I'm trying to follow some of the code used in the WWDC playgrounds session, I'm trying to import the Cocoa framework with:
Playground execution failed: error: <REPL>:3:8: error: no such module 'Cocoa'
You are using an iOS playground (UIKit-based), not an OS X playground (Cocoa-based). Try creating a new playground and choosing "OS X" as the type instead of "iOS". It should work fine after that.
You can also change the type for an existing playground in the File Inspector (View→Utilities→Show File Inspector) under Playground Settings→Platform.
By default, new iOS playgrounds are created with boilerplate including
import UIKit; OS X playgrounds are created with boilerplate including
import Cocoa, so if you find yourself manually typing "
import Cocoa", it's probably a clue you've got the wrong type.