reversal depending on the calling context. Doesn't fit the pattern.
      • infix x does either string or list repetition, not by imposing context or by being sensitive to the outer context, but by introspecting the left-hand side. WRONG.

      Perl 6 has addressed those points, thought it took quite some time for some of them.

        Just read S03: Changes to Perl operators. Impressive consistency improvements. I like the new x (string multiply) versus xx (list multiply) distinction. I suppose the vast number of operators that Perl supports, compared to other languages, is made possible by sigils; that is, languages without sigils couldn't so easily use x or xx as an operator. BTW, I was surprised to learn that the string multiply operator is commutative in Python (that is, "X"*3 and 3*"X" both produce "XXX"), which looks a bit odd to me (you learn these things playing golf you see ;-).

        I also revisited the lovingly crafted Periodic Table of the Operators -- which clarifies why Perl is sometimes referred to as an "operator-oriented language".

      Hm. If only that notion had been carried through to other operators...

      Indeed. It works so well with most of the operators that it stands out so strongly when it doesn't work... such as the smartmatch operator.

        such as the smartmatch operator.

        I've never used that in real code. Nor given/when for that matter.

        I've tried to use both a few times for the sake of using them, and found that the reality didn't fit with my expectations, to the point where even reading the documentation over and over, I couldn't work out why I got the results I did. As such, neither have ever made it into my working vocabulary, despite that I know they are there.

        Extending Perl requires far more than just implementing a few specific behaviours. It seems to me that you really need Mr Wall's particular brain -- and considerable time -- to see the full impact of such changes.


        With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
        Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
        "Science is about questioning the status quo. Questioning authority".
        In the absence of evidence, opinion is indistinguishable from prejudice.

        The start of some sanity?

Re^4: Definition of numerically equal and rationale for 'you' == 'me'
by JavaFan (Canon) on Mar 03, 2012 at 00:31 UTC
    The elegant dividend that Perl derives from its lack of operator ambiguity
    Really? Can you describe what &, |, ++ and <> do, without taking the value of their operands into account?
    Yes, overloading + to mean either string concatenation or numeric addition is a language design blunder IMHO. I'm often saddened by how many language designers were seduced by this unfortunate misfeature.
    I don't call it a misfeature. It's a design decision whether you allow multiple dispatch or not. There are pro and cons, and judgement should be made in context of the entire language. If your typing system is different, multiple dispatch makes more sense (perl6 will have multiple dispatch, although I don't know whether it will have it for build in operators). Perl5 doesn't have much of it, but do note the mentioned operators. And it allows operators to be overloaded. If I want to make + to concatenate strings, I can, quite simply:
    use 5.010; use overload '""' => sub {${$_[0]}}, '+' => sub {bless\do{my$o=${$_[$_[2]]}.$_[1-$_[2]]}}; BEGIN {overload::constant q => sub {bless \do {my $v = $_[0]}}} my $x = "Hello"; my $y = "world"; my $z = "" + uc $x; say $x + ", " + $y; say $z + $z; __END__ Hello, world HELLOHELLO
    (Implementation not complete)

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