Import hs-plugins cvs
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Don Stewart
174
src/altdata/AltData/Dynamic.hs
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174
src/altdata/AltData/Dynamic.hs
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{-# OPTIONS -cpp -fglasgow-exts #-}
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--
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-- Copyright (C) 2004 Don Stewart - http://www.cse.unsw.edu.au/~dons
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--
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-- This library is free software; you can redistribute it and/or
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-- modify it under the terms of the GNU Lesser General Public
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-- License as published by the Free Software Foundation; either
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-- version 2.1 of the License, or (at your option) any later version.
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--
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-- This library is distributed in the hope that it will be useful,
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-- but WITHOUT ANY WARRANTY; without even the implied warranty of
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-- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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-- Lesser General Public License for more details.
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--
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-- You should have received a copy of the GNU Lesser General Public
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-- License along with this library; if not, write to the Free Software
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-- Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
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-- USA
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--
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--
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-- reimplement the Data.Dynamic library to use equality over the
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-- canonical name of a type, rather than on integer keys. The later is
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-- how the Haskell library works, and is broken for our situation:
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-- static versus dynamic instances of the same type seem to generate
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-- different keys, meaning equal types are not detected as such.
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--
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module AltData.Dynamic (
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Dynamic, -- must be abstract
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toDyn, -- :: Typeable a => a -> Dynamic
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fromDyn, -- :: Typeable a => Dynamic -> Maybe a
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fromDynamic,
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dynApp,
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dynApply,
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dynAppHList,
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typecase,
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(-->),
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_Int,
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_Char,
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_Bool,
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_String,
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_IntToInt,
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) where
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import AltData.Typeable
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import Data.Maybe
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import System.IO.Unsafe ( unsafePerformIO )
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import GHC.Base ( unsafeCoerce# )
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import Data.List
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data Dynamic = Dynamic TypeRep Obj
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type Obj = forall a . a
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instance Show Dynamic where
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-- the instance just prints the type representation.
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showsPrec _ (Dynamic t _) =
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showString "<" .
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showsPrec 0 t .
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showString ">"
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instance Typeable Dynamic where
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#if __GLASGOW_HASKELL__ >= 603
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typeOf _ = mkTyConApp (mkTyCon "AltData.Dynamic") []
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#else
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typeOf _ = mkAppTy (mkTyCon "AltData.Dyanmic") []
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#endif
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--
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-- must be monomophic, see Data.Dynamic
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--
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toDyn :: Typeable a => a -> Dynamic
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toDyn v = Dynamic (typeOf v) (unsafeCoerce# v)
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--
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-- Converts a 'Dynamic' object back into an ordinary Haskell value of
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-- the correct type. (this is the same as fromDynamic)
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--
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-- Uses string comparison of the name of the type, rather than the
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-- hashed key of the type, which doesn't work for plugins, which mix
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-- static and dynamic loaded code.
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--
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-- TypeRep is abstract, unfortunately.
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--
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fromDyn :: Typeable a => Dynamic -> Maybe a
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fromDyn (Dynamic t v) =
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case unsafeCoerce# v of
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r | t == typeOf r -> Just r
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| otherwise -> unsafePerformIO (putStrLn $
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"Couldn't match `" ++show(typeOf r) ++
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"' against `" ++show t ++"'"++
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"\n\tExpected type: " ++show(typeOf r) ++
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"\n\tInferred type: " ++show t
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) `seq` Nothing
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fromDynamic d = case fromDyn d of
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Just v -> v
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Nothing -> error ("\nType error in dynamic unwrapping.\n" ++
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"In value `" ++ show d ++ "'")
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dynApp :: Dynamic -> Dynamic -> Dynamic
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dynApp f x = case dynApply f x of
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Just r -> r
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Nothing -> error ("Type error in dynamic application.\n" ++
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"Can't apply function " ++ show f ++
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" to argument " ++ show x)
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--
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-- (f::(a->b)) `dynApply` (x::a) = (f a)::b
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--
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dynApply :: Dynamic -> Dynamic -> Maybe Dynamic
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dynApply (Dynamic t1 f) (Dynamic t2 x) =
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#if __GLASGOW_HASKELL__ >= 603
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case funResultTy t1 t2 of
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#else
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case applyTy t1 t2 of
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#endif
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Just t3 -> Just (Dynamic t3 ((unsafeCoerce# f) x))
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Nothing -> Nothing
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--
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-- hmm
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--
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dynAppHList :: Dynamic -> [Dynamic] -> Dynamic
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dynAppHList fn [] = fn -- partial applicaiton
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dynAppHList fn (x:xs) = (fn `dynApp` x) `dynAppHList` xs
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-- ---------------------------------------------------------------------
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--
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-- Implementation of typecase, without patterns, based on "Dynamic
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-- typing in a statically typed language". Mart\'in Abadi, Luca
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-- Cardelli, Benjamin Pierce and Gordon Plotkin. ACM Trans. Prog. Lang.
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-- and Syst. 13(2):237-268, 1991.
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--
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-- Doesn't provide the behaviour that if the value is not a Dynamic,
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-- then typecase returns a error. Need low-level ops for that.
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--
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-- typecase :: Typeable u => Dynamic -> [(TypeRep, Dynamic)] -> u -> u
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typecase :: Typeable u
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=> Dynamic -- selector
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-> [(Dynamic, Dynamic)] -- branches
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-> u -- else arm
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-> u -- return type
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typecase dv@(Dynamic ty _) alts dflt =
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case find (hasType ty) alts of
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Nothing -> dflt
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Just v -> fromDynamic $ snd v `dynApp` dv
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where hasType t ((Dynamic u _),_) = t == u
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infixl 6 -->
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(-->) :: Typeable b => a -> b -> (a,Dynamic)
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a --> b = (a,toDyn b)
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--
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-- need a way to generate a Dynamic prelude
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--
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_Int = toDyn ( undefined :: Int )
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_Char = toDyn ( undefined :: Char )
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_Bool = toDyn ( undefined :: Bool )
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_String = toDyn ( undefined :: [Char] )
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_IntToInt = toDyn ( undefined :: Int -> Int )
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------------------------------------------------------------------------
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