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<pre><a name="line-1"></a><span class='hs-comment'>{-# OPTIONS_GHC -XNoImplicitPrelude #-}</span>
<a name="line-2"></a><span class='hs-comment'>-----------------------------------------------------------------------------</span>
<a name="line-3"></a><span class='hs-comment'>-- |</span>
<a name="line-4"></a><span class='hs-comment'>-- Module : Data.Dynamic</span>
<a name="line-5"></a><span class='hs-comment'>-- Copyright : (c) The University of Glasgow 2001</span>
<a name="line-6"></a><span class='hs-comment'>-- License : BSD-style (see the file libraries/base/LICENSE)</span>
<a name="line-7"></a><span class='hs-comment'>-- </span>
<a name="line-8"></a><span class='hs-comment'>-- Maintainer : libraries@haskell.org</span>
<a name="line-9"></a><span class='hs-comment'>-- Stability : experimental</span>
<a name="line-10"></a><span class='hs-comment'>-- Portability : portable</span>
<a name="line-11"></a><span class='hs-comment'>--</span>
<a name="line-12"></a><span class='hs-comment'>-- The Dynamic interface provides basic support for dynamic types.</span>
<a name="line-13"></a><span class='hs-comment'>-- </span>
<a name="line-14"></a><span class='hs-comment'>-- Operations for injecting values of arbitrary type into</span>
<a name="line-15"></a><span class='hs-comment'>-- a dynamically typed value, Dynamic, are provided, together</span>
<a name="line-16"></a><span class='hs-comment'>-- with operations for converting dynamic values into a concrete</span>
<a name="line-17"></a><span class='hs-comment'>-- (monomorphic) type.</span>
<a name="line-18"></a><span class='hs-comment'>-- </span>
<a name="line-19"></a><span class='hs-comment'>-----------------------------------------------------------------------------</span>
<a name="line-20"></a>
<a name="line-21"></a><span class='hs-keyword'>module</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>Dynamic</span>
<a name="line-22"></a> <span class='hs-layout'>(</span>
<a name="line-23"></a>
<a name="line-24"></a> <span class='hs-comment'>-- Module Data.Typeable re-exported for convenience</span>
<a name="line-25"></a> <span class='hs-keyword'>module</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>Typeable</span><span class='hs-layout'>,</span>
<a name="line-26"></a>
<a name="line-27"></a> <span class='hs-comment'>-- * The @Dynamic@ type</span>
<a name="line-28"></a> <span class='hs-conid'>Dynamic</span><span class='hs-layout'>,</span> <span class='hs-comment'>-- abstract, instance of: Show, Typeable</span>
<a name="line-29"></a>
<a name="line-30"></a> <span class='hs-comment'>-- * Converting to and from @Dynamic@</span>
<a name="line-31"></a> <span class='hs-varid'>toDyn</span><span class='hs-layout'>,</span> <span class='hs-comment'>-- :: Typeable a => a -> Dynamic</span>
<a name="line-32"></a> <span class='hs-varid'>fromDyn</span><span class='hs-layout'>,</span> <span class='hs-comment'>-- :: Typeable a => Dynamic -> a -> a</span>
<a name="line-33"></a> <span class='hs-varid'>fromDynamic</span><span class='hs-layout'>,</span> <span class='hs-comment'>-- :: Typeable a => Dynamic -> Maybe a</span>
<a name="line-34"></a>
<a name="line-35"></a> <span class='hs-comment'>-- * Applying functions of dynamic type</span>
<a name="line-36"></a> <span class='hs-varid'>dynApply</span><span class='hs-layout'>,</span>
<a name="line-37"></a> <span class='hs-varid'>dynApp</span><span class='hs-layout'>,</span>
<a name="line-38"></a> <span class='hs-varid'>dynTypeRep</span>
<a name="line-39"></a>
<a name="line-40"></a> <span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-41"></a>
<a name="line-42"></a>
<a name="line-43"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>Typeable</span>
<a name="line-44"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>Maybe</span>
<a name="line-45"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Unsafe</span><span class='hs-varop'>.</span><span class='hs-conid'>Coerce</span>
<a name="line-46"></a>
<a name="line-47"></a><span class='hs-cpp'>#ifdef __GLASGOW_HASKELL__</span>
<a name="line-48"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>GHC</span><span class='hs-varop'>.</span><span class='hs-conid'>Base</span>
<a name="line-49"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>GHC</span><span class='hs-varop'>.</span><span class='hs-conid'>Show</span>
<a name="line-50"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>GHC</span><span class='hs-varop'>.</span><span class='hs-conid'>Exception</span>
<a name="line-51"></a><span class='hs-cpp'>#endif</span>
<a name="line-52"></a>
<a name="line-53"></a><span class='hs-cpp'>#ifdef __HUGS__</span>
<a name="line-54"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Hugs</span><span class='hs-varop'>.</span><span class='hs-conid'>Prelude</span>
