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34 KiB
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808 lines
34 KiB
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<head><title>42 System.IO.Error</title>
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<meta name="date" content="2010-07-20 13:11:00" />
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</head><body
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>
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<!--l. 1--><div class="crosslinks"><p class="noindent">[<a
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href="haskellli3.html" >next</a>] [<a
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href="haskellch41.html" >prev</a>] [<a
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href="haskellch41.html#tailhaskellch41.html" >prev-tail</a>] [<a
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href="#tailhaskellch42.html">tail</a>] [<a
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href="haskellpa2.html#haskellch42.html" >up</a>] </p></div>
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<h2 class="chapterHead"><span class="titlemark">Chapter 42</span><br /><a
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id="x50-34100042"></a><span
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class="pcrr7t-">System.IO.Error</span></h2>
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<div class="quote">
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<div class="verbatim" id="verbatim-472">
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module System.IO.Error (
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 <br />    IOError,  userError,  mkIOError,  annotateIOError,  isAlreadyExistsError,
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 <br />    isDoesNotExistError,  isAlreadyInUseError,  isFullError,  isEOFError,
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 <br />    isIllegalOperation,  isPermissionError,  isUserError,  ioeGetErrorString,
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 <br />    ioeGetHandle,  ioeGetFileName,  IOErrorType,  alreadyExistsErrorType,
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 <br />    doesNotExistErrorType,  alreadyInUseErrorType,  fullErrorType,
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 <br />    eofErrorType,  illegalOperationErrorType,  permissionErrorType,
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 <br />    userErrorType,  ioError,  catch,  try
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 <br />  ) where
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</div>
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<p class="noindent"></div>
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<h3 class="sectionHead"><span class="titlemark">42.1 </span> <a
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id="x50-34200042.1"></a>I/O errors </h3>
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<p class="noindent">
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<dl> <dt class="haddockdesc">
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<!--tex4ht:inline--><div class="tabular"> <table id="TBL-697" class="tabular"
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cellspacing="0" cellpadding="0" rules="groups"
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><colgroup id="TBL-697-1g"><col
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id="TBL-697-1" /></colgroup><tr
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style="vertical-align:baseline;" id="TBL-697-1-"><td style="white-space:nowrap; text-align:left;" id="TBL-697-1-1"
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class="td11"><span
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class="pcrb7t-">type</span><span
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class="pcrb7t-"> IOError</span><span
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class="pcrb7t-"> =</span><span
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class="pcrb7t-"> IOError </span></td>
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</tr></table> </div> <dd class="haddockdesc">
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Errors of type <span
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class="pcrr7t-">IOError</span><a
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id="dx50-342001"></a> are used by the <span
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class="pcrr7t-">IO</span><a
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id="dx50-342002"></a> monad. This is an abstract type; the module
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<span
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class="pcrr7t-">System.IO.Error </span>provides functions to interrogate and construct values of type <span
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class="pcrr7t-">IOError</span><a
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id="dx50-342003"></a>.
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</dl>
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<p class="noindent">
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<dl> <dt class="haddockdesc">
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<!--tex4ht:inline--><div class="tabular"> <table id="TBL-698" class="tabular"
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cellspacing="0" cellpadding="0" rules="groups"
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><colgroup id="TBL-698-1g"><col
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id="TBL-698-1" /></colgroup><tr
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style="vertical-align:baseline;" id="TBL-698-1-"><td style="white-space:nowrap; text-align:left;" id="TBL-698-1-1"
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class="td11"><span
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class="pcrb7t-">userError</span><span
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class="pcrb7t-"> ::</span><span
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class="pcrb7t-"> String</span><span
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class="pcrb7t-"> -></span><span
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class="pcrb7t-"> IOError </span></td>
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</tr></table> </div> <dd class="haddockdesc">
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Construct an <span
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class="pcrr7t-">IOError</span><a
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id="dx50-342004"></a> value with a string describing the error. The <span
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class="pcrr7t-">fail</span><a
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id="dx50-342005"></a> method of the <span
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class="pcrr7t-">IO</span><a
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id="dx50-342006"></a> instance
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of the <span
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class="pcrr7t-">Monad</span><a
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id="dx50-342007"></a> class raises a <span
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class="pcrr7t-">userError</span><a
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id="dx50-342008"></a>, thus:
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<p class="noindent">
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<div class="quote">
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<div class="verbatim" id="verbatim-473">
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 instance Monad IO where
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 <br />   ...
