| 1 | {-# OPTIONS_GHC -fglasgow-exts #-} |
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| 2 | import Control.Monad.ST |
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| 3 | import Data.STRef |
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| 4 | |
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| 5 | data Q s a chain = Node s a chain |
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| 6 | |
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| 7 | data Z a = Z a |
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| 8 | val :: STRef s a -> ST s a |
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| 9 | val = undefined |
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| 10 | |
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| 11 | s :: Q t (Z [Char]) t1 -> [Char] |
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| 12 | s = undefined |
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| 13 | |
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| 14 | r :: a -> STRef s a |
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| 15 | r = undefined |
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| 16 | |
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| 17 | class Zork s a b | a-> b where |
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| 18 | huh:: STRef s (Q s a chain) -> ST s () |
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| 19 | |
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| 20 | foo k = do |
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| 21 | t <- val k |
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| 22 | |
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| 23 | let ref_b = r t |
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| 24 | |
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| 25 | b <- val ref_b |
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| 26 | let abc = s b |
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| 27 | huh ref_b |
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| 28 | -- foo :: (Zork t (Z [Char]) ()) => STRef t (Q t (Z [Char]) t1) -> ST t () when let abc = s b is not commented and foo :: (Zork s a b) => STRef s (Q s a chain) -> ST s () when it is commented. Why? |
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