2f1bfd284c
Previously we tried to do the whole template parse in one pass. This was adequate for dealing with literals and interpolations because they create a flat structure, but to parse the template control sequences we need to be able to deal with nested template sequences. As a building block towards this, we first do a pass of extracting the template-level "tokens": literals, interpolations, control sequences. We then pass over that sequence of tokens and parse it, which is then simplified because the larger template atoms have already been produced.