Single-assignment variables

[sminnee]

Although mutable variables are something I'd like to stay away from initially, single-assignment variables should be supported, to do stuff like this:

main {
   x = [1,4,9,5];
   for(i in x) {
     printf("x[%i] = %i", i, x[i]);
   }
}

Once compiled, the printf should probably still refer directly to a const array.