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(m4.info)Trace

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Tracing macro calls
===================

   It is possible to trace macro calls and expansions through the
builtins `traceon' and `traceoff':

     traceon(...)
     traceoff(...)

When called without any arguments, `traceon' and `traceoff' will turn
tracing on and off, respectively,  for all defined macros.  When called
with arguments, only the named macros are affected.

   The expansion of `traceon' and `traceoff' is void.

   Whenever a traced macro is called and the arguments have been
collected, the call is displayed.  If the expansion of the macro call
is not void, the expansion can be displayed after the call.  The output
is printed directly on the standard error output.

     define(`foo', `Hello World.')
     =>
     define(`echo', `$@')
     =>
     traceon(`foo', `echo')
     =>
     foo
     error-->m4trace: -1- foo -> `Hello World.'
     =>Hello World.
     echo(gnus, and gnats)
     error-->m4trace: -1- echo(`gnus', `and gnats') -> ``gnus',`and gnats''
     =>gnus,and gnats

   The number between dashes is the depth of the expansion.  It is one
most of the time, signifying an expansion at the outermost level, but it
increases when macro arguments contain unquoted macro calls.

   Note: Debug Levels for information on controlling the details of
the display.