Haskell foldl signature is in unexpected notation

I have checked signature of foldl function and this is the result:

> :t foldl  foldl :: Foldable t => (b -> a -> b) -> b -> t a -> b  

I am confused about this part t a ->b what does this part mean?
Is my guess correct that it means that 3rd argument of foldl function is a Foldable data structure which contains elements of type a?

https://stackoverflow.com/questions/65605304/haskell-foldl-signature-is-in-unexpected-notation January 07, 2021 at 09:00AM