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<title>Data/Text/Encoding/Error.hs</title>
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<pre><a name="line-1"></a><span class='hs-comment'>{-# LANGUAGE CPP, DeriveDataTypeable #-}</span>
<a name="line-2"></a><span class='hs-comment'>-- |</span>
<a name="line-3"></a><span class='hs-comment'>-- Module : Data.Text.Encoding.Error</span>
<a name="line-4"></a><span class='hs-comment'>-- Copyright : (c) Bryan O'Sullivan 2009</span>
<a name="line-5"></a><span class='hs-comment'>--</span>
<a name="line-6"></a><span class='hs-comment'>-- License : BSD-style</span>
<a name="line-7"></a><span class='hs-comment'>-- Maintainer : bos@serpentine.com, rtomharper@googlemail.com,</span>
<a name="line-8"></a><span class='hs-comment'>-- duncan@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 : GHC</span>
<a name="line-11"></a><span class='hs-comment'>--</span>
<a name="line-12"></a><span class='hs-comment'>-- Types and functions for dealing with encoding and decoding errors</span>
<a name="line-13"></a><span class='hs-comment'>-- in Unicode text.</span>
<a name="line-14"></a><span class='hs-comment'>--</span>
<a name="line-15"></a><span class='hs-comment'>-- The standard functions for encoding and decoding text are strict,</span>
<a name="line-16"></a><span class='hs-comment'>-- which is to say that they throw exceptions on invalid input. This</span>
<a name="line-17"></a><span class='hs-comment'>-- is often unhelpful on real world input, so alternative functions</span>
<a name="line-18"></a><span class='hs-comment'>-- exist that accept custom handlers for dealing with invalid inputs.</span>
<a name="line-19"></a><span class='hs-comment'>-- These 'OnError' handlers are normal Haskell functions. You can use</span>
<a name="line-20"></a><span class='hs-comment'>-- one of the presupplied functions in this module, or you can write a</span>
<a name="line-21"></a><span class='hs-comment'>-- custom handler of your own.</span>
<a name="line-22"></a>
<a name="line-23"></a><span class='hs-keyword'>module</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>Text</span><span class='hs-varop'>.</span><span class='hs-conid'>Encoding</span><span class='hs-varop'>.</span><span class='hs-conid'>Error</span>
<a name="line-24"></a> <span class='hs-layout'>(</span>
<a name="line-25"></a> <span class='hs-comment'>-- * Error handling types</span>
<a name="line-26"></a> <span class='hs-conid'>UnicodeException</span><span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span>
<a name="line-27"></a> <span class='hs-layout'>,</span> <span class='hs-conid'>OnError</span>
<a name="line-28"></a> <span class='hs-layout'>,</span> <span class='hs-conid'>OnDecodeError</span>
<a name="line-29"></a> <span class='hs-layout'>,</span> <span class='hs-conid'>OnEncodeError</span>
<a name="line-30"></a> <span class='hs-comment'>-- * Useful error handling functions</span>
<a name="line-31"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>lenientDecode</span>
<a name="line-32"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>strictDecode</span>
<a name="line-33"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>strictEncode</span>
<a name="line-34"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>ignore</span>
<a name="line-35"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>replace</span>
<a name="line-36"></a> <span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-37"></a>
<a name="line-38"></a><span class='hs-cpp'>#if __GLASGOW_HASKELL__ >= 610</span>
<a name="line-39"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Exception</span> <span class='hs-layout'>(</span><span class='hs-conid'>Exception</span><span class='hs-layout'>,</span> <span class='hs-varid'>throw</span><span class='hs-layout'>)</span>
<a name="line-40"></a><span class='hs-cpp'>#else</span>
<a name="line-41"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Exception</span><span class='hs-varop'>.</span><span class='hs-conid'>Extensible</span> <span class='hs-layout'>(</span><span class='hs-conid'>Exception</span><span class='hs-layout'>,</span> <span class='hs-varid'>throw</span><span class='hs-layout'>)</span>
<a name="line-42"></a><span class='hs-cpp'>#endif</span>
<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> <span class='hs-layout'>(</span><span class='hs-conid'>Typeable</span><span class='hs-layout'>)</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'>Word</span> <span class='hs-layout'>(</span><span class='hs-conid'>Word8</span><span class='hs-layout'>)</span>
<a name="line-45"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Numeric</span> <span class='hs-layout'>(</span><span class='hs-varid'>showHex</span><span class='hs-layout'>)</span>
<a name="line-46"></a>
<a name="line-47"></a><a name="OnError"></a><span class='hs-comment'>-- | Function type for handling a coding error. It is supplied with</span>
<a name="line-48"></a><a name="OnError"></a><span class='hs-comment'>-- two inputs:</span>
<a name="line-49"></a><a name="OnError"></a><span class='hs-comment'>--</span>
<a name="line-50"></a><a name="OnError"></a><span class='hs-comment'>-- * A 'String' that describes the error.</span>
<a name="line-51"></a><a name="OnError"></a><span class='hs-comment'>--</span>
