Adding linear interpolation to an array

[Dave Whipp]

I was trying to work out how to get non-integer indexes working for an 
array -- initially using linear interpolation, though perhaps later it 
would be generalized. Can anyone comment on whether this simple role 
would work as I expect. Does defining the invocant as "Num @self is 
constant" constrain the application of the role to read-only uses of 
indices? Does the explicit indexing by an "int" typed value ensure that 
it'll be non-recursive under MMD?

  role LinearInterpolation
  {
    multi method Num postcircumfix:«[]» (
        Num @self is constant : Num $real_index)
    {
       int $integer_index = int $real_index;
       Num $first_value = @self[$integer_index];
       return $first_value if $integer_index == $real_index;
       Num $second_value = @self[$integer_index+1];
       Num $delta = $second_value - $first_value;
       Num $weight = $real_index - $integer_index;
       return $first_value + $delta * $weight;
    }
  }
  my @test does LinearInterpolation;
  @test[0] = 1;
  @test[1] = 3;
  assert @test[0] == 1;
  assert @test[0.5] == 2;
  assert @test[1] == 3;
If I later decare a sub as
  sub foo ( @in does LinearInterpolation ) { ... }
Would I be able to pass a normal (non-interpolating) array to this sub, 
and then access it using non-integer indices (i.e. is the data in the 
array independent of the interface through wich it is accessed).

Dave.