Assignment Versus Equality

Steven D'Aprano steve at pearwood.info
Sun Jun 26 09:21:35 EDT 2016


On Sun, 26 Jun 2016 08:48 pm, BartC wrote:

> On 26/06/2016 08:36, Lawrence D’Oliveiro wrote:
>> One of Python’s few mistakes was that it copied the C convention of using
>> “=” for assignment and “==” for equality comparison.
> 
> One of C's many mistakes. Unfortunately C has been very influential.
> 
> However, why couldn't Python have used "=" both for assignment, and for
> equality? Since I understand assignment ops can't appear in expressions.

Personally, I think that even if there is no *syntactical* ambiguity between
assignment and equality, programming languages should still use different
operators for them. I must admit that my first love is still Pascal's :=
for assignment and = for equality, but C's = for assignment and == for
equality it *almost* as good.

(It loses a mark because absolute beginners confuse the assignment = for the
= in mathematics, which is just different enough to cause confusion.)

But the BASIC style = for both assignment and equality is just begging for
confusion. Even though = is not ambiguous given BASIC's rules, it can still
be ambiguous to beginners who haven't yet digested those rules and made
them second nature.

And even experts don't always work with complete statements. Here is a
snippet of BASIC code:

X = Y

Is it an assignment or an equality comparison? Without seeing the context,
it is impossible to tell:

10 X = Y + 1
20 IF X = Y GOTO 50


Now obviously BASIC was a very popular and successful language, for many
years, despite that flaw. But I wouldn't repeat it in a new language.


>> It should have copied the old convention from Algol-like languages
>> (including Pascal), where “:=” was assignment, so “=” could keep a
>> meaning closer to its mathematical usage.
> 
> (I think Fortran and PL/I also used "=" for assignment. Both were more
> commercially successful than Algol or Pascal.)

Fortran 77 used .EQ. for equality. I'm not sure about PL/I.

I'm also not sure I'd agree about the commercial success. Fortran certainly
has been extremely popular, albeit almost entirely in numerical computing.
But PL/I has virtually disappeared from the face of the earth, while Pascal
still has a small but dedicated community based on FreePascal, GNU Pascal,
and Delphi.

(Of the three, FreePascal and Delphi appear to still be getting regular
releases.)




-- 
Steven
“Cheer up,” they said, “things could be worse.” So I cheered up, and sure
enough, things got worse.



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