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 <br />   fail s = ioError (userError s)
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</div>
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<p class="noindent"></div>
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</dl>
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<p class="noindent">
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<dl><dt class="haddockdesc">
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<!--tex4ht:inline--><div class="tabular"> <table id="TBL-699" class="tabular"
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cellspacing="0" cellpadding="0" rules="groups"
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><colgroup id="TBL-699-1g"><col
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id="TBL-699-1" /></colgroup><tr
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style="vertical-align:baseline;" id="TBL-699-1-"><td style="white-space:nowrap; text-align:left;" id="TBL-699-1-1"
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class="td11"><span
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class="pcrb7t-">mkIOError</span><span
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class="pcrb7t-"> ::</span><span
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class="pcrb7t-"> IOErrorType </span></td>
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</tr><tr
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style="vertical-align:baseline;" id="TBL-699-2-"><td style="white-space:nowrap; text-align:left;" id="TBL-699-2-1"
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class="td11"><span
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class="pcrb7t-"> </span><span
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class="pcrb7t-"> </span><span
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class="pcrb7t-"> </span><span
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class="pcrb7t-"> </span><span
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class="pcrb7t-"> </span><span
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class="pcrb7t-"> </span><span
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class="pcrb7t-"> </span><span
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class="pcrb7t-"> </span><span
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class="pcrb7t-"> </span><span
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class="pcrb7t-"> </span><span
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class="pcrb7t-"> </span><span
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class="pcrb7t-"> </span><span
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class="pcrb7t-"> -></span><span
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class="pcrb7t-"> String</span><span
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class="pcrb7t-"> -></span><span
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class="pcrb7t-"> Maybe</span><span
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class="pcrb7t-"> Handle</span><span
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class="pcrb7t-"> -></span><span
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class="pcrb7t-"> Maybe</span><span
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class="pcrb7t-"> FilePath</span><span
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class="pcrb7t-"> -></span><span
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class="pcrb7t-"> IOError </span></td>
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</tr></table> </div> <dd class="haddockdesc">
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Construct an <span
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class="pcrr7t-">IOError</span><a
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id="dx50-342009"></a> of the given type where the second argument describes the error location and
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the third and fourth argument contain the file handle and file path of the file involved in the error if
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applicable.
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</dl>
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<p class="noindent">
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<dl> <dt class="haddockdesc">
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<!--tex4ht:inline--><div class="tabular"> <table id="TBL-700" class="tabular"
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cellspacing="0" cellpadding="0" rules="groups"
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><colgroup id="TBL-700-1g"><col
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id="TBL-700-1" /></colgroup><tr
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style="vertical-align:baseline;" id="TBL-700-1-"><td style="white-space:nowrap; text-align:left;" id="TBL-700-1-1"
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class="td11"><span
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class="pcrb7t-">annotateIOError</span><span
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class="pcrb7t-"> ::</span><span
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class="pcrb7t-"> IOError </span></td>
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</tr><tr
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style="vertical-align:baseline;" id="TBL-700-2-"><td style="white-space:nowrap; text-align:left;" id="TBL-700-2-1"
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class="td11"><span
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class="pcrb7t-"> </span><span
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class="pcrb7t-"> </span><span
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class="pcrb7t-"> </span><span
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class="pcrb7t-"> </span><span
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class="pcrb7t-"> </span><span
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class="pcrb7t-"> </span><span
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class="pcrb7t-"> </span><span
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class="pcrb7t-"> </span><span
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class="pcrb7t-"> </span><span
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class="pcrb7t-"> </span><span
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class="pcrb7t-"> </span><span
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class="pcrb7t-"> </span><span
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class="pcrb7t-"> </span><span
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class="pcrb7t-"> </span><span
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class="pcrb7t-"> </span><span
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class="pcrb7t-"> </span><span
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class="pcrb7t-"> </span><span
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class="pcrb7t-"> </span><span
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class="pcrb7t-"> -></span><span
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class="pcrb7t-"> String</span><span
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class="pcrb7t-"> -></span><span
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class="pcrb7t-"> Maybe</span><span
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class="pcrb7t-"> Handle</span><span
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class="pcrb7t-"> -></span><span
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class="pcrb7t-"> Maybe</span><span
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class="pcrb7t-"> FilePath</span><span
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class="pcrb7t-"> -></span><span
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class="pcrb7t-"> IOError </span></td>
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</tr></table> </div> <dd class="haddockdesc">
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Adds a location description and maybe a file path and file handle to an <span
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class="pcrr7t-">IOError</span><a
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id="dx50-342010"></a>. If any of the file
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handle or file path is not given the corresponding value in the <span
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class="pcrr7t-">IOError</span><a
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id="dx50-342011"></a> remains unaltered.
