Debugging in tkEdit

When a result is wrong and you do not know where, stop the program and look. tkEdit, the editor that comes with tiko, has a debugger: set a breakpoint, run to it, and read every variable while the program waits.

'' A program to stop inside: in tkEdit, F9 on the "total +=" line, then F6.
type Score
    player as ustring
    points as int32
end type

function Average( scores( ) as Score ) as float64
    dim total as int32
    for i as int32 = lbound( scores ) to ubound( scores )
        total += scores( i ).points
    next
    return total / ( ubound( scores ) - lbound( scores ) + 1 )
end function

dim scores( 1 to 3 ) as Score
scores( 1 ).player = "Ana"  : scores( 1 ).points = 12
scores( 2 ).player = "Bo"   : scores( 2 ).points = 15
scores( 3 ).player = "Cyd"  : scores( 3 ).points = 21
print "average:"; Average( scores( ) )

Output

average: 16

Open the file in tkEdit, put the cursor on line 10 (total += …) and press F9: a red circle in the margin marks the breakpoint. Press F6. tkEdit builds the program with -g -exx and without -O, runs it in its terminal, and stops on line 10 inside Average, with a yellow arrow in the margin. The output pane opens on its Debug tab, and the Locals tab shows:

• scores opens to scores(1), scores(2) and scores(3): elements are named by the subscripts the program uses, so they match the source. Each element opens to player and points, and a ustring shows its text, u"Ana". An array with more than a hundred elements opens to groups of them first.
• The Type column uses the debugger's names for the numeric types: an int32 is a long and a float64 a double.
• F10 runs line 10 and stops on the next one; press it again and again to watch total grow and i count. A value that changed since the last stop is shown in red.
• F6 continues to the next breakpoint — here, line 10 again, for the next element. Take the breakpoint away with F9 first, and Shift+F11 runs to the end of Average and stops back in the main program.

The keys:

On macOS each Ctrl is Cmd. All of them are on the Debug menu too.

Watch takes a name the way the program writes it: add a row with the + button, type scores(2).player, and press Enter. Case does not matter, and the subscript is the program's. A watch is a variable, a field or an element, not a calculation, and a name the stopped procedure cannot see shows <not in scope>.

Call Stack lists Average and, below it, main, the main program; a click on a frame shows that frame's locals and goes to its line. Breakpoints lists them all, and the buttons at the end of its tab row remove the selected one, or every one. Resting the mouse on a name in the source shows its value.

Activities

1. Step through the loop with F10 and stop when total is 27. What is i?
2. Add a watch on total / 3 and on total. Which one shows a value, and why?
3. Set a second breakpoint on the print line, remove the first one on the Breakpoints tab, and press F6 again.