Debugging
Track program execution.
Debugging commands are essential to find programming errors. They help with inspecting programs and data, to pause a program, to find out why a program takes too much time, and much more. Logo can pause because of several reasons:
- The PAUSE command has been executed
- A runtime error has been hit
- The PAUSE icon has been clicked, or the F4 key has been pressed
The debugging icons in the Toolbar have the following meaning:
| Icon | Key | Command | Explanation |
|---|---|---|---|
 |
F3 | TOPLEVEL | Halts a program and returns to toplevel. |
 |
F4 | PAUSE | Pauses a program and enters Pause mode. |
BACKTRACE
Also: BT
Prints a backtrace.
Syntax
BACKTRACE
Description
The BACKTRACE command is only available during a PAUSE. It prints to the current chain of the active procedures, FOR and REPEAT loops, run lists etc. See also CONTINUE.
CONTINUE
Also: CO
Ends a pause.
Syntax
CONTINUE
Description
CONTINUE ends a pause. A Logo program can pause because is it is stepped
(see STEP), because a breakpoint has been hit, or the PAUSE
command has been executed, or if Logo has hit a runtime error.
NOTE: The abbreviation CO is usually an
abbreviation for the ALL command. Only during a pause,
CO is redefined to CONTINUE.
EXECTIME
Outputs the number of microseconds spent inside a procedure.
Syntax
EXECTIME
Description
EXECTIME outputs a timer value in microseconds. This timer is local to a procedure and starts once the procedure is invoked. EXECTIME is handy to measure execution times of a procedure.
Example
TO TESTTIMER PR EXECTIME WAIT 1234 PR EXECTIME END
TESTTIMER </span>
PAUSE
Pauses a procedure.
Syntax
PAUSE
Description
PAUSE temporarily halts the execution of a procedure. PAUSE makes it possible to check variables or change the environment during the execution of a procedure. Using the PAUSE command is equivalent to setting a breakpoint in the editor window. When Logo pauses, the editor windows are set to read-only, because the procedure environment is “frozen”. Command like TO or DEFINE are also disabled when Logo pauses. To resume execution of the procedure, press the GO button or type CO or CONTINUE. To return to toplevel, press the STOP button or type TOPLEVEL. PAUSE may only be used within a procedure.
Example
TO SQUAREDRAW FORWARD 60 RT 90 PAUSE REPEAT 3 [FD 60 RT 90] END
SQUAREDRAW </span>