pat_unreachable.scala:22: warning: patterns after a variable pattern cannot match (SLS 8.1.1)
If you intended to match against parameter b of method contrivedExample, you must use backticks, like: case `b` =>
    case b => println("matched b")
         ^
pat_unreachable.scala:23: warning: unreachable code due to variable pattern 'b' on line 22
If you intended to match against parameter c of method contrivedExample, you must use backticks, like: case `c` =>
    case c => println("matched c")
                     ^
pat_unreachable.scala:24: warning: unreachable code due to variable pattern 'b' on line 22
    case _ => println("matched neither")
                     ^
pat_unreachable.scala:23: warning: unreachable code
    case c => println("matched c")
                     ^
error: No warnings can be incurred under -Xfatal-warnings.
four warnings found
one error found