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</dl>
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<p class="noindent">
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<h4 class="subsectionHead"><span class="titlemark">42.1.1 </span> <a
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id="x50-34300042.1.1"></a>Classifying I/O errors </h4>
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<p class="noindent">
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<dl> <dt class="haddockdesc">
|
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<!--tex4ht:inline--><div class="tabular"> <table id="TBL-701" class="tabular"
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cellspacing="0" cellpadding="0" rules="groups"
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><colgroup id="TBL-701-1g"><col
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id="TBL-701-1" /></colgroup><tr
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style="vertical-align:baseline;" id="TBL-701-1-"><td style="white-space:nowrap; text-align:left;" id="TBL-701-1-1"
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class="td11"><span
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class="pcrb7t-">isAlreadyExistsError</span><span
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class="pcrb7t-"> ::</span><span
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class="pcrb7t-"> IOError</span><span
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class="pcrb7t-"> -></span><span
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class="pcrb7t-"> Bool </span></td>
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</tr></table> </div> <dd class="haddockdesc">
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An error indicating that an <span
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class="pcrr7t-">IO</span><a
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id="dx50-343001"></a> operation failed because one of its arguments already exists.
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</dl>
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<p class="noindent">
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<dl> <dt class="haddockdesc">
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<!--tex4ht:inline--><div class="tabular"> <table id="TBL-702" class="tabular"
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cellspacing="0" cellpadding="0" rules="groups"
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><colgroup id="TBL-702-1g"><col
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id="TBL-702-1" /></colgroup><tr
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style="vertical-align:baseline;" id="TBL-702-1-"><td style="white-space:nowrap; text-align:left;" id="TBL-702-1-1"
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class="td11"><span
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class="pcrb7t-">isDoesNotExistError</span><span
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class="pcrb7t-"> ::</span><span
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class="pcrb7t-"> IOError</span><span
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class="pcrb7t-"> -></span><span
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class="pcrb7t-"> Bool </span></td></tr></table> </div> <dd class="haddockdesc">
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An error indicating that an <span
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class="pcrr7t-">IO</span><a
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id="dx50-343002"></a> operation failed because one of its arguments does not exist.
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</dl>
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<p class="noindent">
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<dl> <dt class="haddockdesc">
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<!--tex4ht:inline--><div class="tabular"> <table id="TBL-703" class="tabular"
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cellspacing="0" cellpadding="0" rules="groups"
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><colgroup id="TBL-703-1g"><col
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id="TBL-703-1" /></colgroup><tr
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style="vertical-align:baseline;" id="TBL-703-1-"><td style="white-space:nowrap; text-align:left;" id="TBL-703-1-1"
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class="td11"><span
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class="pcrb7t-">isAlreadyInUseError</span><span
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class="pcrb7t-"> ::</span><span
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class="pcrb7t-"> IOError</span><span
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class="pcrb7t-"> -></span><span
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class="pcrb7t-"> Bool </span></td>
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</tr></table> </div> <dd class="haddockdesc">
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An error indicating that an <span
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class="pcrr7t-">IO</span><a
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id="dx50-343003"></a> operation failed because one of its arguments is a single-use resource,
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which is already being used (for example, opening the same file twice for writing might give this
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error).
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</dl>
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<p class="noindent">
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<dl> <dt class="haddockdesc">
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<!--tex4ht:inline--><div class="tabular"> <table id="TBL-704" class="tabular"
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cellspacing="0" cellpadding="0" rules="groups"
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><colgroup id="TBL-704-1g"><col
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id="TBL-704-1" /></colgroup><tr
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style="vertical-align:baseline;" id="TBL-704-1-"><td style="white-space:nowrap; text-align:left;" id="TBL-704-1-1"
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class="td11"><span
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class="pcrb7t-">isFullError</span><span
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class="pcrb7t-"> ::</span><span
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class="pcrb7t-"> IOError</span><span
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class="pcrb7t-"> -></span><span
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class="pcrb7t-"> Bool </span></td></tr></table> </div> <dd class="haddockdesc">
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An error indicating that an <span
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class="pcrr7t-">IO</span><a
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id="dx50-343004"></a> operation failed because the device is full.
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</dl>
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<p class="noindent">
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<dl> <dt class="haddockdesc">
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|
<!--tex4ht:inline--><div class="tabular"> <table id="TBL-705" class="tabular"
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cellspacing="0" cellpadding="0" rules="groups"
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><colgroup id="TBL-705-1g"><col
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id="TBL-705-1" /></colgroup><tr
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style="vertical-align:baseline;" id="TBL-705-1-"><td style="white-space:nowrap; text-align:left;" id="TBL-705-1-1"
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class="td11"><span
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class="pcrb7t-">isEOFError</span><span
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class="pcrb7t-"> ::</span><span
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class="pcrb7t-"> IOError</span><span
|
|
class="pcrb7t-"> -></span><span
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class="pcrb7t-"> Bool </span></td></tr></table> </div> <dd class="haddockdesc">
|
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An error indicating that an <span
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class="pcrr7t-">IO</span><a
|
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id="dx50-343005"></a> operation failed because the end of file has been reached.
