shithub: MicroHs

Info  •  Files  •  Log  •  Branches

More Read

--- a/lib/Text/Read.hs

+++ b/lib/Text/Read.hs

@@ -82,3 +82,14 @@

   readsPrec p = readParen (p > 10) $ \ r ->

                 [ (Left  a, t) | ("Left",  s) <- lex r, (a, t) <- readsPrec 11 s ] ++

                 [ (Right b, t) | ("Right", s) <- lex r, (b, t) <- readsPrec 11 s ]

+

+instance Read () where  

+  readsPrec p  = readParen False $

+                   \ r -> [((),t) | ("(",s) <- lex r,

+                                    (")",t) <- lex s ]

+

+instance forall a b . (Read a, Read b) => Read (a,b)  where

+  readsPrec p = readParen True $

+                  \ r -> [((a, b), u) | (a, s)   <- reads r,

+                                        (",", t) <- lex s,

+                                        (b, u)   <- reads t ]

--- a/tests/Read.hs

+++ b/tests/Read.hs

@@ -45,3 +45,5 @@

   print (readMaybe "Just Just 123" :: Maybe (Maybe (Maybe Int)))

   print (read "Left True" :: Either Bool Int)

   print (read "Right 123" :: Either Bool Int)

+  print (read "()" :: ())

+  print (read "(True,123)" :: (Bool, Int))

--- a/tests/Read.ref

+++ b/tests/Read.ref

@@ -35,3 +35,5 @@

 Nothing

 Left True

 Right 123

+()

+(True,123)

-- 

⑨