| ▲ | dwattttt 5 days ago |
| > Either way, you didn't annotate the code so it's kind of pointless to discuss. There are several literals in that code snippet; I could annotate them with their types, and this code would still be exactly as it is. You asked why there are competing type checkers, and the fact that the language is only optionally typed means ambiguity like that example exists, and should be a warning/bug/allowed; choose the type checker that most closely matches the semantics you want to impose. |
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| ▲ | dragonwriter 5 days ago | parent | next [-] |
| > There are several literals in that code snippet; I could annotate them with their types, and this code would still be exactly as it is. Well, no, there is one literal that has an ambiguous type, and if you annotated its type, it would resolve entirely the question of what a typechecker should say; literally the entire reason it is an open question is because that one literal is not annotated. |
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| ▲ | dwattttt 5 days ago | parent [-] | | True, you could annotate 3 of the 4 literals in this without annotating the List, which is ambiguous. In the absence of an explicit annotation (because those are optional), type checkers are left to guess intent to determine whether you wanted a List[Any] or List[number | string], or whether you wanted a List[number] or List[string]. | | |
| ▲ | MangoToupe 5 days ago | parent [-] | | Right. And the fact that python doesn't specify the semantics of its type annotations is a super interesting experiment. Optimally, this will result in a democratic consensus of semantics. Pessimistically, this will result in dialects of semantics that result in dialects of runtime languages as folks adopt type checkers. | | |
| ▲ | dragonwriter 5 days ago | parent [-] | | > And the fact that python doesn't specify the semantics of its type annotations is a super interesting experiment. That hasn't been a fact for quite a while. Npw, it does specify the semantics of its type annotations. It didn't when it first created annotations for Python 3.0 (PEP 3107), but it has progressively since, starting with Python 3.5 (PEP 484) through several subsequent PEPs including creation of the Python Typing Council (PEP 729). | | |
| ▲ | MangoToupe 5 days ago | parent [-] | | So why do the type checkers differ in behavior? | | |
| ▲ | dragonwriter 4 days ago | parent [-] | | The existence of a specification does not make all things striving to implement it compliant with the spec. As the history of web standards (especially back when there were more browsers and the specs weren't entirely controlled by the people making them) illustrates. |
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| ▲ | MangoToupe 5 days ago | parent | prev [-] |
| > I could annotate them with their types, and this code would still be exactly as it is. Well, no, you didn't. Because it's not clear whether the list is a list of value or a list of values of a distinct type. And there are many other ways you could quibble with this statement. |
