Today was a good day. I wrote a somewhat complex piece of logic for a jump planner for EVE online, and, because of the awesomeness of Scala, it worked as conceived, first time.
This is one of the many reasons I love functional programming. As you take your problem and reduce it down to it's most basic components, strip out logic, simplify to a mathematical expression, simplify that expression, suddenly errors become clear in the very writing of it.
Scala feels so much closer to that expression than Java. So much verbosity is inherently prone to error, writing error free code in Scala seems dramatically more possible than in Java.