Control the generation of BOS/EOS callback code
Int_Type _boseos_info
This value of this variable dictates whether or not the S-Lang interpeter will generate code to call the beginning and end of statement callback handlers. The value of this variable is local to the compilation unit, but is inherited by other units loaded by the current unit.
The value of _boseos_info controls the generation of code for
callbacks as follows:
Value Description
-----------------------------------------------------------------
0 No code for making callbacks will be produced.
1 Callback generation will take place for all non-branching
statements.
2 Same as for 1 with the addition that code will also be
generated for branching statements.
break, continue, and return.
Consider the following:
_boseos_info = 1;
define foo ()
{
if (some_expression)
some_statement;
}
_boseos_info = 2;
define bar ()
{
if (some_expression)
some_statement;
}
foo will be compiled with code generated to call the
BOS and EOS handlers when some_statement is executed. The
function bar will be compiled with code to call the handlers
for both some_expression and some_statement.
The sldb debugger and slsh's stkcheck.sl make use of this
facility.
_set_bos_handler, _set_eos_handler, _debug_info
Clear an error condition (deprecated)
_clear_error ()
This function has been deprecated. New code should make use of try-catch exception handling.
This function may be used in error-blocks to clear the error that triggered execution of the error block. Execution resumes following the statement, in the scope of the error-block, that triggered the error.
Consider the following wrapper around the putenv function:
define try_putenv (name, value)
{
variable status;
ERROR_BLOCK
{
_clear_error ();
status = -1;
}
status = 0;
putenv (sprintf ("%s=%s", name, value);
return status;
}
putenv fails, it generates an error condition, which the
try_putenv function catches and clears. Thus try_putenv
is a function that returns -1 upon failure and 0 upon
success.
_trace_function, _slangtrace, _traceback
Configure debugging information
Integer_Type _debug_info
The _debug_info variable controls whether or not extra code
should be generated for additional debugging and traceback
information. Currently, if _debug_info is zero, no extra code
will be generated; otherwise extra code will be inserted into the
compiled bytecode for additional debugging data.
The value of this variable is local to each compilation unit and setting its value in one unit has no effect upon its value in other units.
_debug_info = 1; % Enable debugging information
Setting this variable to a non-zero value may slow down the interpreter somewhat.
The value of this variable is not currently used.
_traceback, _slangtrace
Set the beginning of statement callback handler
_set_bos_handler (Ref_Type func)
This function is used to set the function to be called prior to the beginning of a statement. The function will be passed two parameters: the name of the file and the line number of the statement to be executed. It should return nothing.
static define bos_handler (file, line)
{
() = fputs ("About to execute $file:$line\n"$, stdout);
}
_set_bos_handler (&bos_handler);
The beginning and end of statement handlers will be called for
statements in a file only if that file was compiled with the variable
_boseos_info set to a non-zero value.
_set_eos_handler, _boseos_info
Set the beginning of statement callback handler
_set_eos_handler (Ref_Type func)
This function is used to set the function to be called at the end of a statement. The function will be passed no parameters and it should return nothing.
static define eos_handler ()
{
() = fputs ("Done executing the statement\n", stdout);
}
_set_eos_handler (&bos_handler);
The beginning and end of statement handlers will be called for
statements in a file only if that file was compiled with the variable
_boseos_info set to a non-zero value.
_set_eos_handler, _boseos_info
Turn function tracing on or off
Integer_Type _slangtrace
The _slangtrace variable is a debugging aid that when set to a
non-zero value enables tracing when function declared by
_trace_function is entered. If the value is greater than
zero, both intrinsic and user defined functions will get traced.
However, if set to a value less than zero, intrinsic functions will
not get traced.
_trace_function, _traceback, _print_stack
Generate a traceback upon error
Integer_Type _traceback
_traceback is an intrinsic integer variable whose value
controls whether or not a traceback of the call stack is to be
generated upon error. If _traceback is greater than zero, a
full traceback will be generated, which includes the values of local
variables. If the value is less than zero, a traceback will be
generated without local variable information, and if
_traceback is zero the traceback will not be generated.
Running slsh with the -g option causes this variable to be
set to 1.
_boseos_info
Set the function to trace
_trace_function (String_Type f)
_trace_function declares that the S-Lang function with name
f is to be traced when it is called. Calling
_trace_function does not in itself turn tracing on. Tracing
is turned on only when the variable _slangtrace is non-zero.
_slangtrace, _traceback