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bow-swift / bow

🏹 Bow is a cross-platform library for Typed Functional Programming in Swift
https://bow-swift.io
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Typed monad comprehensions #649

Closed ferranpujolcamins closed 3 years ago

ferranpujolcamins commented 3 years ago

Goal

When using monad comprehensions, flatMap is called with values of type Kind<F, Any> and erased functions. From a result point of view, this is fine, as checked by the "Monad comprehensions equivalence to flatMap" law.

However, when debugging, the situation is a little weird because if I set a breakpoint on the implementation of flatMap for a Monad, I cannot know what's the inner type of my Monad at that point, because I always see Kind<F, Any>.

This PR fixes this.

Implementation details

Instead of erasing to Any, BindingExpression now uses Exists. This allows us to call flatMap with the right type, instead of Any.

Testing details

The test is a little bit weird, but I couldn't think of any other way to test this.

ferranpujolcamins commented 3 years ago

I just realised that some unrelated changes slipped into this PR. I removed the unrelated commits and force-pushed.