Why comparing atoms gives typing violation warning? consider: defmodule MyModule do def test do :a < :b end end mix compile my_module.ex gives a warning: Compiling 1 file (.ex) warning: comparison between incompatible types found: :a < :b While Elixir can compare acros…

Because :a and :b are not considered to be of type atom() but respectively as type :a and :b. [image] Elixir v1.17.0-rc.0 released atom() - it represents all atoms and it is divisible. For instance, the atom :foo and :hello_world are also valid (distinct) types.

What’s the result you expected? What are you trying to do?

And as mentioned in the warning the result of the comparison is static as well.

Since the < operator is inlined with :erlang.</2, I expected the compiler to resolve its typing to a parametric polymorphic definition, something akin to (a, a) -> boolean() when a: term(). I didn’t expect singleton types. I gave a simplified example to illustrate the problem, which I encountered w…

[image] bartblast: Since the < operator is inlined with :erlang.</2, I expected the compiler to resolve its typing to a parametric polymorphic definition If the typesystem has distinct types, why would it fall back to less specific types? This would be different if you would have variables he…

@antoine-duchenet @LostKobrakai Guys, considering your previous answers, does this mean that Erlang functions are not treated as “atomic” functions for the type system and they don’t have hardcoded typings? Or maybe the underlying Erlang functions’ abstract code (or bytecode) is analysed as well in …

Not sure I get what you’re asking for, but I don’t think there’s much to it. With 1.17 warnings where implemented to warn when comparisons are made between different types of data – mostly to warn for the common footgun of comparing structs like DateTime, which would use structural comparison not s…

[image] LostKobrakai: Not sure I get what you’re asking for, but I don’t think there’s much to it. He’s probably asking about BIFs and such.

BIFs are a runtime/implementation concern though. The compiler (and the typesystem) generally don’t care about any of that.

So your functions that call them would never be type-checked by Dialyzer whether they pass the right types of arguments to BIFs, is that what you’re saying?

No. I’m saying that a function being implemented as a BIF or not doesn’t matter. Anything happing at compile time happens way before there’s any difference between those.

Typing violation warning when comparing atoms

Questions & Help Questions

antoine-duchenet June 19, 2024, 7:34am 3

Because :a and :b are not considered to be of type atom() but respectively as type :a and :b.