check out the placement of the moop in output

oo::class create Tuple {
    method f {f} {
	puts stderr "f $f"
	if {$f == 0} {
	    my n 1
	}
	info frame -1
	puts moop
    }

    method n {{n 0}} {
	puts stderr "n $n"
	my f $n
	#info frame -1
    }
}

[Tuple new] n

tclsh test.tcl
n 0
f 0
n 1
f 1
moop
Segmentation fault