Make the code compile

* src/eval.ml (_eval): Eval body with the extra vars bound from the
pattern match.

* src/main.ml (default_grammar, default_stt): Remove; use Grammar instead.

* tests/REPL.ml (ipexp_parse): Reduce duplication.  Fix `nod' ref.
(ilexp_parse): Get it to type-check.
(ilexp_parse_all.loop, ieval_all.loop): Fix use of ::.
(ieval): Get it to type-check.
(repl.loop.print_e): Fix arg names.