|
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</dl>
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<p class="noindent">
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<dl> <dt class="haddockdesc">
|
|
<!--tex4ht:inline--><div class="tabular"> <table id="TBL-706" class="tabular"
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cellspacing="0" cellpadding="0" rules="groups"
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><colgroup id="TBL-706-1g"><col
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id="TBL-706-1" /></colgroup><tr
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style="vertical-align:baseline;" id="TBL-706-1-"><td style="white-space:nowrap; text-align:left;" id="TBL-706-1-1"
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class="td11"><span
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|
class="pcrb7t-">isIllegalOperation</span><span
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class="pcrb7t-"> ::</span><span
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class="pcrb7t-"> IOError</span><span
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|
class="pcrb7t-"> -></span><span
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|
class="pcrb7t-"> Bool </span></td>
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</tr></table> </div> <dd class="haddockdesc">
|
|
An error indicating that an <span
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|
class="pcrr7t-">IO</span><a
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id="dx50-343006"></a> operation failed because the operation was not possible. Any
|
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computation which returns an <span
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class="pcrr7t-">IO</span><a
|
|
id="dx50-343007"></a> result may fail with <span
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class="pcrr7t-">isIllegalOperation</span><a
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|
id="dx50-343008"></a>. In some cases, an
|
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implementation will not be able to distinguish between the possible error causes. In this case it should
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fail with <span
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class="pcrr7t-">isIllegalOperation</span><a
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id="dx50-343009"></a>.
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</dl>
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<p class="noindent">
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<dl> <dt class="haddockdesc">
|
|
<!--tex4ht:inline--><div class="tabular"> <table id="TBL-707" class="tabular"
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cellspacing="0" cellpadding="0" rules="groups"
|
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><colgroup id="TBL-707-1g"><col
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id="TBL-707-1" /></colgroup><tr
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style="vertical-align:baseline;" id="TBL-707-1-"><td style="white-space:nowrap; text-align:left;" id="TBL-707-1-1"
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class="td11"><span
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|
class="pcrb7t-">isPermissionError</span><span
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class="pcrb7t-"> ::</span><span
|
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class="pcrb7t-"> IOError</span><span
|
|
class="pcrb7t-"> -></span><span
|
|
class="pcrb7t-"> Bool </span></td></tr></table> </div> <dd class="haddockdesc">
|
|
An error indicating that an <span
|
|
class="pcrr7t-">IO</span><a
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id="dx50-343010"></a> operation failed because the user does not have sufficient operating
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system privilege to perform that operation.
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</dl>
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<p class="noindent">
|
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<dl> <dt class="haddockdesc">
|
|
<!--tex4ht:inline--><div class="tabular"> <table id="TBL-708" class="tabular"
|
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cellspacing="0" cellpadding="0" rules="groups"
|
|
><colgroup id="TBL-708-1g"><col
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id="TBL-708-1" /></colgroup><tr
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style="vertical-align:baseline;" id="TBL-708-1-"><td style="white-space:nowrap; text-align:left;" id="TBL-708-1-1"
|
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class="td11"><span
|
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class="pcrb7t-">isUserError</span><span
|
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class="pcrb7t-"> ::</span><span
|
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class="pcrb7t-"> IOError</span><span
|
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class="pcrb7t-"> -></span><span
|
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class="pcrb7t-"> Bool </span></td></tr></table> </div> <dd class="haddockdesc">
|
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A programmer-defined error value constructed using <span
|
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class="pcrr7t-">userError</span><a
|
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id="dx50-343011"></a>.
|
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</dl>
|
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|
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<p class="noindent">
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<h4 class="subsectionHead"><span class="titlemark">42.1.2 </span> <a
|
|
id="x50-34400042.1.2"></a>Attributes of I/O errors </h4>
|
|
<p class="noindent">
|
|
<dl> <dt class="haddockdesc">
|
|
<span
|
|
class="pcrb7t-">ioeGetErrorString</span><span
|
|
class="pcrb7t-"> ::</span><span
|
|
class="pcrb7t-"> IOError</span><span
|
|
class="pcrb7t-"> -></span><span
|
|
class="pcrb7t-"> String</span> <dd class="haddockdesc">
|
|
<dt class="haddockdesc">
|
|
<span
|
|
class="pcrb7t-">ioeGetHandle</span><span
|
|
class="pcrb7t-"> ::</span><span
|
|
class="pcrb7t-"> IOError</span><span
|
|
class="pcrb7t-"> -></span><span
|
|
class="pcrb7t-"> Maybe</span><span
|
|
class="pcrb7t-"> Handle</span> <dd class="haddockdesc">
|
|
<dt class="haddockdesc">
|
|
<span
|
|
class="pcrb7t-">ioeGetFileName</span><span
|
|
class="pcrb7t-"> ::</span><span
|
|
class="pcrb7t-"> IOError</span><span
|
|
class="pcrb7t-"> -></span><span
|
|
class="pcrb7t-"> Maybe</span><span
|
|
class="pcrb7t-"> FilePath</span> <dd class="haddockdesc"></dl>
|
|
<p class="noindent">
|
|
<h3 class="sectionHead"><span class="titlemark">42.2 </span> <a
|
|
id="x50-34500042.2"></a>Types of I/O error </h3>
|
|
<p class="noindent">
|
|
<dl> <dt class="haddockdesc">
|
|
<!--tex4ht:inline--><div class="tabular"> <table id="TBL-709" class="tabular"
|
|
cellspacing="0" cellpadding="0" rules="groups"
|
|
><colgroup id="TBL-709-1g"><col
|
|
id="TBL-709-1" /></colgroup><tr
|
|
style="vertical-align:baseline;" id="TBL-709-1-"><td style="white-space:nowrap; text-align:left;" id="TBL-709-1-1"
|
|
class="td11"><span
|
|
class="pcrb7t-">data</span><span
|
|
class="pcrb7t-"> IOErrorType </span></td>
|
|
</tr></table> </div> <dd class="haddockdesc">
|
|
An abstract type that contains a value for each variant of <span
|
|
class="pcrr7t-">IOError</span><a
|
|
id="dx50-345001"></a>.
