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Debug.Trace

Portability | portable
Stability | provisional
Maintainer | libraries@haskell.org

Contents

Tracing

Description
The `trace` function.
Synopsis

putTraceMsg :: String -> IO ()
trace :: String -> a -> a
traceShow :: Show a => a -> b -> b

Tracing

putTraceMsg :: String -> IO () | Source

`putTraceMsg` function outputs the trace message from IO monad. Usually the output stream is System.IO.stderr but if the function is called from Windows GUI application then the output will be directed to the Windows debug console.

trace :: String -> a -> a | Source

When called, `trace` outputs the string in its first argument, before returning the second argument as its result. The `trace` function is not referentially transparent, and should only be used for debugging, or for monitoring execution. Some implementations of `trace` may decorate the string that's output to indicate that you're tracing. The function is implemented on top of `putTraceMsg`.

traceShow :: Show a => a -> b -> b | Source

Like `trace`, but uses `show` on the argument to convert it to a `String`.

     traceShow = trace . show

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