/usr/lib/hugs/packages/base/Data/Dynamic.hs is in libhugs-base-bundled 98.200609.21-5.4+b3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 | {-# OPTIONS_GHC -fno-implicit-prelude #-}
-----------------------------------------------------------------------------
-- |
-- Module : Data.Dynamic
-- Copyright : (c) The University of Glasgow 2001
-- License : BSD-style (see the file libraries/base/LICENSE)
--
-- Maintainer : libraries@haskell.org
-- Stability : experimental
-- Portability : portable
--
-- The Dynamic interface provides basic support for dynamic types.
--
-- Operations for injecting values of arbitrary type into
-- a dynamically typed value, Dynamic, are provided, together
-- with operations for converting dynamic values into a concrete
-- (monomorphic) type.
--
-----------------------------------------------------------------------------
module Data.Dynamic
(
-- Module Data.Typeable re-exported for convenience
module Data.Typeable,
-- * The @Dynamic@ type
Dynamic, -- abstract, instance of: Show, Typeable
-- * Converting to and from @Dynamic@
toDyn, -- :: Typeable a => a -> Dynamic
fromDyn, -- :: Typeable a => Dynamic -> a -> a
fromDynamic, -- :: Typeable a => Dynamic -> Maybe a
-- * Applying functions of dynamic type
dynApply,
dynApp,
dynTypeRep
) where
import Data.Typeable
import Data.Maybe
import Hugs.Prelude
import Hugs.IO
import Hugs.IORef
import Hugs.IOExts
-------------------------------------------------------------
--
-- The type Dynamic
--
-------------------------------------------------------------
{-|
A value of type 'Dynamic' is an object encapsulated together with its type.
A 'Dynamic' may only represent a monomorphic value; an attempt to
create a value of type 'Dynamic' from a polymorphically-typed
expression will result in an ambiguity error (see 'toDyn').
'Show'ing a value of type 'Dynamic' returns a pretty-printed representation
of the object\'s type; useful for debugging.
-}
dynamicTc = mkTyCon "Dynamic"; instance Typeable Dynamic where { typeOf _ = mkTyConApp dynamicTc [] }
instance Show Dynamic where
-- the instance just prints the type representation.
showsPrec _ (Dynamic t _) =
showString "<<" .
showsPrec 0 t .
showString ">>"
-- | Converts an arbitrary value into an object of type 'Dynamic'.
--
-- The type of the object must be an instance of 'Typeable', which
-- ensures that only monomorphically-typed objects may be converted to
-- 'Dynamic'. To convert a polymorphic object into 'Dynamic', give it
-- a monomorphic type signature. For example:
--
-- > toDyn (id :: Int -> Int)
--
toDyn :: Typeable a => a -> Dynamic
toDyn v = Dynamic (typeOf v) (unsafeCoerce v)
-- | Converts a 'Dynamic' object back into an ordinary Haskell value of
-- the correct type. See also 'fromDynamic'.
fromDyn :: Typeable a
=> Dynamic -- ^ the dynamically-typed object
-> a -- ^ a default value
-> a -- ^ returns: the value of the first argument, if
-- it has the correct type, otherwise the value of
-- the second argument.
fromDyn (Dynamic t v) def
| typeOf def == t = unsafeCoerce v
| otherwise = def
-- | Converts a 'Dynamic' object back into an ordinary Haskell value of
-- the correct type. See also 'fromDyn'.
fromDynamic
:: Typeable a
=> Dynamic -- ^ the dynamically-typed object
-> Maybe a -- ^ returns: @'Just' a@, if the dynamically-typed
-- object has the correct type (and @a@ is its value),
-- or 'Nothing' otherwise.
fromDynamic (Dynamic t v) =
case unsafeCoerce v of
r | t == typeOf r -> Just r
| otherwise -> Nothing
-- (f::(a->b)) `dynApply` (x::a) = (f a)::b
dynApply :: Dynamic -> Dynamic -> Maybe Dynamic
dynApply (Dynamic t1 f) (Dynamic t2 x) =
case funResultTy t1 t2 of
Just t3 -> Just (Dynamic t3 ((unsafeCoerce f) x))
Nothing -> Nothing
dynApp :: Dynamic -> Dynamic -> Dynamic
dynApp f x = case dynApply f x of
Just r -> r
Nothing -> error ("Type error in dynamic application.\n" ++
"Can't apply function " ++ show f ++
" to argument " ++ show x)
dynTypeRep :: Dynamic -> TypeRep
dynTypeRep (Dynamic tr _) = tr
|