A bit over 10 years ago, I remember implementing partial operator precedence in Bison, for an internship. I think it was merged, but I'm not sure anyone ever used it for anything :) The age of Bison for new parsers was already mostly over
Worth noting, WGSL does this too, and is mostly a bit stricter than Zig: `a + b & c` and `a << b & c` are errors in WGSL but accepted by Zig. (Quick: off the top of your head, how do those parse)?
I never realized that languages have so many strict precedence levels because that’s easier to implement than not having them.
This here seems like a very good idea and I hope other languages in active development take note. And als JS’ Prettier, which actively removes parentheses like these.
If you use the shunting yard algorithm or similar for infix binary operators it's trivial to define a table with operator precedence values and use that. You can have a bunch of operators all at the same priority but it is the same complexity really, the algorithm is pretty trivial
I don’t find the article clear on how it fixes things, but I guess that, now
a op1 b op2 c
is an error if op1 is unequal to op2 and they have the same precedence. Do I see that right?
Also, it seems each operator will have to have a associativity to handle a future operator for exponentiation or (also potential future) custom operators.
Finally, the “What you need to know” section doesn’t mention orelse. Where does that fit in?
The point is that there is no longer a global ‘precedence number’ where the operator with the higher precedence binds tighter. Instead, it is only valid to write your example for some combinations of op1 and op2; other combinations will require explicit parentheses.
Presumably orelse is not in the table because it requires parentheses for any other operator.
Here is a crazy idea, don’t use operators, just use functions.
Operators cause issues because it is not possible to cleanly express error output from an operator, it is not possible to express the bit-width of the operation, have to understand precedence.
All of these issues cause other downstream issues.
Because it's ridiculously verbose. Abbreviating extremely common operations makes code far easier to read and understand than not.
> have to understand precedence
Precedence is not in any way an argument against using operators; you could disallow precedence at all (eg. each expression must have at most one operator, or rather two counting the assignment operator) while still having operators. That said, precedence is also very beneficial to readability when not abused.
> Operators cause issues because it is not possible to cleanly express error output from an operator
Incorrect. An operator can simply desugar to functions, and therefore has the exact same error semantic possibilities. If you take issue with a language not returning errors from operators, that is a language design issue, not something inherent to the existence of operators.
I don't think your experience is particularly universal, it vastly differs depending on what kind of programming you do. If you're doing games stuff or graphics or signal processing or any other number of subfields of programming that require a lot of math, operators are a god-send for readability.
This Zig change is the best of both worlds: avoid the ambiguity, but keep the readability.
There are plenty of languages, like e.g. Ruby, where operators are just sugar for functions or methods. Meaning they can still be partially applied, have their value taken, and/or passed as callbacks.
If your language doesn't allow you to do the same thing with operators as you can do with functions, that's a language design issue and has nothing to do with operators as a concept.
> The amount of times I've been sad that multiply or sum are longer than + or * is limited to long formulas and even then it's a non issue.
It depends on what things you work on. When I'm writing 'math-y' code (GPU shaders for renderng etc) then I want the expressions to look close to the reference paper and not artificially split them up into multiple lines of code with function calls instead of operators.
I don't think character length of an expression is the issue. Reading chained operators is explicitly easier than reading nested functions by virtue of operators having infix notation and not explicitly requiring parantheses where they are not necessary to disambiguate order of operations. The prefix notation of functions moves the operation farther from the eye from operands and introduces the issue of parantheses-miscounting bugs. I'd hardly say the difference in readability of these is a non issue:
Operators can also support those things. Operators are just syntax sugar for functions, or at least they're capable of being such. If a language chooses not to support the full range of what functions can do for operators, that is a thing you can criticise the language for (and I do!), but it is not a reason to suggest operators should be disposed with in language design altogether.
Personally I think the meaning of + and * should be context dependent.
Though the main reason for infix notation is to signal associativity. Which a lot of these don't satisfy.
A lot of these are just trying to mimic natural language, which can be useful but as lisp demonstrates is not that important if the grammar is clear enough.
Zig sometimes gives you this, for example there are @divCeil, @divTrunc, @divExact, and @divFloor built-ins so that you can be more precise in your intent compared to using "/". It's rather simple to then write a linting rule that fails if you ever have a literal "/" in your codebase.
