debugging with expect

When I try to debug with expect, the following can be seen:

pme $ expect -D 1 f.tcl
1: binary format "f*" 1.1 2.1 3.1
dbg1.0> pme $

1. evaluation stack is 1 (dbg1.0) instead of 2
2. the expect quits and the shell prompt returns

How can I use expect to debug tcl scripts?

Using expect version 5.42.1

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