How can I keep these values local to my function?

I want to be able to specify binary combinations of options the way that, e.g., vecsort() does. I couldn't see a way to do that so I created a function, makeoptions(), that returns a vector in the form ["a=1","b=2",...] and I use eval() on that vector to create those variables within my function. My problem is that eval() creates them with global scope, and I can't see a way to make them local.

/* Takes a string containing a list of option names and a number whose binary digits represents those options. Returns variables set accordingly. */
makeoptions(s="",options=0)=
{
    if(s=="",return());
    my(v=strsplit(s," "));
    return(vector(#v,i,(Str(v[i],"=",bitand(2^(i-1),options)<>0))))
}
/* A function that uses makeoptions() */
f(n)={
    my(a=eval(makeoptions("One Two Three", n)));
    my(b=eval(makeoptions("Four Five Six", n+1)));
    print("a=",One,Two,Three);
    print("b=",Four,Five,Six);
    }

Here's the output from my function:

(10:31) > f(2)
a=010
b=110
(10:31) > One \\ Should be undefined
%2 = 0
(10:32) > Four \\ Should be undefined
%3 = 1

Is there a way to make these variables local, or another way to achieve what I want: local named variables set at run time without having a routine along the lines of Opt1=bitand(options,1); Opt2=bitand(options,2); ...

Thanks,

Joe Slater