This is one of those ideas that is very weird if you’re approaching it from more or less traditional parsing techniques, but makes a lot of sense when you think about it.
I ended up doing a bunch of work on it in a slightly broader and more formal setting during my phd (https://dl.acm.org/doi/abs/10.1145/3571251) with the expectation that it probably wouldn’t be relevant for more mainstream languages any time soon, very happy to be wrong on that.
C/C++ obviously have far too many precedence levels, but you can easily have a more readable tower without forcing parentheses, like Go's 5 levels: https://go.dev/ref/spec#Operator_precedence
JavaScript does something similar for the exponentiation operator. This is a syntax error:
-a ** b
Someone who learned PEMDAS in school may argue it should be equivalent to -(a * b), while a programmer may be used to unary operators binding tightest, so (-a) * b.
This is very clearly the best design for operator precedence IMO and it's nice that Zig has converged on it. It would be good to get it as a linting/formatting rule in Rust too (maybe that already exists?).
Funny that they named it "orelse" which sounds like a conditional threat to me :)
Yes, felt this way when I was learning Ada. Semantics differ.
Also, no zig `andthen` :)
A bit over 10 years ago, I remember implementing partial operator precedence in Bison, for an internship. I think it was merged, but I'm not sure anyone ever used it for anything :) The age of Bison for new parsers was already mostly over
Worth noting, WGSL does this too, and is mostly a bit stricter than Zig: `a + b & c` and `a << b & c` are errors in WGSL but accepted by Zig. (Quick: off the top of your head, how do those parse)?
I'm thinking of doing this for symbolasm also.
Something very similar was in Fortress, see 16.2 here https://www.ccs.neu.edu/home/samth/fortress-spec.pdf
I never realized that languages have so many strict precedence levels because that’s easier to implement than not having them.
This here seems like a very good idea and I hope other languages in active development take note. And als JS’ Prettier, which actively removes parentheses like these.
Things become error prone once you realize that the precedence rules are different across languages!
No you can have no precedence at all see Lisp and APL for examples.
Lisp because everything is explicit and only the form just inside an opening parenthesis does anything. APL as all is scanned right to left.
If you use the shunting yard algorithm or similar for infix binary operators it's trivial to define a table with operator precedence values and use that. You can have a bunch of operators all at the same priority but it is the same complexity really, the algorithm is pretty trivial
I don’t find the article clear on how it fixes things, but I guess that, now
is an error if op1 is unequal to op2 and they have the same precedence. Do I see that right?Also, it seems each operator will have to have a associativity to handle a future operator for exponentiation or (also potential future) custom operators.
Finally, the “What you need to know” section doesn’t mention orelse. Where does that fit in?
The point is that there is no longer a global ‘precedence number’ where the operator with the higher precedence binds tighter. Instead, it is only valid to write your example for some combinations of op1 and op2; other combinations will require explicit parentheses.
Presumably orelse is not in the table because it requires parentheses for any other operator.
I would hope they implemented it with precedence numbers, as any other way is likely to be harder to write and lead to inconsistencies.
It’s harder to write because users will want to use expressions with more than one operator such as
Here is a crazy idea, don’t use operators, just use functions.
Operators cause issues because it is not possible to cleanly express error output from an operator, it is not possible to express the bit-width of the operation, have to understand precedence.
All of these issues cause other downstream issues.
Why not add_u64()?
Because it's ridiculously verbose. Abbreviating extremely common operations makes code far easier to read and understand than not.
> have to understand precedence
Precedence is not in any way an argument against using operators; you could disallow precedence at all (eg. each expression must have at most one operator, or rather two counting the assignment operator) while still having operators. That said, precedence is also very beneficial to readability when not abused.
> Operators cause issues because it is not possible to cleanly express error output from an operator
Incorrect. An operator can simply desugar to functions, and therefore has the exact same error semantic possibilities. If you take issue with a language not returning errors from operators, that is a language design issue, not something inherent to the existence of operators.
The amount of times I've been sad that multiply or sum are longer than + or * is limited to long formulas and even then it's a non issue.
