isPos n
    | n<0       = False
    | otherwise = True

isPos n
    | n<0       = False AND print ("negative")
    | otherwise = True  AND print ("positive")

debug = flip trace

isPos n
  | n < 0     = False `debug` "negative"
  | otherwise = True  `debug` "positive"

isPos n
  | n < 0     = False -- `debug` "negative"
  | otherwise = True  -- `debug` "positive"

import Debug.Trace

isPos n
  | n < 0     = trace "negative" False
  | otherwise = trace "positive" True