51 lines
1.4 KiB
Haskell
51 lines
1.4 KiB
Haskell
-- | A generic show implementation that pretty-prints expressions.
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-- This ought to use a class (like show does), so that it can be extended
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-- properly without me needing to have FCO-specific cases in here -- see the
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-- appropriate SYB paper.
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module PrettyShow (pshow) where
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import Data.Generics
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import Text.PrettyPrint.HughesPJ
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import Metadata
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-- This is ugly -- but it looks like you can't easily define a generic function
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-- even for a single tuple type, since it has to parameterise over multiple Data
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-- types...
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isTupleCtr :: String -> Bool
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isTupleCtr ('(':cs) = checkRest cs
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where
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checkRest ",)" = True
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checkRest (',':cs) = checkRest cs
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checkRest _ = False
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isTupleCtr _ = False
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doGeneral :: Data a => a -> Doc
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doGeneral t =
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if isTupleCtr cn then
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parens $ sep $ punctuate (text ",") l
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else case l of
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[] -> con
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otherwise -> parens $ sep (con : l)
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where
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cn = showConstr (toConstr t)
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con = text $ cn
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l = gmapQ doAny t
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doList :: Data a => [a] -> Doc
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doList t = brackets $ sep $ punctuate (text ",") (map doAny t)
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doString :: String -> Doc
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doString s = text $ show s
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doMeta :: Meta -> Doc
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doMeta m = text $ show m
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doAny :: Data a => a -> Doc
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doAny = doGeneral `ext1Q` doList `extQ` doString `extQ` doMeta
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-- | Convert an arbitrary data structure to a string in a reasonably pretty way.
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-- This is currently rather slow.
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pshow :: Data a => a -> String
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pshow x = render $ doAny x
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