108 lines
5.6 KiB
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108 lines
5.6 KiB
HTML
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<head><title>30 Foreign.Marshal</title>
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<!--l. 1--><div class="crosslinks"><p class="noindent">[<a
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href="haskellch31.html" >next</a>] [<a
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<h2 class="chapterHead"><span class="titlemark">Chapter 30</span><br /><a
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id="x38-28500030"></a><span
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class="pcrr7t-">Foreign.Marshal</span></h2>
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<div class="quote">
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<div class="verbatim" id="verbatim-444">
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module Foreign.Marshal (
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 <br />    module Foreign.Marshal.Alloc,  module Foreign.Marshal.Array,
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 <br />    module Foreign.Marshal.Error,  module Foreign.Marshal.Utils,
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 <br />    unsafeLocalState
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 <br />  ) where
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</div>
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<p class="noindent"></div>
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<p class="noindent"> The module <span
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class="pcrr7t-">Foreign.Marshal </span>re-exports the other modules in the <span
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class="pcrr7t-">Foreign.Marshal </span>hierarchy:
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<dl> <dt class="haddockdesc">
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<!--tex4ht:inline--><div class="tabular"> <table id="TBL-522" class="tabular"
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cellspacing="0" cellpadding="0" rules="groups"
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><colgroup id="TBL-522-1g"><col
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id="TBL-522-1" /></colgroup><tr
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style="vertical-align:baseline;" id="TBL-522-1-"><td style="white-space:nowrap; text-align:left;" id="TBL-522-1-1"
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class="td11"><span
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class="pcrb7t-">module</span><span
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class="pcrb7t-"> Foreign.Marshal.Alloc </span></td>
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</tr><tr
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style="vertical-align:baseline;" id="TBL-522-2-"><td style="white-space:nowrap; text-align:left;" id="TBL-522-2-1"
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class="td11"><span
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class="pcrb7t-">module</span><span
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class="pcrb7t-"> Foreign.Marshal.Array </span></td>
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</tr><tr
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style="vertical-align:baseline;" id="TBL-522-3-"><td style="white-space:nowrap; text-align:left;" id="TBL-522-3-1"
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class="td11"><span
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class="pcrb7t-">module</span><span
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class="pcrb7t-"> Foreign.Marshal.Error </span></td>
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</tr><tr
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style="vertical-align:baseline;" id="TBL-522-4-"><td style="white-space:nowrap; text-align:left;" id="TBL-522-4-1"
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class="td11"><span
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class="pcrb7t-">module</span><span
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class="pcrb7t-"> Foreign.Marshal.Utils </span></td>
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</tr></table> </div> <dd class="haddockdesc">
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</dl>
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<p class="noindent"> and provides one function:
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<dl> <dt class="haddockdesc">
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<!--tex4ht:inline--><div class="tabular"> <table id="TBL-523" class="tabular"
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cellspacing="0" cellpadding="0" rules="groups"
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><colgroup id="TBL-523-1g"><col
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id="TBL-523-1" /></colgroup><tr
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style="vertical-align:baseline;" id="TBL-523-1-"><td style="white-space:nowrap; text-align:left;" id="TBL-523-1-1"
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class="td11"><span
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class="pcrb7t-">unsafeLocalState</span><span
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class="pcrb7t-"> ::</span><span
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class="pcrb7t-"> IO</span><span
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class="pcrb7t-"> a</span><span
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class="pcrb7t-"> -></span><span
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class="pcrb7t-"> a </span></td></tr></table> </div> <dd class="haddockdesc">
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Sometimes an external entity is a pure function, except that it passes arguments and/or results
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via pointers. The function <span
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class="pcrr7t-">unsafeLocalState </span>permits the packaging of such entities as pure
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functions.
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<p class="noindent"> The only IO operations allowed in the IO action passed to <span
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class="pcrr7t-">unsafeLocalState </span>are (a)
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local allocation (<span
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class="pcrr7t-">alloca</span>, <span
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class="pcrr7t-">allocaBytes </span>and derived operations such as <span
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class="pcrr7t-">withArray </span>and
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<span
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class="pcrr7t-">withCString</span>), and (b) pointer operations (<span
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class="pcrr7t-">Foreign.Storable </span>and <span
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class="pcrr7t-">Foreign.Ptr</span>) on the
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pointers to local storage, and (c) foreign functions whose only observable effect is to read and/or write
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the locally allocated memory. Passing an IO operation that does not obey these rules results in undefined
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behaviour.
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<p class="noindent"> It is expected that this operation will be replaced in a future revision of Haskell.
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</dl>
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