<a name="line-52"></a><a name="OnError"></a><span class='hs-comment'>-- * The input value that caused the error. If the error arose</span>
<a name="line-53"></a><a name="OnError"></a><span class='hs-comment'>-- because the end of input was reached or could not be identified</span>
<a name="line-54"></a><a name="OnError"></a><span class='hs-comment'>-- precisely, this value will be 'Nothing'.</span>
<a name="line-55"></a><a name="OnError"></a><span class='hs-comment'>--</span>
<a name="line-56"></a><a name="OnError"></a><span class='hs-comment'>-- If the handler returns a value wrapped with 'Just', that value will</span>
<a name="line-57"></a><a name="OnError"></a><span class='hs-comment'>-- be used in the output as the replacement for the invalid input. If</span>
<a name="line-58"></a><a name="OnError"></a><span class='hs-comment'>-- it returns 'Nothing', no value will be used in the output.</span>
<a name="line-59"></a><a name="OnError"></a><span class='hs-comment'>--</span>
<a name="line-60"></a><a name="OnError"></a><span class='hs-comment'>-- Should the handler need to abort processing, it should use 'error'</span>
<a name="line-61"></a><a name="OnError"></a><span class='hs-comment'>-- or 'throw' an exception (preferably a 'UnicodeException'). It may</span>
<a name="line-62"></a><a name="OnError"></a><span class='hs-comment'>-- use the description provided to construct a more helpful error</span>
<a name="line-63"></a><a name="OnError"></a><span class='hs-comment'>-- report.</span>
<a name="line-64"></a><a name="OnError"></a><span class='hs-keyword'>type</span> <span class='hs-conid'>OnError</span> <span class='hs-varid'>a</span> <span class='hs-varid'>b</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>String</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Maybe</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Maybe</span> <span class='hs-varid'>b</span>
<a name="line-65"></a>
<a name="line-66"></a><a name="OnDecodeError"></a><span class='hs-comment'>-- | A handler for a decoding error.</span>
<a name="line-67"></a><a name="OnDecodeError"></a><span class='hs-keyword'>type</span> <span class='hs-conid'>OnDecodeError</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>OnError</span> <span class='hs-conid'>Word8</span> <span class='hs-conid'>Char</span>
<a name="line-68"></a>
<a name="line-69"></a><a name="OnEncodeError"></a><span class='hs-comment'>-- | A handler for an encoding error.</span>
<a name="line-70"></a><a name="OnEncodeError"></a><span class='hs-keyword'>type</span> <span class='hs-conid'>OnEncodeError</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>OnError</span> <span class='hs-conid'>Char</span> <span class='hs-conid'>Word8</span>
<a name="line-71"></a>
<a name="line-72"></a><a name="UnicodeException"></a><span class='hs-comment'>-- | An exception type for representing Unicode encoding errors.</span>
<a name="line-73"></a><a name="UnicodeException"></a><span class='hs-keyword'>data</span> <span class='hs-conid'>UnicodeException</span> <span class='hs-keyglyph'>=</span>
<a name="line-74"></a> <span class='hs-conid'>DecodeError</span> <span class='hs-conid'>String</span> <span class='hs-layout'>(</span><span class='hs-conid'>Maybe</span> <span class='hs-conid'>Word8</span><span class='hs-layout'>)</span>
<a name="line-75"></a> <span class='hs-comment'>-- ^ Could not decode a byte sequence because it was invalid under</span>
<a name="line-76"></a> <span class='hs-comment'>-- the given encoding, or ran out of input in mid-decode.</span>
<a name="line-77"></a> <span class='hs-keyglyph'>|</span> <span class='hs-conid'>EncodeError</span> <span class='hs-conid'>String</span> <span class='hs-layout'>(</span><span class='hs-conid'>Maybe</span> <span class='hs-conid'>Char</span><span class='hs-layout'>)</span>
<a name="line-78"></a> <span class='hs-comment'>-- ^ Tried to encode a character that could not be represented</span>
<a name="line-79"></a> <span class='hs-comment'>-- under the given encoding, or ran out of input in mid-encode.</span>
<a name="line-80"></a> <span class='hs-keyword'>deriving</span> <span class='hs-layout'>(</span><span class='hs-conid'>Typeable</span><span class='hs-layout'>)</span>
<a name="line-81"></a>
<a name="line-82"></a><a name="showUnicodeException"></a><span class='hs-definition'>showUnicodeException</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>UnicodeException</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>String</span>
<a name="line-83"></a><span class='hs-definition'>showUnicodeException</span> <span class='hs-layout'>(</span><span class='hs-conid'>DecodeError</span> <span class='hs-varid'>desc</span> <span class='hs-layout'>(</span><span class='hs-conid'>Just</span> <span class='hs-varid'>w</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span>
<a name="line-84"></a> <span class='hs-keyglyph'>=</span> <span class='hs-str'>"Cannot decode byte '\\x"</span> <span class='hs-varop'>++</span> <span class='hs-varid'>showHex</span> <span class='hs-varid'>w</span> <span class='hs-layout'>(</span><span class='hs-str'>"': "</span> <span class='hs-varop'>++</span> <span class='hs-varid'>desc</span><span class='hs-layout'>)</span>
