Debugging And Error Handling

(trace <sym>)  ADD A FUNCTION TO THE TRACE LIST
    <sym>       the function to add (quoted)
    returns     the trace list

(untrace <sym>)  REMOVE A FUNCTION FROM THE TRACE LIST
    <sym>       the function to remove (quoted)
    returns     the trace list

(error <emsg> [<arg>])  SIGNAL A NON-CORRECTABLE ERROR
    <emsg>      the error message string
    <arg>       the argument expression (printed after the message)
    returns     never returns

(cerror <cmsg> <emsg> [<arg>])  SIGNAL A CORRECTABLE ERROR
    <cmsg>      the continue message string
    <emsg>      the error message string
    <arg>       the argument expression (printed after the message)
    returns     nil when continued from the break loop

(break [<bmsg> [<arg>]])  ENTER A BREAK LOOP
    <bmsg>      the break message string (defaults to "**BREAK**")
    <arg>       the argument expression (printed after the message)
    returns     nil when continued from the break loop

(clean-up)  CLEAN-UP AFTER AN ERROR
    returns     never returns

(top-level)  CLEAN-UP AFTER AN ERROR AND RETURN TO THE TOP LEVEL
    returns     never returns

(continue)  CONTINUE FROM A CORRECTABLE ERROR
    returns     never returns

(errset <expr> [<pflag>])  TRAP ERRORS
    <expr>      the expression to execute
    <pflag>     flag to control printing of the error message
    returns     the value of the last expression consed with nil
                or nil on error

(baktrace [<n>])  PRINT N LEVELS OF TRACE BACK INFORMATION
    <n>         the number of levels (defaults to all levels)
    returns     nil

(evalhook <expr> <ehook> <ahook> [<env>])  EVALUATE WITH HOOKS
    <expr>      the expression to evaluate
    <ehook>     the value for *evalhook*
    <ahook>     the value for *applyhook*
    <env>       the environment (default is nil)
    returns     the result of evaluating the expression