<a name="line-55"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Hugs</span><span class='hs-varop'>.</span><span class='hs-conid'>IO</span>
<a name="line-56"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Hugs</span><span class='hs-varop'>.</span><span class='hs-conid'>IORef</span>
<a name="line-57"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Hugs</span><span class='hs-varop'>.</span><span class='hs-conid'>IOExts</span>
<a name="line-58"></a><span class='hs-cpp'>#endif</span>
<a name="line-59"></a>
<a name="line-60"></a><span class='hs-cpp'>#ifdef __NHC__</span>
<a name="line-61"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>NHC</span><span class='hs-varop'>.</span><span class='hs-conid'>IOExtras</span> <span class='hs-layout'>(</span><span class='hs-conid'>IORef</span><span class='hs-layout'>,</span><span class='hs-varid'>newIORef</span><span class='hs-layout'>,</span><span class='hs-varid'>readIORef</span><span class='hs-layout'>,</span><span class='hs-varid'>writeIORef</span><span class='hs-layout'>,</span><span class='hs-varid'>unsafePerformIO</span><span class='hs-layout'>)</span>
<a name="line-62"></a><span class='hs-cpp'>#endif</span>
<a name="line-63"></a>
<a name="line-64"></a><span class='hs-cpp'>#include "Typeable.h"</span>
<a name="line-65"></a>
<a name="line-66"></a><span class='hs-comment'>-------------------------------------------------------------</span>
<a name="line-67"></a><span class='hs-comment'>--</span>
<a name="line-68"></a><span class='hs-comment'>-- The type Dynamic</span>
<a name="line-69"></a><span class='hs-comment'>--</span>
<a name="line-70"></a><span class='hs-comment'>-------------------------------------------------------------</span>
<a name="line-71"></a>
<a name="line-72"></a><span class='hs-comment'>{-|
<a name="line-73"></a> A value of type 'Dynamic' is an object encapsulated together with its type.
<a name="line-74"></a>
<a name="line-75"></a> A 'Dynamic' may only represent a monomorphic value; an attempt to
<a name="line-76"></a> create a value of type 'Dynamic' from a polymorphically-typed
<a name="line-77"></a> expression will result in an ambiguity error (see 'toDyn').
<a name="line-78"></a>
<a name="line-79"></a> 'Show'ing a value of type 'Dynamic' returns a pretty-printed representation
<a name="line-80"></a> of the object\'s type; useful for debugging.
<a name="line-81"></a>-}</span>
<a name="line-82"></a><span class='hs-cpp'>#ifndef __HUGS__</span>
<a name="line-83"></a><a name="Dynamic"></a><span class='hs-keyword'>data</span> <span class='hs-conid'>Dynamic</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Dynamic</span> <span class='hs-conid'>TypeRep</span> <span class='hs-conid'>Obj</span>
<a name="line-84"></a><span class='hs-cpp'>#endif</span>
<a name="line-85"></a>
<a name="line-86"></a><span class='hs-conid'>INSTANCE_TYPEABLE0</span><span class='hs-layout'>(</span><span class='hs-conid'>Dynamic</span><span class='hs-layout'>,</span><span class='hs-varid'>dynamicTc</span><span class='hs-layout'>,</span><span class='hs-str'>"Dynamic"</span><span class='hs-layout'>)</span>
<a name="line-87"></a>
<a name="line-88"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>Show</span> <span class='hs-conid'>Dynamic</span> <span class='hs-keyword'>where</span>
<a name="line-89"></a> <span class='hs-comment'>-- the instance just prints the type representation.</span>
<a name="line-90"></a> <span class='hs-varid'>showsPrec</span> <span class='hs-keyword'>_</span> <span class='hs-layout'>(</span><span class='hs-conid'>Dynamic</span> <span class='hs-varid'>t</span> <span class='hs-keyword'>_</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span>
<a name="line-91"></a> <span class='hs-varid'>showString</span> <span class='hs-str'>"<<"</span> <span class='hs-varop'>.</span>
<a name="line-92"></a> <span class='hs-varid'>showsPrec</span> <span class='hs-num'>0</span> <span class='hs-varid'>t</span> <span class='hs-varop'>.</span>
<a name="line-93"></a> <span class='hs-varid'>showString</span> <span class='hs-str'>">>"</span>
<a name="line-94"></a>
<a name="line-95"></a><span class='hs-cpp'>#ifdef __GLASGOW_HASKELL__</span>
<a name="line-96"></a><span class='hs-comment'>-- here so that it isn't an orphan:</span>
<a name="line-97"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>Exception</span> <span class='hs-conid'>Dynamic</span>
<a name="line-98"></a><span class='hs-cpp'>#endif</span>
<a name="line-99"></a>
<a name="line-100"></a><span class='hs-cpp'>#ifdef __GLASGOW_HASKELL__</span>
<a name="line-101"></a><a name="Obj"></a><span class='hs-keyword'>type</span> <span class='hs-conid'>Obj</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Any</span>
<a name="line-102"></a> <span class='hs-comment'>-- Use GHC's primitive 'Any' type to hold the dynamically typed value.</span>
<a name="line-103"></a> <span class='hs-comment'>--</span>
