Question

Is it possible to have guards on lambda functions?

For example:

\k
    | k < 0     -> "negative"
    | k == 0    -> "zero"
    | otherwise -> "positive"

Answer 1

Other answers show how the extensions LambdaCase and MultiWayIf, introduced since this answer was first written, can solve this. Without them, the nearest direct translation is something a bit like

\k -> case () of
       _ | k < 0     -> "negative"
         | k == 0    -> "zero"
         | otherwise -> "positive"