1 files changed, 51 insertions, 0 deletions
diff --git a/compiler/GHC/Utils/Constants.hs b/compiler/GHC/Utils/Constants.hs
new file mode 100644
index 0000000000..518c5f31be
--- /dev/null
+++ b/compiler/GHC/Utils/Constants.hs
@@ -0,0 +1,51 @@
+{-# LANGUAGE CPP #-}
+
+module GHC.Utils.Constants
+  ( debugIsOn
+  , ghciSupported
+  , isWindowsHost
+  , isDarwinHost
+  )
+where
+
+import GHC.Prelude
+
+{-
+
+These booleans are global constants, set by CPP flags.  They allow us to
+recompile a single module (this one) to change whether or not debug output
+appears. They sometimes let us avoid even running CPP elsewhere.
+
+It's important that the flags are literal constants (True/False). Then,
+with -0, tests of the flags in other modules will simplify to the correct
+branch of the conditional, thereby dropping debug code altogether when
+the flags are off.
+-}
+
+ghciSupported :: Bool
+#if defined(HAVE_INTERNAL_INTERPRETER)
+ghciSupported = True
+#else
+ghciSupported = False
+#endif
+
+debugIsOn :: Bool
+#if defined(DEBUG)
+debugIsOn = True
+#else
+debugIsOn = False
+#endif
+
+isWindowsHost :: Bool
+#if defined(mingw32_HOST_OS)
+isWindowsHost = True
+#else
+isWindowsHost = False
+#endif
+
+isDarwinHost :: Bool
+#if defined(darwin_HOST_OS)
+isDarwinHost = True
+#else
+isDarwinHost = False
+#endif