|
|
</dl>
|
|
<p class="noindent">
|
|
<dl> <dt class="haddockdesc">
|
|
<!--tex4ht:inline--><div class="tabular"> <table id="TBL-710" class="tabular"
|
|
cellspacing="0" cellpadding="0" rules="groups"
|
|
><colgroup id="TBL-710-1g"><col
|
|
id="TBL-710-1" /></colgroup><tr
|
|
style="vertical-align:baseline;" id="TBL-710-1-"><td style="white-space:nowrap; text-align:left;" id="TBL-710-1-1"
|
|
class="td11"><span
|
|
class="pcrb7t-">instance</span><span
|
|
class="pcrb7t-"> Eq</span><span
|
|
class="pcrb7t-"> IOErrorType </span></td>
|
|
</tr><tr
|
|
style="vertical-align:baseline;" id="TBL-710-2-"><td style="white-space:nowrap; text-align:left;" id="TBL-710-2-1"
|
|
class="td11"><span
|
|
class="pcrb7t-">instance</span><span
|
|
class="pcrb7t-"> Show</span><span
|
|
class="pcrb7t-"> IOErrorType </span></td>
|
|
</tr></table> </div> <dd class="haddockdesc">
|
|
</dl>
|
|
<p class="noindent">
|
|
<dl><dt class="haddockdesc">
|
|
<!--tex4ht:inline--><div class="tabular"> <table id="TBL-711" class="tabular"
|
|
cellspacing="0" cellpadding="0" rules="groups"
|
|
><colgroup id="TBL-711-1g"><col
|
|
id="TBL-711-1" /></colgroup><tr
|
|
style="vertical-align:baseline;" id="TBL-711-1-"><td style="white-space:nowrap; text-align:left;" id="TBL-711-1-1"
|
|
class="td11"><span
|
|
class="pcrb7t-">alreadyExistsErrorType</span><span
|
|
class="pcrb7t-"> ::</span><span
|
|
class="pcrb7t-"> IOErrorType </span></td>
|
|
</tr></table> </div> <dd class="haddockdesc">
|
|
I/O error where the operation failed because one of its arguments already exists.
|
|
</dl>
|
|
<p class="noindent">
|
|
<dl> <dt class="haddockdesc">
|
|
<!--tex4ht:inline--><div class="tabular"> <table id="TBL-712" class="tabular"
|
|
cellspacing="0" cellpadding="0" rules="groups"
|
|
><colgroup id="TBL-712-1g"><col
|
|
id="TBL-712-1" /></colgroup><tr
|
|
style="vertical-align:baseline;" id="TBL-712-1-"><td style="white-space:nowrap; text-align:left;" id="TBL-712-1-1"
|
|
class="td11"><span
|
|
class="pcrb7t-">doesNotExistErrorType</span><span
|
|
class="pcrb7t-"> ::</span><span
|
|
class="pcrb7t-"> IOErrorType </span></td>
|
|
</tr></table> </div> <dd class="haddockdesc">
|
|
I/O error where the operation failed because one of its arguments does not exist.
|
|
</dl>
|
|
|
|
|
|
|
|
<p class="noindent">
|
|
<dl> <dt class="haddockdesc">
|
|
<!--tex4ht:inline--><div class="tabular"> <table id="TBL-713" class="tabular"
|
|
cellspacing="0" cellpadding="0" rules="groups"
|
|
><colgroup id="TBL-713-1g"><col
|
|
id="TBL-713-1" /></colgroup><tr
|
|
style="vertical-align:baseline;" id="TBL-713-1-"><td style="white-space:nowrap; text-align:left;" id="TBL-713-1-1"
|
|
class="td11"><span
|
|
class="pcrb7t-">alreadyInUseErrorType</span><span
|
|
class="pcrb7t-"> ::</span><span
|
|
class="pcrb7t-"> IOErrorType </span></td>
|
|
</tr></table> </div> <dd class="haddockdesc">
|
|
I/O error where the operation failed because one of its arguments is a single-use resource, which is
|
|
already being used.
