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<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 : Debug.Trace</span>
<a name="line-4"></a><span class='hs-comment'>-- Copyright : (c) The University of Glasgow 2001</span>
<a name="line-5"></a><span class='hs-comment'>-- License : BSD-style (see the file libraries/base/LICENSE)</span>
<a name="line-6"></a><span class='hs-comment'>-- </span>
<a name="line-7"></a><span class='hs-comment'>-- Maintainer : libraries@haskell.org</span>
<a name="line-8"></a><span class='hs-comment'>-- Stability : provisional</span>
<a name="line-9"></a><span class='hs-comment'>-- Portability : portable</span>
<a name="line-10"></a><span class='hs-comment'>--</span>
<a name="line-11"></a><span class='hs-comment'>-- The 'trace' function.</span>
<a name="line-12"></a><span class='hs-comment'>--</span>
<a name="line-13"></a><span class='hs-comment'>-----------------------------------------------------------------------------</span>
<a name="line-14"></a>
<a name="line-15"></a><span class='hs-keyword'>module</span> <span class='hs-conid'>Debug</span><span class='hs-varop'>.</span><span class='hs-conid'>Trace</span> <span class='hs-layout'>(</span>
<a name="line-16"></a> <span class='hs-comment'>-- * Tracing</span>
<a name="line-17"></a> <span class='hs-varid'>putTraceMsg</span><span class='hs-layout'>,</span> <span class='hs-comment'>-- :: String -> IO ()</span>
<a name="line-18"></a> <span class='hs-varid'>trace</span><span class='hs-layout'>,</span> <span class='hs-comment'>-- :: String -> a -> a</span>
<a name="line-19"></a> <span class='hs-varid'>traceShow</span>
<a name="line-20"></a> <span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-21"></a>
<a name="line-22"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Prelude</span>
<a name="line-23"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>System</span><span class='hs-varop'>.</span><span class='hs-conid'>IO</span><span class='hs-varop'>.</span><span class='hs-conid'>Unsafe</span>
<a name="line-24"></a>
<a name="line-25"></a><span class='hs-cpp'>#ifdef __GLASGOW_HASKELL__</span>
<a name="line-26"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Foreign</span><span class='hs-varop'>.</span><span class='hs-conid'>C</span><span class='hs-varop'>.</span><span class='hs-conid'>String</span>
<a name="line-27"></a><span class='hs-cpp'>#else</span>
<a name="line-28"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>System</span><span class='hs-varop'>.</span><span class='hs-conid'>IO</span> <span class='hs-layout'>(</span><span class='hs-varid'>hPutStrLn</span><span class='hs-layout'>,</span><span class='hs-varid'>stderr</span><span class='hs-layout'>)</span>
<a name="line-29"></a><span class='hs-cpp'>#endif</span>
<a name="line-30"></a>
<a name="line-31"></a><a name="putTraceMsg"></a><span class='hs-comment'>-- | 'putTraceMsg' function outputs the trace message from IO monad.</span>
<a name="line-32"></a><span class='hs-comment'>-- Usually the output stream is 'System.IO.stderr' but if the function is called</span>
<a name="line-33"></a><span class='hs-comment'>-- from Windows GUI application then the output will be directed to the Windows</span>
<a name="line-34"></a><span class='hs-comment'>-- debug console.</span>
<a name="line-35"></a><span class='hs-definition'>putTraceMsg</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>String</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>IO</span> <span class='hs-conid'>()</span>
<a name="line-36"></a><span class='hs-definition'>putTraceMsg</span> <span class='hs-varid'>msg</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-37"></a><span class='hs-cpp'>#ifndef __GLASGOW_HASKELL__</span>
<a name="line-38"></a> <span class='hs-varid'>hPutStrLn</span> <span class='hs-varid'>stderr</span> <span class='hs-varid'>msg</span>
<a name="line-39"></a><span class='hs-cpp'>#else</span>
<a name="line-40"></a> <span class='hs-varid'>withCString</span> <span class='hs-str'>"%s\n"</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>cfmt</span> <span class='hs-keyglyph'>-></span>
<a name="line-41"></a> <span class='hs-varid'>withCString</span> <span class='hs-varid'>msg</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>cmsg</span> <span class='hs-keyglyph'>-></span>
<a name="line-42"></a> <span class='hs-varid'>debugBelch</span> <span class='hs-varid'>cfmt</span> <span class='hs-varid'>cmsg</span>
<a name="line-43"></a>
<a name="line-44"></a><span class='hs-comment'>-- don't use debugBelch() directly, because we cannot call varargs functions</span>
<a name="line-45"></a><span class='hs-comment'>-- using the FFI.</span>
<a name="line-46"></a><span class='hs-keyword'>foreign</span> <span class='hs-keyword'>import</span> <span class='hs-keyword'>ccall</span> <span class='hs-keyword'>unsafe</span> <span class='hs-str'>"HsBase.h debugBelch2"</span>
<a name="line-47"></a> <span class='hs-varid'>debugBelch</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>CString</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>CString</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>IO</span> <span class='hs-conid'>()</span>
<a name="line-48"></a><span class='hs-cpp'>#endif</span>
<a name="line-49"></a>
<a name="line-50"></a><a name="trace"></a><span class='hs-comment'>{-# NOINLINE trace #-}</span>
<a name="line-51"></a><span class='hs-comment'>{-|
<a name="line-52"></a>When called, 'trace' outputs the string in its first argument, before
<a name="line-53"></a>returning the second argument as its result. The 'trace' function is not
<a name="line-54"></a>referentially transparent, and should only be used for debugging, or for
<a name="line-55"></a>monitoring execution. Some implementations of 'trace' may decorate the string
<a name="line-56"></a>that\'s output to indicate that you\'re tracing. The function is implemented on
<a name="line-57"></a>top of 'putTraceMsg'.
<a name="line-58"></a>-}</span>
<a name="line-59"></a><span class='hs-definition'>trace</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>String</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a</span>
<a name="line-60"></a><span class='hs-definition'>trace</span> <span class='hs-varid'>string</span> <span class='hs-varid'>expr</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>unsafePerformIO</span> <span class='hs-varop'>$</span> <span class='hs-keyword'>do</span>
<a name="line-61"></a> <span class='hs-varid'>putTraceMsg</span> <span class='hs-varid'>string</span>
<a name="line-62"></a> <span class='hs-varid'>return</span> <span class='hs-varid'>expr</span>
<a name="line-63"></a>
<a name="line-64"></a><a name="traceShow"></a><span class='hs-comment'>{-|
<a name="line-65"></a>Like 'trace', but uses 'show' on the argument to convert it to a 'String'.
<a name="line-66"></a>
<a name="line-67"></a>> traceShow = trace . show
<a name="line-68"></a>-}</span>
<a name="line-69"></a><span class='hs-definition'>traceShow</span> <span class='hs-keyglyph'>::</span> <span class='hs-layout'>(</span><span class='hs-conid'>Show</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>b</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>b</span>
<a name="line-70"></a><span class='hs-definition'>traceShow</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>trace</span> <span class='hs-varop'>.</span> <span class='hs-varid'>show</span>
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