my $str = join '', map{s/\s+//g;$_}<DATA>;
while($str =~ /@(\w+){([^}]*)}/g){
    my ($int, $imp) = ($1,$2);
    print "<$int>\n";
    printf qq{\t<%s name="%s" width="%s"/>\n}, $2,$1,$3
        while $imp=~/([^:]+):([^(]+)\((\d+)\);/g;
    print "</$int>\n";
}
__DATA__
@interface {
    i : in(1);
    o : out(1);
}
@interface2 {
    b : out(1);
    a : in(1);
}
@interface3 {
    x : in(1);
    y : in(1);
}
@interface4 {
    f : out(1);
    b : out(1);
}

OUTPUT:
<interface>
	<in name="i" width="1"/>
	<out name="o" width="1"/>
</interface>
<interface2>
	<out name="b" width="1"/>
	<in name="a" width="1"/>
</interface2>
<interface3>
	<in name="x" width="1"/>
	<in name="y" width="1"/>
</interface3>
<interface4>
	<out name="f" width="1"/>
	<out name="b" width="1"/>
</interface4>