Section Intro: Debugging Commands

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Section Intro: Debugging Commands

Debugging Commands

Synopsis:

Debugging a CGI application executing under a running Web server can be quite problematic. Meta-HTML provides the following functions, macros, and variables in an effort to alleviate the problems associated with this situation.

Commands:

%%stack-trace
debugging-on
debugging-output

dump-alist
dump-all-packages
dump-package

page-debug
system-error-output

More Information:

In addition to the functions and variables above, Meta-HTML has a complete source language debugger called mdb, which can be used to interactively execute expressions, to place breakpoints in files and then run them examining local and global variables, and to single-step through source code that you have written in Meta-HTML. Instructions on the use of the debugger is beyong the scope of this manual -- please see MDB: A User's Guide to Debugging Meta-HTML Programs for more information specific to the debugger.

<%%stack-trace Simple

Return an array of function calls that are pending the return of this one. This functionality can only be turned on by setting the variable mhtml::remember-function-calls to a non-empty value.

<debugging-on &optional [FUNCTION-NAME=LEVEL...] Simple

Turns on debugging for the FUNCTION-NAMEs mentioned, setting the level of output to LEVEL. LEVEL is a number between 0 (the least amount of debugging info) and 10 (the maximum amount of debugging info).

The output is placed into the Meta-HTML internal debugger buffer, and can be placed into an output page by simply placing the tag <DEBUGGING-OUTPUT> somewhere in the page, or can be explicity retrieved using <debugging-output retrieve>.

<debugging-output &optional [ACTION...] Simple

Meta-HTML stores debugging information in an internal buffer. You may directly place information into this buffer using the page-debug command, and you may retrieve or clear this buffer using <debugging-output>.

Possible values for ACTION are:

retrieve
Inserts the current contents of the debugging buffer into the page at the current location.
clear
Empties the debugging buffer of all stored information.

If you place <debugging-output> into your page without passing any arguments, Meta-HTML treats this invocation specially; it marks the location at which any debugging statements which have been collected during the processing of the entire page should be placed.

We recommend that you always place this tag somewhere in the output page, whenever that output is an HTML document, as opposed to a standalone script.

<dump-alist #ALIST &key [RECURSE?] Simple

Dump out the contents of ALIST in the same fashion as dump-package would.

<dump-all-packages &key [RECURSE?] Simple

Call dump-package on every defined package. If the keyword argument RECURSE? is supplied, it indicates that any association lists found as values in the package variables should be dumped out as well.

<dump-package &key [RECURSE?] [TEXT-MODE?] &rest packages[]> Simple

Dump the contents of the specified PACKAGES in a format suitable for including in HTML output. If the keyword argument RECURSE? is non-empty, then recursively dump the contents of any alists found as values in PACK. If the keyword argument TEXT-MODE? is non-empty, then dump the contents of the packages in a format suitable for placing within a <PRE> ... </PRE> construct. This happens automatically when running under mdb.

<page-debug &rest body> Simple

Cause BODY to be inserted into the debugger output.

<system-error-output &optional [ACTION...] Simple

Meta-HTML stores system error information in an internal buffer. Such information may be the results of an error which occurred during the execution of an external command (such as with cgi-exec), or other information which is generated by the inability of Meta-HTML to access a particular file (such as with the require command).

You may retrieve or clear this buffer using <system-error-output>.

Possible values for ACTION are:

retrieve
Inserts the current contents of the system error buffer into the page at the current location.
clear
Empties the system error buffer of all stored information.

If you place <system-error-output> into your page without passing any arguments, Meta-HTML treats this invocation specially; it marks the location at which any system errors which have been collected during the processing of the entire page should be placed.

We recommend that you always place this tag somewhere in the output page, whenever that output is an HTML document, as opposed to a standalone script.

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