never executed always true always false

    1 {-# LANGUAGE CPP #-}
    2 
    3 module GHC.Utils.Constants
    4   ( debugIsOn
    5   , ghciSupported
    6   , isWindowsHost
    7   , isDarwinHost
    8   )
    9 where
   10 
   11 import GHC.Prelude
   12 
   13 {-
   14 
   15 These booleans are global constants, set by CPP flags.  They allow us to
   16 recompile a single module (this one) to change whether or not debug output
   17 appears. They sometimes let us avoid even running CPP elsewhere.
   18 
   19 It's important that the flags are literal constants (True/False). Then,
   20 with -0, tests of the flags in other modules will simplify to the correct
   21 branch of the conditional, thereby dropping debug code altogether when
   22 the flags are off.
   23 -}
   24 
   25 ghciSupported :: Bool
   26 #if defined(HAVE_INTERNAL_INTERPRETER)
   27 ghciSupported = True
   28 #else
   29 ghciSupported = False
   30 #endif
   31 
   32 debugIsOn :: Bool
   33 #if defined(DEBUG)
   34 debugIsOn = True
   35 #else
   36 debugIsOn = False
   37 #endif
   38 
   39 isWindowsHost :: Bool
   40 #if defined(mingw32_HOST_OS)
   41 isWindowsHost = True
   42 #else
   43 isWindowsHost = False
   44 #endif
   45 
   46 isDarwinHost :: Bool
   47 #if defined(darwin_HOST_OS)
   48 isDarwinHost = True
   49 #else
   50 isDarwinHost = False
   51 #endif