65 lines
1.9 KiB
Haskell
65 lines
1.9 KiB
Haskell
{-# OPTIONS_GHC -Wall #-}
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module SourceSyntax.Pattern where
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import qualified SourceSyntax.Helpers as Help
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import SourceSyntax.PrettyPrint
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import Text.PrettyPrint as PP
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import qualified Data.Set as Set
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import SourceSyntax.Literal as Literal
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data Pattern = PData String [Pattern]
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| PRecord [String]
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| PAlias String Pattern
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| PVar String
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| PAnything
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| PLiteral Literal.Literal
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deriving (Eq, Ord, Show)
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cons :: Pattern -> Pattern -> Pattern
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cons h t = PData "::" [h,t]
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nil :: Pattern
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nil = PData "[]" []
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list :: [Pattern] -> Pattern
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list = foldr cons nil
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tuple :: [Pattern] -> Pattern
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tuple es = PData ("_Tuple" ++ show (length es)) es
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boundVars :: Pattern -> Set.Set String
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boundVars pattern =
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case pattern of
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PVar x -> Set.singleton x
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PAlias x p -> Set.insert x (boundVars p)
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PData _ ps -> Set.unions (map boundVars ps)
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PRecord fields -> Set.fromList fields
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PAnything -> Set.empty
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PLiteral _ -> Set.empty
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instance Pretty Pattern where
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pretty pattern =
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case pattern of
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PVar x -> variable x
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PLiteral lit -> pretty lit
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PRecord fs -> PP.braces (commaCat $ map variable fs)
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PAlias x p -> prettyParens p <+> PP.text "as" <+> variable x
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PAnything -> PP.text "_"
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PData "::" [hd,tl] -> parensIf isCons (pretty hd) <+> PP.text "::" <+> pretty tl
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where isCons = case hd of
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PData "::" _ -> True
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_ -> False
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PData name ps ->
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if Help.isTuple name then
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PP.parens . commaCat $ map pretty ps
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else hsep (PP.text name : map prettyParens ps)
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prettyParens :: Pattern -> Doc
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prettyParens pattern = parensIf needsThem (pretty pattern)
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where
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needsThem =
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case pattern of
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PData name (_:_) | not (Help.isTuple name) -> True
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PAlias _ _ -> True
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_ -> False
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