diff options
| -rw-r--r-- | libraries/base/Debug/Trace.hs | 10 |
1 files changed, 5 insertions, 5 deletions
diff --git a/libraries/base/Debug/Trace.hs b/libraries/base/Debug/Trace.hs index c81abbf653..47abcaeda8 100644 --- a/libraries/base/Debug/Trace.hs +++ b/libraries/base/Debug/Trace.hs @@ -60,7 +60,11 @@ import Data.List -- The 'trace', 'traceShow' and 'traceIO' functions print messages to an output -- stream. They are intended for \"printf debugging\", that is: tracing the flow -- of execution and printing interesting values. - +-- +-- All these functions evaluate the message completely before printing +-- it; so if the message is not fully defined, none of it will be +-- printed. +-- -- The usual output stream is 'System.IO.stderr'. For Windows GUI applications -- (that have no stderr) the output is directed to the Windows debug console. -- Some implementations of these functions may decorate the string that\'s @@ -102,10 +106,6 @@ For example, this returns the value of @f x@ but first outputs the message. > trace ("calling f with x = " ++ show x) (f x) -The 'trace' function evaluates the message (i.e. the first argument) completely -before printing it; so if the message is not fully defined, none of it -will be printed. - The 'trace' function should /only/ be used for debugging, or for monitoring execution. The function is not referentially transparent: its type indicates that it is a pure function but it has the side effect of outputting the |