|
|
</dl>
|
|
<p class="noindent">
|
|
<dl> <dt class="haddockdesc">
|
|
<!--tex4ht:inline--><div class="tabular"> <table id="TBL-714" class="tabular"
|
|
cellspacing="0" cellpadding="0" rules="groups"
|
|
><colgroup id="TBL-714-1g"><col
|
|
id="TBL-714-1" /></colgroup><tr
|
|
style="vertical-align:baseline;" id="TBL-714-1-"><td style="white-space:nowrap; text-align:left;" id="TBL-714-1-1"
|
|
class="td11"><span
|
|
class="pcrb7t-">fullErrorType</span><span
|
|
class="pcrb7t-"> ::</span><span
|
|
class="pcrb7t-"> IOErrorType </span></td>
|
|
</tr></table> </div> <dd class="haddockdesc">
|
|
I/O error where the operation failed because the device is full.
|
|
</dl>
|
|
<p class="noindent">
|
|
<dl> <dt class="haddockdesc">
|
|
<!--tex4ht:inline--><div class="tabular"> <table id="TBL-715" class="tabular"
|
|
cellspacing="0" cellpadding="0" rules="groups"
|
|
><colgroup id="TBL-715-1g"><col
|
|
id="TBL-715-1" /></colgroup><tr
|
|
style="vertical-align:baseline;" id="TBL-715-1-"><td style="white-space:nowrap; text-align:left;" id="TBL-715-1-1"
|
|
class="td11"><span
|
|
class="pcrb7t-">eofErrorType</span><span
|
|
class="pcrb7t-"> ::</span><span
|
|
class="pcrb7t-"> IOErrorType </span></td>
|
|
</tr></table> </div> <dd class="haddockdesc">
|
|
I/O error where the operation failed because the end of file has been reached.
|
|
</dl>
|
|
<p class="noindent">
|
|
<dl> <dt class="haddockdesc">
|
|
<!--tex4ht:inline--><div class="tabular"> <table id="TBL-716" class="tabular"
|
|
cellspacing="0" cellpadding="0" rules="groups"
|
|
><colgroup id="TBL-716-1g"><col
|
|
id="TBL-716-1" /></colgroup><tr
|
|
style="vertical-align:baseline;" id="TBL-716-1-"><td style="white-space:nowrap; text-align:left;" id="TBL-716-1-1"
|
|
class="td11"><span
|
|
class="pcrb7t-">illegalOperationErrorType</span><span
|
|
class="pcrb7t-"> ::</span><span
|
|
class="pcrb7t-"> IOErrorType </span></td>
|
|
</tr></table> </div> <dd class="haddockdesc">
|
|
I/O error where the operation is not possible.
|
|
</dl>
|
|
<p class="noindent">
|
|
<dl> <dt class="haddockdesc">
|
|
<!--tex4ht:inline--><div class="tabular"> <table id="TBL-717" class="tabular"
|
|
cellspacing="0" cellpadding="0" rules="groups"
|
|
><colgroup id="TBL-717-1g"><col
|
|
id="TBL-717-1" /></colgroup><tr
|
|
style="vertical-align:baseline;" id="TBL-717-1-"><td style="white-space:nowrap; text-align:left;" id="TBL-717-1-1"
|
|
class="td11"><span
|
|
class="pcrb7t-">permissionErrorType</span><span
|
|
class="pcrb7t-"> ::</span><span
|
|
class="pcrb7t-"> IOErrorType </span></td>
|
|
</tr></table> </div> <dd class="haddockdesc">
|
|
I/O error where the operation failed because the user does not have sufficient operating system
|
|
privilege to perform that operation.
|
|
</dl>
|
|
<p class="noindent">
|
|
<dl> <dt class="haddockdesc">
|
|
<!--tex4ht:inline--><div class="tabular"> <table id="TBL-718" class="tabular"
|
|
cellspacing="0" cellpadding="0" rules="groups"
|
|
><colgroup id="TBL-718-1g"><col
|
|
id="TBL-718-1" /></colgroup><tr
|
|
style="vertical-align:baseline;" id="TBL-718-1-"><td style="white-space:nowrap; text-align:left;" id="TBL-718-1-1"
|
|
class="td11"><span
|
|
class="pcrb7t-">userErrorType</span><span
|
|
class="pcrb7t-"> ::</span><span
|
|
class="pcrb7t-"> IOErrorType </span></td>
|
|
</tr></table> </div> <dd class="haddockdesc">
|
|
I/O error that is programmer-defined.