Also, functions can be used as callbacks, and offer overloads to handle partial applications with ease, pipe(2, sum(3), multiply(2)), e.g.
I don't think your experience is particularly universal, it vastly differs depending on what kind of programming you do. If you're doing games stuff or graphics or signal processing or any other number of subfields of programming that require a lot of math, operators are a god-send for readability.
This Zig change is the best of both worlds: avoid the ambiguity, but keep the readability.
There are plenty of languages, like e.g. Ruby, where operators are just sugar for functions or methods. Meaning they can still be partially applied, have their value taken, and/or passed as callbacks.
If your language doesn't allow you to do the same thing with operators as you can do with functions, that's a language design issue and has nothing to do with operators as a concept.
> The amount of times I've been sad that multiply or sum are longer than + or * is limited to long formulas and even then it's a non issue.
It depends on what things you work on. When I'm writing 'math-y' code (GPU shaders for renderng etc) then I want the expressions to look close to the reference paper and not artificially split them up into multiple lines of code with function calls instead of operators.
I don't think character length of an expression is the issue. Reading chained operators is explicitly easier than reading nested functions by virtue of operators having infix notation and not explicitly requiring parantheses where they are not necessary to disambiguate order of operations. The prefix notation of functions moves the operation farther from the eye from operands and introduces the issue of parantheses-miscounting bugs. I'd hardly say the difference in readability of these is a non issue:
(a + b + c + d) * e
mult(add(a, add(b, add(c, d))), e)
> (a + b + c + d) * e
> mult(add(a, add(b, add(c, d))), e)mult(add(a, b, c, d), e)
:)
At that point,
Hence I said that operators are more readable for longer formulas.
Operators can also support those things. Operators are just syntax sugar for functions, or at least they're capable of being such. If a language chooses not to support the full range of what functions can do for operators, that is a thing you can criticise the language for (and I do!), but it is not a reason to suggest operators should be disposed with in language design altogether.
For even cleaner expression, let’s just draw the whole program as a syntax tree.
Personally I think the meaning of + and * should be context dependent.
Though the main reason for infix notation is to signal associativity. Which a lot of these don't satisfy.
A lot of these are just trying to mimic natural language, which can be useful but as lisp demonstrates is not that important if the grammar is clear enough.
People disagree about that characterization of Lisp.
Zig sometimes gives you this, for example there are @divCeil, @divTrunc, @divExact, and @divFloor built-ins so that you can be more precise in your intent compared to using "/". It's rather simple to then write a linting rule that fails if you ever have a literal "/" in your codebase.
...and while at why not also dump the assignment and indexing operators!
(I bet I messed up the parentheses somewhere).At that point, even assembly code is more readable. Also there's a reason why Lisp and Forth haven't exactly taken the world by storm ;)
This is one of those ideas that is very weird if you’re approaching it from more or less traditional parsing techniques, but makes a lot of sense when you think about it.
I ended up doing a bunch of work on it in a slightly broader and more formal setting during my phd (https://dl.acm.org/doi/abs/10.1145/3571251) with the expectation that it probably wouldn’t be relevant for more mainstream languages any time soon, very happy to be wrong on that.
Saturating vs wrapping operators are so nice! Apparently compiles to 3 or 4 branchless ops on most architectures.
C/C++ obviously have far too many precedence levels, but you can easily have a more readable tower without forcing parentheses, like Go's 5 levels: https://go.dev/ref/spec#Operator_precedence
`a + b | c + d` is still confusing and prone to misinterpretation in that scheme.
JavaScript does something similar for the exponentiation operator. This is a syntax error:
Someone who learned PEMDAS in school may argue it should be equivalent to -(a * b), while a programmer may be used to unary operators binding tightest, so (-a) * b.I like the compromise, although I still think operator precedence in itself is evil :P Lisp kinda made the right call by mistake.
Made the right call, yes, but at the right time and with the right parameters above all!
So did Forth, but that's no guarantee for readability. APL got the worst of both worlds, IMO.
This is very clearly the best design for operator precedence IMO and it's nice that Zig has converged on it. It would be good to get it as a linting/formatting rule in Rust too (maybe that already exists?).