hmm ... why is a list L = [ a, b, c ] converted to a mapping { null: a, null: b, null: c } (which is invalid on its face, due to having a repeated key) instead of M = { 0: a, 1: b, 2: c } so that M[i] is L[i] for each index i; and M, L have the same set of valid indices ?  That's certainly what I'd want to do in JavaSpit, regardless of whatever we do with our slists - do they even *have* an indexing mechanism ? - given that JavaSpit really does think about lists like this.