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Comment by shadowfox | Hacker News Reader

This sort of distinction exists in other languages though: Java has == and equals. OCaml has = and == etc. (Not that Perl doesn't have its issues; but this is very low in that list imho)

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Ahd in Common Lisp, EQ, EQL, EQUAL, and EQUALP. See http://www.nhplace.com/kent/PS/EQUAL.html for an explanation of why.

Mistakes from other languages are still mistakes.

One could try to call them tradeoffs rather than mistakes, but then you'd have to explain why the programmer benefits from such circuitous thinking.

I don't think that one is a mistake. At least, if it's a mistake, it's not a mistake in the equals operator. PHP attempted to use one set of comparison operators and the fallout has been far worse: there have been security problems due to the semantics of PHP's == operator attempting to guess whether to perform string or numeric comparison when doing password comparisons.

The mistake, if any, is that numbers and strings are unified into one scalar type in Perl. This allows some tricks, such as being able to use sprintf to perform rounding, but it has fallout in other places in the language, such as here. Given that numbers and strings are unified, having two operators for comparison is the correct decision: it makes the semantics much simpler by having the language not guess which kind of comparison to perform.

They're not mistakes; read the article. "Equality" is not the singular, unambiguous concept that many programmers think it is.

That is not what perl and bash do. They distinguish between "comparing as strings" and "comparing as numbers". For example, the strings "03" and "3" are different, but as numbers, they are equal (and, I guess "010" is equal to "8", numerically. I didn't try, because I don't want to know)

For bash, read http://unix.stackexchange.com/questions/16109/bash-double-eq... (especially http://unix.stackexchange.com/a/120235) and weep.

For perl, see for example http://www.perlmonks.org/?node_id=276023

But in those languages, the equivalent to ($x == "foo") will return false (almost) all of the time. The poster here says that this expression is true (almost) all of the time in Perl. Why?

Because if you disable warnings, it silently coerces 'foo' to 0.

This is why disciplined (i.e. non-tiny-script-y) perl code starts off with

    use strict;
    use warnings;

just like disciplined javascript starts off with

    /* use strict */

and disciplined C code enables compiler warnings, and truly disciplined C code makes those fatal, just like in perl you can do

    use warnings FATAL => 'all';

If you don't do that, then you get the short script/one liner style behaviour where, just like sed, awk or bash, it assumes you know what you're doing. If you don't, then you should be asking the VM to help tell you when those problems exist, same as 'set -x' in bash is incredibly useful if you don't plan to add '|| exit 255;' onto the end of every command.

I've been writing perl for over ten years. I think I learned to stick "use strict; use warnings;" at the top of my scripts on day number 1. God only knows why so many other Perl programmers never learnt this.

But what is $x? Integer? String? Character? Some_Object?

How do you evaluate this, depends on the context. Wasn't that the whole point of a dynamic language anyway?

After learning Haskell, I'm not sure what the benefits of dynamic typing are anymore.

No, not at all. Type coercion is orthogonal to type safety.

Amen, brother! I call this "weak typing". But some others use weak typing to mean different things (like "unsafe typing") [1].

Javascript, PHP and Perl are weakly typed. Smalltalk, Lisp, Python, Ruby... are strong typed. But all of them are dynamic.

[1] http://en.wikipedia.org/wiki/Strong_and_weak_typing#Predicta...

I love dynamic languages with strong typing. You get most of the dev time developments, but without the inherent subtle bugs that creep in via automatic type coercion.

Those languages are far more maintainable and their communities have far more respect for practices which prevent programming errors.

I don't particularly care how many forms of equality or comparison a language has as long as the compiler or runtime is capable of telling me the particular one I'm using is probably wrong. If == can't be used with strings the damn interpreter should tell me so instead of silently and improperly coercing the arguments.

The interpreter does tell you.

    $ perl -e 'use warnings; use strict; print "content" == "foo", "\n"'
    Argument "foo" isn't numeric in numeric eq (==) at -e line 1.
    Argument "content" isn't numeric in numeric eq (==) at -e line 1.
    1

Thanks - I'll try to remember that if I ever have to touch perl again.

You should have used strict and warnings. RTFM, I know.

Btw, Java will silently compare references instead of value. Learning a language != increasing vocabulary.

Tell me about it. At least Python can make the difference between equality and identity, while a non-overriden equals() in Java actually means "is X Y?" instead of "is X equal to Y?".

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