Add Pretty instances for Lists and pairs.

[dead/harbl.git] / src / Pretty.hs

diff --git a/src/Pretty.hs b/src/Pretty.hs
index 360bd4c1b8a4ded3875972f8a30c195284051c5e..91158065ff717ddc71bc2b909c25ee422de49e7d 100644 (file)
--- a/src/Pretty.hs
+++ b/src/Pretty.hs
@@ -7,7 +7,7 @@
 --   way. The 'pretty_print' function then prints the result of
 --   'pretty_show' by default.
 --
-module Pretty
+module Pretty ( Pretty(..) )
 where
 
 import Text.Parsec ( ParseError )
@@ -22,6 +22,21 @@ class Pretty a where
   pretty_print = putStrLn . pretty_show
 
 
+-- | If we can pretty print something, we can pretty-print a list of
+--   them too.
+--
+instance (Pretty a) => Pretty [a] where
+  pretty_show l = show $ map pretty_show l
+
+
+-- | If we can pretty print something, we can pretty-print a pair of
+--   them too.
+--
+instance (Pretty a, Pretty b) => Pretty (a,b) where
+  pretty_show (x,y) = show $ (pretty_show x, pretty_show y)
+
+
+
 -- | Define a 'Pretty' instance for the result of 'parse'. This lets
 --   us pretty-print the result of a parse attempt without worrying
 --   about whether or not it failed. If the parse failed, you get the