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Dennis Ritchie on the priorities of && || vs. == etc. (1982)

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Re: Dennis Ritchie on the priorities of && || vs. == etc. (1982)

#161

Post by nathan_douglas »

teo_zero wrote: post #135

Please note that, despite the misleading title, TFA is about the precedence of bitwise operators & and | with respect to the comparison operators (== and all the others). In particular it was asked to Ritchie why the former are weaker than the latter in C, a rule generally considered a mistake because it makes it impossible to write common expressions like if (addr & mask == 0) without adding extra parentheses: if ((…

To be fair, Dennis says:

>The priorities of && || vs. == etc. came about in the following way.

I think it takes some serious concentration to tease out that he is indeed trying to explain what you indicated. Either that, or my brain is just thoroughly cooked.

I'm not arguing with you -- I think you're absolutely right -- but man, Dennis made it hard on us here

Re: Dennis Ritchie on the priorities of && || vs. == etc. (1982)

#162

Post by wruza »

userbinator wrote: post #107
thomasahle wrote: post #75

Earlier quoted context omitted.

I think most people agree "a*x**b + c" is more clear than "(a*(x**b))+c". Or "a+b+c+d" is more clear than "a+(b+(c+d))". Why are we happy to avoid parentheses for these operations but not for && and ||? Probably because we are all really used to the precedences for + and *. So at the end of the day, what's more clear depends on How familiar the engineers working on your code are with a given set of operators.

Parentheses need to be matched. That adds cognitive overhead. It's especially frustrating when you find the closing parenthesis and then realise it wasn't even necessary. IMHO it's on a similar level as "== true" "== false" and variations thereof --- absolutely redundant and unnecessary, and shows a lack of knowledge. The same "explicit is better than implicit" mantra is often repeated to justify the latter, but if y…

I got little scars from knowing precedences and then switching languages. I also got them from short-testing booleans that later turned into T|boolean. And all these clean just_p’s incrementally evolved into !just_p ? !un_q : t’s. Because I was flying through a mass-change after a day and had no mental capacity to repack the meaning of the previous expression and retain the context of a changeset.

Crystallized syntax is clear, but also extremely fragile, if you take humans into account. We have limits. Everything pushes us to these limits. Any complexity spike that overlaps with secondary complexity or fatigue is above our limits. That’s where we make mistakes.

Re: Dennis Ritchie on the priorities of && || vs. == etc. (1982)

#163

Post by teo_zero »

User23 wrote: post #159
teo_zero wrote: post #132

Earlier quoted context omitted.

Really? Do you think equivalence should be weaker than && and || so that you would write if ((a==0) && (b==0)) instead of if (a==0 && b==0)

I think equivalence and equality should different operators. 2==x should be a syntax error, because equivalence compares Boolean expressions (and possibly their extensions depending on the language). Equality should be checked with the customary sign, and assignment should be some visually asymmetric operator like :=. As you say, Equality should bind more strongly than the Boolean typed operations, including conjunct…

Sorry, I can't follow your reasoning. Probably I'm missing some basic vocabulary, because I don't appreciate the difference between equivalence and equality. Are we still talking about comparison operators?

Re: Dennis Ritchie on the priorities of && || vs. == etc. (1982)

#164

Post by pi-e-sigma »

wruza wrote: post #160
pi-e-sigma wrote: post #62

Earlier quoted context omitted.

Ada is such an underrated language. The lack of its adoption is a testament to the old adage that technologies don't thrive or die on their technical merits.

I remember reading a discussion on it in a year around <= 2000 and it was a general consensus that Ada’s printed standard is too heavy to move around, let alone implement. Military/corporate-ish affinity didn’t help either.

Compare C++ and Ada. C++ standard is an order of magnitude bigger and more complex and yet C++ is thriving. So Ada's failure definitively is not due to the language complexity. C++ has been supported heavily by the corporate, too. Biggest C++ champion was Microsoft, after all.

Re: Dennis Ritchie on the priorities of && || vs. == etc. (1982)

#165

Post by CamperBob2 »

o11c wrote: post #8
Sohcahtoa82 wrote: post #2

I don't even know the priority between && and ||. If I'm using both, I use parentheses just so it's more explicit. "a && b || c" should flag a linter, IMO, with "(a && b) || c" or "a && (b || c)" being required.

