Front end (part 4)

Recall, we left a number of unfinished  ... things in our parser.

word:
  [ [ w = WORD -> ...
    | "$"; "^" -> ...
    | "$"; "<" -> ...
    | "$"; "@" -> ...
    | "$"; "("; w = WORD; ")" -> ... ]
  ];

We now fill these in with Ocaml quasiquotations.
They come from our Ocaml model of Makefile semantics.
Aren't you glad we worked that out in advance?

word:
  [ [ w = WORD -> <:expr< [$str:w$] >> 
    | "$"; "^" -> <:expr< dep_names >>
    | "$"; "<" -> <:expr< [List.hd dep_names] >>
    | "$"; "@" -> <:expr< [targ] >>
    | "$"; "("; w = WORD; ")" -> let w2 = tidy w in 
                                 <:expr< ($lid:w2$ ()) >> ]
  ];