Format of TRACE output

Every clause traced appears with automatic formatting (indentation) according to its logical depth of nesting and so forth. The language processor may replace any control codes in the encoding of data (for example, EBCDIC values less than '40'x) with a question mark (?) to avoid console interference. Results (if requested) are indented an extra two spaces and are enclosed in double quotation marks so that leading and trailing blanks are apparent.

A line number precedes the first clause traced on any line. If the line number is greater than 99999, the language processor truncates it on the left, and the ? prefix indicates the truncation. For example, the line number 100354 appears as ?00354. All lines displayed during tracing have a three-character prefix to identify the type of data being traced. These can be:

*-*: Identifies the source of a single clause, that is, the data actually in the program.
+++: Identifies a trace message. This may be the nonzero return code from a command, the prompt message when interactive debug is entered, an indication of a syntax error when in interactive debug, or the traceback clauses after a syntax error in the program (see below).
>>>: Identifies the result of an expression (for TRACE R) or the value assigned to a variable during parsing, or the value returned from a subroutine call.
>.>: Identifies the value "assigned" to a placeholder during parsing (see The period as a placeholder).

The following prefixes are used only if TRACE Intermediates is in effect:

>C>: The data traced is the name of a compound variable, traced after substitution and before use, provided that the name had the value of a variable substituted into it.
>F>: The data traced is the result of a function call.
>L>: The data traced is a literal (string, uninitialized variable, or constant symbol).
>O>: The data traced is the result of an operation on two terms.
>P>: The data traced is the result of a prefix operation.
>V>: The data traced is the contents of a variable.

If no option is specified on a TRACE instruction, or if the result of evaluating the expression is null, the default tracing actions are restored. The defaults are TRACE N, command inhibition (!) off, and interactive debug (?) off.

Following a syntax error that SIGNAL ON SYNTAX does not trap, the clause in error is always traced. Any CALL or INTERPRET or function invocations active at the time of the error are also traced. If an attempt to transfer control to a label that could not be found caused the error, that label is also traced. The special trace prefix +++ identifies these traceback lines.