<a name="line-85"></a><span class='hs-definition'>showUnicodeException</span> <span class='hs-layout'>(</span><span class='hs-conid'>DecodeError</span> <span class='hs-varid'>desc</span> <span class='hs-conid'>Nothing</span><span class='hs-layout'>)</span>
<a name="line-86"></a> <span class='hs-keyglyph'>=</span> <span class='hs-str'>"Cannot decode input: "</span> <span class='hs-varop'>++</span> <span class='hs-varid'>desc</span>
<a name="line-87"></a><span class='hs-definition'>showUnicodeException</span> <span class='hs-layout'>(</span><span class='hs-conid'>EncodeError</span> <span class='hs-varid'>desc</span> <span class='hs-layout'>(</span><span class='hs-conid'>Just</span> <span class='hs-varid'>c</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span>
<a name="line-88"></a> <span class='hs-keyglyph'>=</span> <span class='hs-str'>"Cannot encode character '\\x"</span> <span class='hs-varop'>++</span> <span class='hs-varid'>showHex</span> <span class='hs-layout'>(</span><span class='hs-varid'>fromEnum</span> <span class='hs-varid'>c</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-str'>"': "</span> <span class='hs-varop'>++</span> <span class='hs-varid'>desc</span><span class='hs-layout'>)</span>
<a name="line-89"></a><span class='hs-definition'>showUnicodeException</span> <span class='hs-layout'>(</span><span class='hs-conid'>EncodeError</span> <span class='hs-varid'>desc</span> <span class='hs-conid'>Nothing</span><span class='hs-layout'>)</span>
<a name="line-90"></a> <span class='hs-keyglyph'>=</span> <span class='hs-str'>"Cannot encode input: "</span> <span class='hs-varop'>++</span> <span class='hs-varid'>desc</span>
<a name="line-91"></a>
<a name="line-92"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>Show</span> <span class='hs-conid'>UnicodeException</span> <span class='hs-keyword'>where</span>
<a name="line-93"></a> <span class='hs-varid'>show</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>showUnicodeException</span>
<a name="line-94"></a>
<a name="line-95"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>Exception</span> <span class='hs-conid'>UnicodeException</span>
<a name="line-96"></a>
<a name="line-97"></a><a name="strictDecode"></a><span class='hs-comment'>-- | Throw a 'UnicodeException' if decoding fails.</span>
<a name="line-98"></a><span class='hs-definition'>strictDecode</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>OnDecodeError</span>
<a name="line-99"></a><span class='hs-definition'>strictDecode</span> <span class='hs-varid'>desc</span> <span class='hs-varid'>c</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>throw</span> <span class='hs-layout'>(</span><span class='hs-conid'>DecodeError</span> <span class='hs-varid'>desc</span> <span class='hs-varid'>c</span><span class='hs-layout'>)</span>
<a name="line-100"></a>
<a name="line-101"></a><a name="lenientDecode"></a><span class='hs-comment'>-- | Replace an invalid input byte with the Unicode replacement</span>
<a name="line-102"></a><span class='hs-comment'>-- character U+FFFD.</span>
<a name="line-103"></a><span class='hs-definition'>lenientDecode</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>OnDecodeError</span>
<a name="line-104"></a><span class='hs-definition'>lenientDecode</span> <span class='hs-keyword'>_</span> <span class='hs-keyword'>_</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Just</span> <span class='hs-chr'>'\xfffd'</span>
<a name="line-105"></a>
<a name="line-106"></a><a name="strictEncode"></a><span class='hs-comment'>-- | Throw a 'UnicodeException' if encoding fails.</span>
<a name="line-107"></a><span class='hs-definition'>strictEncode</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>OnEncodeError</span>
<a name="line-108"></a><span class='hs-definition'>strictEncode</span> <span class='hs-varid'>desc</span> <span class='hs-varid'>c</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>throw</span> <span class='hs-layout'>(</span><span class='hs-conid'>EncodeError</span> <span class='hs-varid'>desc</span> <span class='hs-varid'>c</span><span class='hs-layout'>)</span>
<a name="line-109"></a>
<a name="line-110"></a><a name="ignore"></a><span class='hs-comment'>-- | Ignore an invalid input, substituting nothing in the output.</span>
<a name="line-111"></a><span class='hs-definition'>ignore</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>OnError</span> <span class='hs-varid'>a</span> <span class='hs-varid'>b</span>
<a name="line-112"></a><span class='hs-definition'>ignore</span> <span class='hs-keyword'>_</span> <span class='hs-keyword'>_</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Nothing</span>
<a name="line-113"></a>
<a name="line-114"></a><a name="replace"></a><span class='hs-comment'>-- | Replace an invalid input with a valid output.</span>
<a name="line-115"></a><span class='hs-definition'>replace</span> <span class='hs-keyglyph'>::</span> <span class='hs-varid'>b</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>OnError</span> <span class='hs-varid'>a</span> <span class='hs-varid'>b</span>
<a name="line-116"></a><span class='hs-definition'>replace</span> <span class='hs-varid'>c</span> <span class='hs-keyword'>_</span> <span class='hs-keyword'>_</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Just</span> <span class='hs-varid'>c</span>
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