|
|
</dl>
|
|
|
|
|
|
|
|
<p class="noindent">
|
|
<h3 class="sectionHead"><span class="titlemark">42.3 </span> <a
|
|
id="x50-34600042.3"></a>Throwing and catching I/O errors </h3>
|
|
<p class="noindent">
|
|
<dl> <dt class="haddockdesc">
|
|
<!--tex4ht:inline--><div class="tabular"> <table id="TBL-719" class="tabular"
|
|
cellspacing="0" cellpadding="0" rules="groups"
|
|
><colgroup id="TBL-719-1g"><col
|
|
id="TBL-719-1" /></colgroup><tr
|
|
style="vertical-align:baseline;" id="TBL-719-1-"><td style="white-space:nowrap; text-align:left;" id="TBL-719-1-1"
|
|
class="td11"><span
|
|
class="pcrb7t-">ioError</span><span
|
|
class="pcrb7t-"> ::</span><span
|
|
class="pcrb7t-"> IOError</span><span
|
|
class="pcrb7t-"> -></span><span
|
|
class="pcrb7t-"> IO</span><span
|
|
class="pcrb7t-"> a </span></td></tr></table> </div> <dd class="haddockdesc">
|
|
Raise an <span
|
|
class="pcrr7t-">IOError</span><a
|
|
id="dx50-346001"></a> in the <span
|
|
class="pcrr7t-">IO</span><a
|
|
id="dx50-346002"></a> monad.
|
|
</dl>
|
|
<p class="noindent">
|
|
<dl> <dt class="haddockdesc">
|
|
<!--tex4ht:inline--><div class="tabular"> <table id="TBL-720" class="tabular"
|
|
cellspacing="0" cellpadding="0" rules="groups"
|
|
><colgroup id="TBL-720-1g"><col
|
|
id="TBL-720-1" /></colgroup><tr
|
|
style="vertical-align:baseline;" id="TBL-720-1-"><td style="white-space:nowrap; text-align:left;" id="TBL-720-1-1"
|
|
class="td11"><span
|
|
class="pcrb7t-">catch</span><span
|
|
class="pcrb7t-"> ::</span><span
|
|
class="pcrb7t-"> IO</span><span
|
|
class="pcrb7t-"> a</span><span
|
|
class="pcrb7t-"> -></span><span
|
|
class="pcrb7t-"> (IOError</span><span
|
|
class="pcrb7t-"> -></span><span
|
|
class="pcrb7t-"> IO</span><span
|
|
class="pcrb7t-"> a)</span><span
|
|
class="pcrb7t-"> -></span><span
|
|
class="pcrb7t-"> IO</span><span
|
|
class="pcrb7t-"> a </span></td>
|
|
</tr></table> </div> <dd class="haddockdesc">
|
|
The <span
|
|
class="pcrr7t-">catch</span><a
|
|
id="dx50-346003"></a> function establishes a handler that receives any <span
|
|
class="pcrr7t-">IOError</span><a
|
|
id="dx50-346004"></a> raised in the action protected
|
|
by <span
|
|
class="pcrr7t-">catch</span><a
|
|
id="dx50-346005"></a>. An <span
|
|
class="pcrr7t-">IOError</span><a
|
|
id="dx50-346006"></a> is caught by the most recent handler established by <span
|
|
class="pcrr7t-">catch</span><a
|
|
id="dx50-346007"></a>. These handlers
|
|
are not selective: all <span
|
|
class="pcrr7t-">IOError</span><a
|
|
id="dx50-346008"></a>s are caught. Exception propagation must be explicitly provided in a
|
|
handler by re-raising any unwanted exceptions. For example, in
|
|
<p class="noindent">
|
|
<div class="quote">
|
|
|
|
|
|
|
|
<div class="verbatim" id="verbatim-474">
|
|
 f = catch g (\e -> if IO.isEOFError e then return [] else ioError e)
|
|
</div>
|
|
<p class="noindent"></div>
|
|
<p class="noindent"> the function <span
|
|
class="pcrr7t-">f </span>returns <span
|
|
class="pcrr7t-">[] </span>when an end-of-file exception (cf. <span
|
|
class="pcrr7t-">isEOFError</span><a
|
|
id="dx50-346009"></a>) occurs in <span
|
|
class="pcrr7t-">g</span>; otherwise, the
|
|
exception is propagated to the next outer handler.
|
|
<p class="noindent"> When an exception propagates outside the main program, the Haskell system prints the associated <span
|
|
class="pcrr7t-">IOError</span><a
|
|
id="dx50-346010"></a>
|
|
value and exits the program.
