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Why Does “=” Mean Assignment?

hillelwayne.com

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Re: Why Does “=” Mean Assignment?

#121

Post by ben509 »

v_lisivka wrote: post #100
cup-of-tea wrote: post #80

It isn't just mathematically unsound, it's the cause of many errors, especially in C. Certainly a "million dollar mistake". A classic way to guard against accidental use of assignment in logic statements is to write it "backwards", i.e.: if (2 == x) {...} Since (2 = x) won't compile, while (x = 2) will not only compile but might appear to work for a very long time.

It's better to use -Wall -Werror options for C compiler.

Agreed, fix the tools, not the person. Really, any source you have control over should have all error checking possible turned on and breaking immediately, _especially_ with C derivatives.

Re: Why Does “=” Mean Assignment?

#122

Post by ken »

EdwardCoffin wrote: post #95
ken wrote: post #16

I don't understand the LISP line at all. I would have said "LET", "SET", and "EQUAL" (since it's talking about numbers). Is there something I'm missing? EDIT: It's since been changed to "let", "set", "equal" (but still lower-case).

I don't understand it either. I suspect the author does not know Lisp, and badly misunderstood an explanation from someone who does. I think that Lisp doesn't even fit well into that table, since putting LET in the first column would implicitly bring in declaration as well, much of the time SET in the second column would be misleading since mutation is so often done implicitly by a looping construct like DO, DOLIST,…

It's not a perfect correspondence, but I think the point is simply to show that back in the 1950's, there was no consensus yet on how assignment ought to look.

It just happens that there was no consensus yet on how it should work, yet, either!

Then again, neither of the last 2 (modern) programming languages I've used have had FORTRAN/ALGOL-style assignment semantics, so I think the jury's still out.

Re: Why Does “=” Mean Assignment?

#123

Post by neaden »

jfoutz wrote: post #79
abakus wrote: post #15

The length of symbols should roughly be negatively correlated with its frequency. Since in procedural language, assignment is a much more common operation than equality check, it is reasonable to favor "=" over ":=" or even "<-".

also, there's no hand balance on either of the composite symbols. := is my right pinky, <- is different fingers, but bottom and top row. neither exactly flows from the fingertips.

I don't think that is a big issue. Just bind it to something else. In RStudio by default <- is bound to alt and -.

Re: Why Does “=” Mean Assignment?

#124

Post by [deleted] »

abakus wrote: post #15

The length of symbols should roughly be negatively correlated with its frequency. Since in procedural language, assignment is a much more common operation than equality check, it is reasonable to favor "=" over ":=" or even "<-".

[deleted]

Re: Why Does “=” Mean Assignment?

#125

Post by kolpa »

Jtsummers wrote: post #98
mortdeus wrote: post #43

because in math it means assignment. y = mx+b That is an assignment. There is also a math symbol that specifically designates equivalence.

It should be noted that in mathematics equivalence and equality are not the same thing. Letting ~ represent an equivalence relation on a set X: Equivalence relations have specific properties: x ~ x holds for all x in X x ~ y => y ~ x for all x, y in X x ~ y /\ y ~ z => x ~ z, for all x, y, z in X However, they do not have to be equal , merely equivalent by whatever our relationship requires (though they may be equal)…

Equality doesn't exist in mathematics.

http://www.math.harvard.edu/~mazur/preprints/when_is_one.pdf

The punchline:

> In appropriate deference to the manifold ways an object can be presented to us, objects need only be given up to unique isomorphism, this being an enlightened view of what it means for one thing to be equal to some other thing.

Re: Why Does “=” Mean Assignment?

#126

Post by lloeki »

russellbeattie wrote: post #41

I've been programming professionally for 25 years using mostly C inspired languages, and I will still regularly write "if(foo = bar)" on a daily basis and not notice until there's an error. It's easily the most common syntax error I write, followed closely by using commas in my for-loop as apparently it looks like a function to my fingers: "for(x=0, x<10, x++)"

There is a Ruby idiom[0] that I find quite useful (esp. combined with a linter such as Rubocop), leveraging optional parens as a marker of intentional assignment:

  # bad
  if v = array.grep(/foo/)
    do_something(v)
    # some code
  end

  # good
  if (v = array.grep(/foo/))
    do_something(v)
    # some code
  end
Caught a number of nasty bugs that way.

[0]: https://github.com/bbatsov/ruby-style-guide#safe-assignment-...

Re: Why Does “=” Mean Assignment?

#127

Post by derefr »

rdtsc wrote: post #13

Another interesting way to think about it is as "match". That is try to match the stuff on the right with the stuff on the left. Take Erlang for example: 1> X = 1. 1 2> X = 2. ** exception error: no match of right hand side value 2 Notice variables are immutable (not just values themselves). Once X becomes 1, it can only match with 1 after that. You might think this is silly or annoying, why not just allow reassignme…

Also valid in Erlang:

    2 = X.

    {ok, Y} = X = foo().
Oh, and here's a fun one:

    1> {X, X} = {1, 1}.
    {1, 1}.
    2> {Y, Y} = {1, 2}.
    ** exception error: no match of right hand side value {1,2}
If you're wondering what the use of that is, here's an Erlang "drop all occurrences of an element X from a list" function. (Prerequisite knowledge for this: Erlang functions have several clause-heads; which one is executed on each call depends on which one is able to successfully bind to—i.e. = with—the arguments.)

    drop(X, List) -> drop(X, List, []).

    drop(X, [], Acc) -> lists:reverse(Acc);
    drop(X, [X|Rest], Acc) -> drop(X, Rest, Acc);
    drop(X, [Y|Rest], Acc) -> drop(X, Rest, [Y|Acc]).
In other words—first, set up an accumulator. Then, go through the list, and if X can bind in both positions, skip the element; otherwise (i.e. if Y != X) then shift Y into the accumulator. At the end, reverse the accumulator (because you were shifting.)

Re: Why Does “=” Mean Assignment?

#128

Post by bllguo »

nfoz wrote: post #40
jghn wrote: post #10

Earlier quoted context omitted.

There’s also <-, most commonly seen in R but draws it’s heritage from the APL keyboard

Fun fact, R also has -> (assign to the RHS instead of LHS), and "super-assignment" >, and also can use = sometimes too (and I think has different semantics). Yay R.

I write R daily and have always used = for convenience. I can count on 0 hands how many times that has affected me. <<- has its uses though!

Re: Why Does “=” Mean Assignment?

#129

Post by [deleted] »

dkrich wrote: post #108

I always liked DHH's take on these sorts of arguments (paraphrasing): who the hell cares? Once you know the purpose of the '=' how often do you make mistakes reading or writing code? Whereas Java is all about protecting developers from themselves, Ruby (for example) let's you get away without variable type declaration because at the end of the day, how often do you not know whether a particular variable is a string o…

[deleted]

Re: Why Does “=” Mean Assignment?

#130

Post by munk-a »

danans wrote: post #86

The Go language brings back the ":=" to mean declare and assign, while inferring type. a := 5 You can also equivalently do var a = 5 I almost never use the latter within functions (only at module scope). I believe the former is forbidden except within functions.

I'm not a big fan of this decision by golang, with the frequency of multi-assignment happening in common code make this awkward. Specifically:

var a = 5 a, b := 2, 3

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