Exploring Expect

Stepping Over Procedure Calls

The n command executes the pending command—in this case "set b 1“—and displays the next command to be executed.

dbg2.2> n
1: proc p4 {x} {
    return [
        expr 5+[expr 1+$x]]
}
dbg2.3> info exists b
1

The command "info exists b" confirms that b has been set. The procedure p4 is about to be defined.

dbg2.4> n
4: p4 $b
dbg5.5>

The procedure p4 has now been defined. The next command to be executed is p4 itself. It appears in the command:

set z [
    expr 1+[expr 2+[p4 $b]]
]

The three sets of braces introduce three new levels on the evaluation stack; hence the stack level in which p4 is about to be executed is shown as 4.^[63]

Notice that the evaluation stack level does not affect the scope. I am still in the top-level scope and b is still visible.

dbg5.5> info exists b
1

The argument to p4 is $b. The value of this variable can be evaluated by using set or puts.

dbg5.6> set b
1
dbg5.7> puts $b
1

Another n command executes p4, popping the stack one level. Additional n commands continue evaluation of the "set z" command, each time popping the stack one level. It is not necessary to enter "n" each time. Pressing return is sufficient. Expect remembers that the last action command was an n and executes that.

dbg5.8> n
3: expr 2+[p4 $b]
dbg4.9>
2: expr 1+[expr 2+[p4 $b]]
dbg3.10>
1: set z [
    expr 1+[expr 2+[p4 $b]]
]
dbg2.11>

It is often useful to skip over multiple commands embedded in a single complex command and just stop the debugger before it executes the last command. The N