Convert them to arithmetic. If you ignore the casting, a && b is just a * b a || b is just a + b Now you remember the precedence between them (except in broken languages, of which the only notable one is shell).

No. Then I have to think about it.

I have (gently) jumped on peoples' cases for not using parentheses in expressions involving these operators, and will continue to do so, thanks.

Re: Dennis Ritchie on the priorities of && || vs. == etc. (1982)

#166

Post by MaxBarraclough »

wruza wrote: post #160
pi-e-sigma wrote: post #62

Earlier quoted context omitted.

Ada is such an underrated language. The lack of its adoption is a testament to the old adage that technologies don't thrive or die on their technical merits.

I remember reading a discussion on it in a year around <= 2000 and it was a general consensus that Ada’s printed standard is too heavy to move around, let alone implement. Military/corporate-ish affinity didn’t help either.

I see pi-e-sigma beat me to it, but:

C++ is at least as complicated as Ada, both in terms of using the language and in terms of writing a compiler for it.

C++ also sees plenty of use in military applications. The F-35's 141 page C++ coding standard is publicly available, for instance.

https://www.stroustrup.com/JSF-AV-rules.pdf

Re: Dennis Ritchie on the priorities of && || vs. == etc. (1982)

#167

Post by smcameron »

teo_zero wrote: post #135

Please note that, despite the misleading title, TFA is about the precedence of bitwise operators & and | with respect to the comparison operators (== and all the others). In particular it was asked to Ritchie why the former are weaker than the latter in C, a rule generally considered a mistake because it makes it impossible to write common expressions like if (addr & mask == 0) without adding extra parentheses: if ((…

> && and || (which mimics & and |)

I've always thought of it as mimicking * (multiplication) and + (addition), and you can actually use * and + in place of && and || if you wanted to (not advisable, though the idea can be used in expressions to produce branchless code, common technique in GPU shader code). I used to use this trick in TI99/4a BASIC which lacked "AND" and "OR" in "IF" statements, but because boolean expressions evaluated to integer 1 and 0 for true and false, multiplication and addition could serve as AND and OR.

Re: Dennis Ritchie on the priorities of && || vs. == etc. (1982)

#168

Post by ninthcat »

nyssos wrote: post #156
ninthcat wrote: post #122

Earlier quoted context omitted.

You can interpret 0 and 1 as probabilities. 1 + 1 = 1 in this case makes sense because P(A or B) = P(A) + P(B) - P(A and B). You can interpret "A or B" as a set union and "A and B" as a set intersection. Of course it's easy to draw a three-way correspondence between Boolean arithmetic, the events represented by the empty set and the whole space, and sets within some universe because all the objects are so simple, but…

You've just moved the point where we make the arbitrary choice to here: > You can interpret "A or B" as a set union and "A and B" as a set intersection. {True, False, Or, And} and {False, True, And, Or} are two different naming conventions for the exact same structure: the unique boolean algebra on two elements.

A union B is defined as the set of things that are in A or in B; A intersect B is defined as the set of things that are in A and in B. So I don't really see it as an arbitrary choice.

Re: Dennis Ritchie on the priorities of && || vs. == etc. (1982)

#169

Post by teo_zero »

smcameron wrote: post #167
teo_zero wrote: post #135

Please note that, despite the misleading title, TFA is about the precedence of bitwise operators & and | with respect to the comparison operators (== and all the others). In particular it was asked to Ritchie why the former are weaker than the latter in C, a rule generally considered a mistake because it makes it impossible to write common expressions like if (addr & mask == 0) without adding extra parentheses: if ((…

> && and || (which mimics & and |) I've always thought of it as mimicking * (multiplication) and + (addition), and you can actually use * and + in place of && and || if you wanted to (not advisable, though the idea can be used in expressions to produce branchless code, common technique in GPU shader code). I used to use this trick in TI99/4a BASIC which lacked "AND" and "OR" in "IF" statements, but because boolean ex…

But remember that * and + don't short-circuit. This won't work:

  found = (p != NULL) * (*p ! = 0);
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