In his post, Real problems with functional languages [0], Paul Biggar creates a false dichotomy: static types help us to write correct programs while dynamic types let us prototype faster. Dark wants to be able to do both.
I believe Haskell allows us to reject outright incorrect programs sooner and allows us to prototype things faster due to its types and inference engine. I don't really see how Haskell is poor as a prototyping language. From experience it's better than dynamic languages as it has allowed me to focus on logic and domain problems instead of mucking up my code with brittle run-time and equality checks... and then chasing down bugs I've made for myself.
No where is it mentioned what type system Dark is using. Will Dark allow a program to be deployed that it cannot reason about? What about higher-kinded types and polymorphism? Does it enforce termination or is bottom a type in every kind? Does the type system enforce linearity in usage? Quotient types? Row types?
This looks like a cool project but I don't think I'd use it for anything without knowing more about how it works.
[0] https://medium.com/darklang/real-problems-with-functional-la...