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|
-- A nasty deriving test
-- Note the "T2 T1 { f1=3 }" part!
module Main where
infix 4 :%%
data T = Int :%% T
| T1 { f1 :: Int }
| T2 T
deriving( Show, Read )
main = print (read "3 :%% T2 T1 { f1=3 }" :: T)
{- Here's the parser that is produced
import GHC.Read
import Text.ParserCombinators.ReadPrec
import Text.Read
instance Read T where
readPrec =
parens
( prec 4 (
do x <- step readPrec
Symbol ":%%" <- lexP
y <- step readPrec
return (x :%% y))
+++
prec (appPrec+1) (
do Ident "T1" <- lexP
Punc "{" <- lexP
Ident "f1" <- lexP
Punc "=" <- lexP
x <- reset readPrec
Punc "}" <- lexP
return (T1 { f1 = x }))
+++
prec appPrec (
do Ident "T2" <- lexP
x <- step readPrec
return (T2 x))
)
appPrec = 10::Int
-}
|