<a name="line-104"></a> <span class='hs-comment'>-- In GHC's new eval/apply execution model this type must not look</span>
<a name="line-105"></a> <span class='hs-comment'>-- like a data type. If it did, GHC would use the constructor convention </span>
<a name="line-106"></a> <span class='hs-comment'>-- when evaluating it, and this will go wrong if the object is really a </span>
<a name="line-107"></a> <span class='hs-comment'>-- function. Using Any forces GHC to use</span>
<a name="line-108"></a> <span class='hs-comment'>-- a fallback convention for evaluating it that works for all types.</span>
<a name="line-109"></a><span class='hs-cpp'>#elif !defined(__HUGS__)</span>
<a name="line-110"></a><a name="Obj"></a><span class='hs-keyword'>data</span> <span class='hs-conid'>Obj</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Obj</span>
<a name="line-111"></a><span class='hs-cpp'>#endif</span>
<a name="line-112"></a>
<a name="line-113"></a><a name="toDyn"></a><span class='hs-comment'>-- | Converts an arbitrary value into an object of type 'Dynamic'. </span>
<a name="line-114"></a><span class='hs-comment'>--</span>
<a name="line-115"></a><span class='hs-comment'>-- The type of the object must be an instance of 'Typeable', which</span>
<a name="line-116"></a><span class='hs-comment'>-- ensures that only monomorphically-typed objects may be converted to</span>
<a name="line-117"></a><span class='hs-comment'>-- 'Dynamic'. To convert a polymorphic object into 'Dynamic', give it</span>
<a name="line-118"></a><span class='hs-comment'>-- a monomorphic type signature. For example:</span>
<a name="line-119"></a><span class='hs-comment'>--</span>
<a name="line-120"></a><span class='hs-comment'>-- > toDyn (id :: Int -> Int)</span>
<a name="line-121"></a><span class='hs-comment'>--</span>
<a name="line-122"></a><span class='hs-definition'>toDyn</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Typeable</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=></span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Dynamic</span>
<a name="line-123"></a><span class='hs-definition'>toDyn</span> <span class='hs-varid'>v</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Dynamic</span> <span class='hs-layout'>(</span><span class='hs-varid'>typeOf</span> <span class='hs-varid'>v</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-varid'>unsafeCoerce</span> <span class='hs-varid'>v</span><span class='hs-layout'>)</span>
<a name="line-124"></a>
<a name="line-125"></a><a name="fromDyn"></a><span class='hs-comment'>-- | Converts a 'Dynamic' object back into an ordinary Haskell value of</span>
<a name="line-126"></a><span class='hs-comment'>-- the correct type. See also 'fromDynamic'.</span>
<a name="line-127"></a><span class='hs-definition'>fromDyn</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Typeable</span> <span class='hs-varid'>a</span>
<a name="line-128"></a> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>Dynamic</span> <span class='hs-comment'>-- ^ the dynamically-typed object</span>
<a name="line-129"></a> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a</span> <span class='hs-comment'>-- ^ a default value </span>
<a name="line-130"></a> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a</span> <span class='hs-comment'>-- ^ returns: the value of the first argument, if</span>
<a name="line-131"></a> <span class='hs-comment'>-- it has the correct type, otherwise the value of</span>
<a name="line-132"></a> <span class='hs-comment'>-- the second argument.</span>
<a name="line-133"></a><span class='hs-definition'>fromDyn</span> <span class='hs-layout'>(</span><span class='hs-conid'>Dynamic</span> <span class='hs-varid'>t</span> <span class='hs-varid'>v</span><span class='hs-layout'>)</span> <span class='hs-varid'>def</span>
<a name="line-134"></a> <span class='hs-keyglyph'>|</span> <span class='hs-varid'>typeOf</span> <span class='hs-varid'>def</span> <span class='hs-varop'>==</span> <span class='hs-varid'>t</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>unsafeCoerce</span> <span class='hs-varid'>v</span>
<a name="line-135"></a> <span class='hs-keyglyph'>|</span> <span class='hs-varid'>otherwise</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>def</span>
<a name="line-136"></a>
<a name="line-137"></a><a name="fromDynamic"></a><span class='hs-comment'>-- | Converts a 'Dynamic' object back into an ordinary Haskell value of</span>
<a name="line-138"></a><span class='hs-comment'>-- the correct type. See also 'fromDyn'.</span>
<a name="line-139"></a><span class='hs-definition'>fromDynamic</span>
<a name="line-140"></a> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Typeable</span> <span class='hs-varid'>a</span>
<a name="line-141"></a> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>Dynamic</span> <span class='hs-comment'>-- ^ the dynamically-typed object</span>
