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module Main where
{-
If a fixity declaration hasn't been supplied for
an operator, it is defaulted to being "infixl 9".
OLD: The derived Read instances for data types containing
left-assoc constructors produces code that causes
non-termination if you use 'read' to evaluate them
( (head (reads x)) is cool tho.)
==> The inferred assoc for :++ below left & the derived
Read instance should fail to terminate (with ghc-4.xx,
this is exemplified by having the stack overflow.)
NEW: the new H98 spec says that we ignore associativity when
parsing, so it terminates fine
-}
-- infixl 9 :++
data T = T1 | T :++ T deriving (Eq,Show, Read)
t :: T
t = read "T1"
main = do
print ((fst (head (reads "T1"))) :: T)
print t
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