logging module

affection.cabal

@@ -30,12 +30,34 @@ source-repository head
   type:     git
   location: https://github.com/nek0/affection
 
+flag debug
+  description:       Enable debug messages
+  default:           False
+  manual:            True
+
+flag warn
+  description:       Enable warning messages
+  default:           False
+  manual:            True
+
+flag error
+  description:       Enable error messages
+  default:           False
+  manual:            True
+
 flag examples
   description:       Build example programs
   default:           False
 
 library
+  if flag(debug)
+    cpp-options:       -DDEBUG
+  if flag(warn)
+    cpp-options:       -DWARN
+  if flag(error)
+    cpp-options:       -DERROR
   exposed-modules:     Affection
+                     , Affection.Logging
                      , Affection.Types
                      , Affection.StateMachine
                      , Affection.MouseInteractable

src/Affection/Logging.hs

@@ -0,0 +1,33 @@
+{-# LANGUAGE CPP #-}
+module Affection.Logging where
+
+import Debug.Trace
+
+data LogLevel
+  = Debug
+  | Warn
+  | Error
+
+log :: LogLevel -> String -> a -> a
+#if defined(DEBUG)
+log Debug s = trace ("DEBUG: " ++ s)
+#endif
+#if defined(WARN) || defined(DEBUG)
+log Warn s = trace ("WARN: " ++ s)
+#endif
+#if defined(ERROR) || defined(WARN) || defined(DEBUG)
+log Error s = trace ("ERROR: " ++ s)
+#endif
+log _ _ = id
+
+logIO :: LogLevel -> String -> IO ()
+#if defined(DEBUG)
+logIO Debug s = traceIO ("DEBUG: " ++ s)
+#endif
+#if defined(WARN) || defined(DEBUG)
+logIO Warn s = traceIO ("WARN: " ++ s)
+#endif
+#if defined(ERROR) || defined(WARN) || defined(DEBUG)
+logIO Error s = traceIO ("ERROR: " ++ s)
+#endif
+logIO _ _ = return ()