<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> <html> <head> <!-- Generated by HsColour, http://www.cs.york.ac.uk/fp/darcs/hscolour/ --> <title>src/ForSyDe/OSharing/UDynamic.hs</title> <link type='text/css' rel='stylesheet' href='hscolour.css' /> </head> <body> <pre><a name="line-1"></a><span class='hs-comment'>-----------------------------------------------------------------------------</span> <a name="line-2"></a><span class='hs-comment'>-- |</span> <a name="line-3"></a><span class='hs-comment'>-- Module : ForSyDe.OSharing</span> <a name="line-4"></a><span class='hs-comment'>-- Copyright : (c) SAM Group, KTH/ICT/ECS 2007-2008</span> <a name="line-5"></a><span class='hs-comment'>-- License : BSD-style (see the file LICENSE)</span> <a name="line-6"></a><span class='hs-comment'>-- </span> <a name="line-7"></a><span class='hs-comment'>-- Maintainer : forsyde-dev@ict.kth.se</span> <a name="line-8"></a><span class='hs-comment'>-- Stability : experimental</span> <a name="line-9"></a><span class='hs-comment'>-- Portability : non-portable (GHC libraries)</span> <a name="line-10"></a><span class='hs-comment'>--</span> <a name="line-11"></a><span class='hs-comment'>-- This module provides support for unsafe dynamic typing.</span> <a name="line-12"></a><span class='hs-comment'>--</span> <a name="line-13"></a><span class='hs-comment'>-- Use with care. Normally, "Data.Dynamic" is preferred since it provides a</span> <a name="line-14"></a><span class='hs-comment'>-- safe casting operation thanks to the use of "Data.Typeable". </span> <a name="line-15"></a><span class='hs-comment'>--</span> <a name="line-16"></a><span class='hs-comment'>-- /This module is based on Lava2000/: <<a href="http://www.cs.chalmers.se/~koen/Lava/">http://www.cs.chalmers.se/~koen/Lava/</a>></span> <a name="line-17"></a><span class='hs-comment'>-- </span> <a name="line-18"></a><span class='hs-comment'>-----------------------------------------------------------------------------</span> <a name="line-19"></a><span class='hs-keyword'>module</span> <span class='hs-conid'>ForSyDe</span><span class='hs-varop'>.</span><span class='hs-conid'>OSharing</span><span class='hs-varop'>.</span><span class='hs-conid'>UDynamic</span> <a name="line-20"></a> <span class='hs-layout'>(</span><span class='hs-conid'>UDynamic</span><span class='hs-layout'>,</span> <a name="line-21"></a> <span class='hs-varid'>unsafeToUDyn</span><span class='hs-layout'>,</span> <a name="line-22"></a> <span class='hs-varid'>unsafeFromUDyn</span><span class='hs-layout'>)</span> <a name="line-23"></a> <a name="line-24"></a> <span class='hs-keyword'>where</span> <a name="line-25"></a> <a name="line-26"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Unsafe</span><span class='hs-varop'>.</span><span class='hs-conid'>Coerce</span> <span class='hs-layout'>(</span><span class='hs-varid'>unsafeCoerce</span><span class='hs-layout'>)</span> <a name="line-27"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>GHC</span><span class='hs-varop'>.</span><span class='hs-conid'>Base</span> <span class='hs-layout'>(</span><span class='hs-conid'>Any</span><span class='hs-layout'>)</span> <a name="line-28"></a> <a name="line-29"></a><a name="UDynamic"></a><span class='hs-comment'>-- | A value of type 'UDynamic' (from Unsafe Dynamic) can</span> <a name="line-30"></a><a name="UDynamic"></a><span class='hs-comment'>-- implicitly any Haskell value. </span> <a name="line-31"></a><a name="UDynamic"></a><span class='hs-comment'>--</span> <a name="line-32"></a><a name="UDynamic"></a><span class='hs-comment'>-- It is unsafe because, as opposed to 'Data.Dynamic', </span> <a name="line-33"></a><a name="UDynamic"></a><span class='hs-comment'>--- it does not encapsule type information and does</span> <a name="line-34"></a><a name="UDynamic"></a><span class='hs-comment'>-- it makes unsafe to cast a 'UDynamic' back to its original Haskell type.</span> <a name="line-35"></a><a name="UDynamic"></a><span class='hs-keyword'>data</span> <span class='hs-conid'>UDynamic</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>UDynamic</span> <span class='hs-conid'>Any</span> <a name="line-36"></a> <a name="line-37"></a><a name="unsafeToUDyn"></a><span class='hs-comment'>-- | Converts an arbitrary value into an object of type 'UDynamic'.</span> <a name="line-38"></a><span class='hs-comment'>-- It is unsafe because it does not provide type information during the </span> <a name="line-39"></a><span class='hs-comment'>-- transformation</span> <a name="line-40"></a><span class='hs-definition'>unsafeToUDyn</span> <span class='hs-keyglyph'>::</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>UDynamic</span> <a name="line-41"></a><span class='hs-definition'>unsafeToUDyn</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>UDynamic</span> <span class='hs-layout'>(</span><span class='hs-varid'>unsafeCoerce</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <a name="line-42"></a> <a name="line-43"></a><a name="unsafeFromUDyn"></a><span class='hs-comment'>-- | Converts a 'UDynamic' object back into an ordinary Haskell value.</span> <a name="line-44"></a><span class='hs-comment'>-- It is unsafe because there is no way to unsure converting</span> <a name="line-45"></a><span class='hs-comment'>-- back to the correct original Haskell type. Thus, this</span> <a name="line-46"></a><span class='hs-comment'>-- function should be used with care since it can cuase disastrous errors.</span> <a name="line-47"></a><span class='hs-comment'>-- </span> <a name="line-48"></a><span class='hs-comment'>-- e.g. disastrousCast :: a -> b</span> <a name="line-49"></a><span class='hs-comment'>-- disastrousCast = unsafeToDyn . unsafeFromDyn</span> <a name="line-50"></a><span class='hs-comment'>--</span> <a name="line-51"></a><span class='hs-comment'>-- The following program would coredump</span> <a name="line-52"></a><span class='hs-comment'>-- main = putStr (disastrousCast 1 :: String) </span> <a name="line-53"></a><span class='hs-definition'>unsafeFromUDyn</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>UDynamic</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a</span> <a name="line-54"></a><span class='hs-definition'>unsafeFromUDyn</span> <span class='hs-layout'>(</span><span class='hs-conid'>UDynamic</span> <span class='hs-varid'>obj</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>unsafeCoerce</span> <span class='hs-varid'>obj</span> </pre></body> </html>
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