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> Prolog came out the same year as C and popularized logic programming, and you can sort of fake assignment with cuts. Can anyone explain to me what this is supposed to mean? (I know Prolog, I understand cuts very well. But I don't know what the author means here.)
I've always had the notion that if I made a language I'd make the operators := and == so it'd be harder to accidentally use the wrong one.
more broadly, why schools are merging reduction and equality in arithmetic ?
What do you mean?
2 + 2 = 4
=
2 + 2 = 2 + 2
2 + 2 = 2 + 1 + 1
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++)"
In pure algorithmic notation, people might use <- or <= instead.
Because K&R had terrible keyboards so they abbreviated everything as much as possible. Traditionally := was used for assignment, which makes sense since it is an asymmetric symbol for an asymmetric operation.
There’s also <-, most commonly seen in R but draws it’s heritage from the APL keyboard
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 "<-".
A classic way to guard against accidental use of assignment in logic statements is to write it "backwards", i.e.:
if (2 == x) {...}