[blauditore]

I think the underlying problem is that in cases of long inference chains, it's hard to detect where the problem lies if types on both ends don't match. In my experience, the compiler will just show an error on the "latter" end, then the user needs to trace inference back and figure out where things went wrong.

Personally, I experience this quite often, e.g. in Java whenever arrow functions are heavily used, such as with streams.

It would be nice to have compilers report the whole inference chain somehow, just to be clear about all possible spots where things might be wrong. But I suppose that's difficult to visualize in a well human-readable way.

[pkolaczk]

Some IDEs show type hints on hover, or if type mismatch is detected, they display inferred types inline in code. E.g Intellij Idea does that for Scala and it is really useful. I wish it did that in Java as well.

[papln]

> But I suppose that's difficult to visualize in a well human-readable way.

It's not. The type-checker must have constructed a call stack of inferred types in order to find the violation, so it simply has to print all the calls (source line and line number) and the types it deduced, and let the programmer (or IDE) compare that to the code in context and look for surprises.