42 lines
1.4 KiB
Haskell
42 lines
1.4 KiB
Haskell
module Pattern (Pattern(..)) where
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import Data.Generics
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data Pattern =
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-- | We don't care what the value is -- will match against any item
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DontCare
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-- | A named "item of interest". Given the specified key, all data items with the same key should be identical (otherwise match errors will be given)
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| Named String Pattern
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-- | A constructed item. This is special because the sub-items may not be of the right type for the constructor,
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-- because they may be special items (such as DontCare)
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| Match Constr [Pattern]
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deriving (Typeable,Show)
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--Tests if patterns are identical, NOT if they'll match the same thing:
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instance Eq Pattern where
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(==) DontCare DontCare = True
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(==) (Named s0 p0) (Named s1 p1) = (s0 == s1) && (p0 == p1)
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(==) (Match c0 ps0) (Match c1 ps1) = (c0 == c1) && (show c0 == show c1) && (ps0 == ps1)
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(==) _ _ = False
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--No proper gunfold, as I still can't figure out to implement it (Constr is problematic)
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instance Data Pattern where
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toConstr (DontCare) = constr_DontCare
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toConstr (Named {}) = constr_Named
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toConstr (Match {}) = constr_Match
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gunfold _ _ _ = error "gunfold Pattern"
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dataTypeOf _ = ty_Pattern
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ty_Pattern = mkDataType "TreeUtil.Pattern"
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[
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constr_DontCare
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,constr_Named
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,constr_Match
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]
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constr_DontCare = mkConstr ty_Pattern "DontCare" [] Prefix
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constr_Named = mkConstr ty_Pattern "Named" [] Prefix
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constr_Match = mkConstr ty_Pattern "Match" [] Prefix
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