<a name="line-142"></a> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Maybe</span> <span class='hs-varid'>a</span> <span class='hs-comment'>-- ^ returns: @'Just' a@, if the dynamically-typed</span>
<a name="line-143"></a> <span class='hs-comment'>-- object has the correct type (and @a@ is its value), </span>
<a name="line-144"></a> <span class='hs-comment'>-- or 'Nothing' otherwise.</span>
<a name="line-145"></a><span class='hs-definition'>fromDynamic</span> <span class='hs-layout'>(</span><span class='hs-conid'>Dynamic</span> <span class='hs-varid'>t</span> <span class='hs-varid'>v</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span>
<a name="line-146"></a> <span class='hs-keyword'>case</span> <span class='hs-varid'>unsafeCoerce</span> <span class='hs-varid'>v</span> <span class='hs-keyword'>of</span>
<a name="line-147"></a> <span class='hs-varid'>r</span> <span class='hs-keyglyph'>|</span> <span class='hs-varid'>t</span> <span class='hs-varop'>==</span> <span class='hs-varid'>typeOf</span> <span class='hs-varid'>r</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Just</span> <span class='hs-varid'>r</span>
<a name="line-148"></a> <span class='hs-keyglyph'>|</span> <span class='hs-varid'>otherwise</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Nothing</span>
<a name="line-149"></a>
<a name="line-150"></a><a name="dynApply"></a><span class='hs-comment'>-- (f::(a->b)) `dynApply` (x::a) = (f a)::b</span>
<a name="line-151"></a><span class='hs-definition'>dynApply</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Dynamic</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Dynamic</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Maybe</span> <span class='hs-conid'>Dynamic</span>
<a name="line-152"></a><span class='hs-definition'>dynApply</span> <span class='hs-layout'>(</span><span class='hs-conid'>Dynamic</span> <span class='hs-varid'>t1</span> <span class='hs-varid'>f</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-conid'>Dynamic</span> <span class='hs-varid'>t2</span> <span class='hs-varid'>x</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span>
<a name="line-153"></a> <span class='hs-keyword'>case</span> <span class='hs-varid'>funResultTy</span> <span class='hs-varid'>t1</span> <span class='hs-varid'>t2</span> <span class='hs-keyword'>of</span>
<a name="line-154"></a> <span class='hs-conid'>Just</span> <span class='hs-varid'>t3</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Just</span> <span class='hs-layout'>(</span><span class='hs-conid'>Dynamic</span> <span class='hs-varid'>t3</span> <span class='hs-layout'>(</span><span class='hs-layout'>(</span><span class='hs-varid'>unsafeCoerce</span> <span class='hs-varid'>f</span><span class='hs-layout'>)</span> <span class='hs-varid'>x</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span>
<a name="line-155"></a> <span class='hs-conid'>Nothing</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Nothing</span>
<a name="line-156"></a>
<a name="line-157"></a><a name="dynApp"></a><span class='hs-definition'>dynApp</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Dynamic</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Dynamic</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Dynamic</span>
<a name="line-158"></a><span class='hs-definition'>dynApp</span> <span class='hs-varid'>f</span> <span class='hs-varid'>x</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>case</span> <span class='hs-varid'>dynApply</span> <span class='hs-varid'>f</span> <span class='hs-varid'>x</span> <span class='hs-keyword'>of</span>
<a name="line-159"></a> <span class='hs-conid'>Just</span> <span class='hs-varid'>r</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>r</span>
<a name="line-160"></a> <span class='hs-conid'>Nothing</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>error</span> <span class='hs-layout'>(</span><span class='hs-str'>"Type error in dynamic application.\n"</span> <span class='hs-varop'>++</span>
<a name="line-161"></a> <span class='hs-str'>"Can't apply function "</span> <span class='hs-varop'>++</span> <span class='hs-varid'>show</span> <span class='hs-varid'>f</span> <span class='hs-varop'>++</span>
<a name="line-162"></a> <span class='hs-str'>" to argument "</span> <span class='hs-varop'>++</span> <span class='hs-varid'>show</span> <span class='hs-varid'>x</span><span class='hs-layout'>)</span>
<a name="line-163"></a>
<a name="line-164"></a><a name="dynTypeRep"></a><span class='hs-definition'>dynTypeRep</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Dynamic</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>TypeRep</span>
<a name="line-165"></a><span class='hs-definition'>dynTypeRep</span> <span class='hs-layout'>(</span><span class='hs-conid'>Dynamic</span> <span class='hs-varid'>tr</span> <span class='hs-keyword'>_</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>tr</span>
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