Really cute approach to reporting type errors: when there's a type error, show an example of a runtime error that the type check has prevented!
Data-Driven Techniques for Type Error Diagnosis https://escholarship.org/uc/item/59s4h4pv
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Playing with optional type signatures in Python, I realise that the return type is the most important to me.
I'd much rather have a function with only a return type instead of a function with only parameter types. It's often quick to add too.
I've been using "Expected Int, but got String" for my type error messages, but I've been wondering if I could do better.
"Expected Int here, but this value has type String" or "This expression requires Int, but the value is String".
Do you have a favourite?
I'm designing a programming language and trying to decide the type of `let x = 1;`. Should it be Unit or Int?
Advantage of Int: really convenient when evaluating snippets in a REPL.
Advantage of Unit: It's much less confusing when type inference runs on an incomplete function.