* src/lparse.ml (_lexp_p_check): Check inferred type with conv_p

* btl/types.typer (head): Make it total.
(tail): Fix up minor type error.

* src/lexp.ml (lexp_unparse): Print `Sort` with more details.

* src/lparse.ml (_lexp_p_check): Check inferred type with conv_p.

* tests/eval_test.ml (Lists): Adjust to new `head` type.
(Monads): Fix type arguments.