Thanks for the tip! Haskell IDE engine is exactly what I've been using til now and would've been very pleased to find out it had such a convenient feature.
Ghcide is on my list to try next as it's gotten a lot of attention lately.
Yes, it already has a code command to automatically add top level type annotations. The caveat I that it can only work if you add -Wall to your compilations flags.
Ghcide is on my list to try next as it's gotten a lot of attention lately.