Your first call to foo is not a function call because foo() is not defined at that point.

Try this (slightly cleaned up code):

my $e = 'my $i=0;
      sub foo{
        print "$i foo\n";
        if ($i < 10){
          $i++;
          print "calling foo\n";
          foo();
        }
      }
      foo;';
eval "$e";
print $@,"\n";
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Use strict would have told you this.

Joost.