|
|
</dl>
|
|
<p class="noindent">
|
|
<dl> <dt class="haddockdesc">
|
|
<!--tex4ht:inline--><div class="tabular"> <table id="TBL-721" class="tabular"
|
|
cellspacing="0" cellpadding="0" rules="groups"
|
|
><colgroup id="TBL-721-1g"><col
|
|
id="TBL-721-1" /></colgroup><tr
|
|
style="vertical-align:baseline;" id="TBL-721-1-"><td style="white-space:nowrap; text-align:left;" id="TBL-721-1-1"
|
|
class="td11"><span
|
|
class="pcrb7t-">try</span><span
|
|
class="pcrb7t-"> ::</span><span
|
|
class="pcrb7t-"> IO</span><span
|
|
class="pcrb7t-"> a</span><span
|
|
class="pcrb7t-"> -></span><span
|
|
class="pcrb7t-"> IO</span><span
|
|
class="pcrb7t-"> (Either</span><span
|
|
class="pcrb7t-"> IOError</span><span
|
|
class="pcrb7t-"> a) </span></td>
|
|
</tr></table> </div> <dd class="haddockdesc">
|
|
The construct <span
|
|
class="pcrr7t-">try</span><a
|
|
id="dx50-346011"></a><span
|
|
class="pcrr7t-">comp </span>exposes IO errors which occur within a computation, and which are not fully
|
|
handled.
|
|
</dl>
|
|
|
|
|
|
|
|
<a
|
|
id="dx50-346012"></a>
|
|
<a
|
|
id="dx50-346013"></a>
|
|
<a
|
|
id="dx50-346014"></a>
|
|
<a
|
|
id="dx50-346015"></a>
|
|
<a
|
|
id="dx50-346016"></a>
|
|
<a
|
|
id="dx50-346017"></a>
|
|
<a
|
|
id="dx50-346018"></a>
|
|
<a
|
|
id="dx50-346019"></a>
|
|
<a
|
|
id="dx50-346020"></a>
|
|
<a
|
|
id="dx50-346021"></a>
|
|
<a
|
|
id="dx50-346022"></a>
|
|
<a
|
|
id="dx50-346023"></a>
|
|
<a
|
|
id="dx50-346024"></a>
|
|
<a
|
|
id="dx50-346025"></a>
|
|
<a
|
|
id="dx50-346026"></a>
|
|
<a
|
|
id="dx50-346027"></a>
|
|
<a
|
|
id="dx50-346028"></a>
|
|
<a
|
|
id="dx50-346029"></a>
|
|
<a
|
|
id="dx50-346030"></a>
|
|
<a
|
|
id="dx50-346031"></a>
|
|
<a
|
|
id="dx50-346032"></a>
|
|
<a
|
|
id="dx50-346033"></a>
|
|
<a
|
|
id="dx50-346034"></a>
|
|
<a
|
|
id="dx50-346035"></a>
|
|
<a
|
|
id="dx50-346036"></a>
|
|
<a
|
|
id="dx50-346037"></a>
|
|
<a
|
|
id="dx50-346038"></a>
|
|
<a
|
|
id="dx50-346039"></a>
|
|
<a
|
|
id="dx50-346040"></a>
|
|
<a
|
|
id="dx50-346041"></a>
|
|
<a
|
|
id="dx50-346042"></a>
|
|
<a
|
|
id="dx50-346043"></a>
|
|
<a
|
|
id="dx50-346044"></a>
|
|
<a
|
|
id="dx50-346045"></a>
|
|
<a
|
|
id="dx50-346046"></a>
|
|
<a
|
|
id="dx50-346047"></a>
|
|
<a
|
|
id="dx50-346048"></a>
|
|
<a
|
|
id="dx50-346049"></a>
|
|
<a
|
|
id="dx50-346050"></a>
|
|
<a
|
|
id="dx50-346051"></a>
|
|
<a
|
|
id="dx50-346052"></a>
|
|
<a
|
|
id="dx50-346053"></a>
|
|
<a
|
|
id="dx50-346054"></a>
|
|
<a
|
|
id="dx50-346055"></a>
|
|
<a
|
|
id="dx50-346056"></a>
|
|
<a
|
|
id="dx50-346057"></a>
|
|
<a
|
|
id="dx50-346058"></a>
|
|
<a
|
|
id="dx50-346059"></a>
|
|
<a
|
|
id="dx50-346060"></a>
|
|
<a
|
|
id="dx50-346061"></a>
|
|
<a
|
|
id="dx50-346062"></a>
|
|
|
|
|
|
|
|
<a
|
|
id="dx50-346063"></a>
|
|
<a
|
|
id="dx50-346064"></a>
|
|
<a
|
|
id="dx50-346065"></a>
|
|
<a
|
|
id="dx50-346066"></a>
|
|
<a
|
|
id="dx50-346067"></a>
|
|
<a
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