Is there already any collection of best practices for languages like Scala?
I\'ve found a work on design patterns for functional languages, Design patterns for funct
Closely related, you might want to explore data structures as defined in purely functional (or hybrid functional) languages. For one, the ability to treat functions as first-class values make some patterns (like visitor, template method or decorator) unnecessary in some (not all) contexts. Secondly, data structures (and the algorithms that operate on them) are either the plumbing for design patterns, or present certain problems that design patterns attempt to address, see Wikipedia article Purely functional.
Better yet, I'd refer you to Okasaki's thesis on purely functional data structures.