Visual FreePro offers a new debugging tool called breadcrumbs. It leaves a trail back through source code indicating what lines were traversed at runtime. It can be set manually in the debugger, or through VXB++ (xbase) commands.

The debugger offers features to step forward/backward through source code on the breadcrumbs trail. In addition, an optional DELTAS feature lets you see what was changed on every source code line, and to step forward and backward through deltas, including also searching for those lines which affected a certain memory variable, table, row, anything that was changed on each line.

Breadcrumbs can be set to signal on a line-by-line basis, or signal horizontally showing the deltas across each sub-expression and in-flight parameter. Using deltas slows down processing somewhat, but using the regular breadcrumb trail has almost no impact on runtime performance.

This example sets the breadcrumb trail history to 5. However, it can be set to any value, including just setting it to ON so it will record forever.

See:
http://www.visual-freepro.org/wiki/index.php/VXB%2B%2B#SET_BREADCRUMBS_ON.7COFF.7CTO_nCount_.5BDELTAS.5D_.5BHORIZONTAL.5D_.5BADDITIVE.5D

If that link doesn't work, try this, and search for "SET BREADCRUMBS" on the page:
http://www.visual-freepro.org/wiki/index.php/VXB%2B%2B

You can also explicitly look at the animated GIF example here:
http://www.visual-freepro.org/wiki/index.php/File:Breadcrumbs.gif