(dune seems to choke on some 4.08 features that were used in the Env
codebase already. It's not a bad idea to ensure that the compiler
codebase works well with 4.07.)
The hope is that a tailor-made algebraic datatype is more readable /
less confusing than using ('a option) directly -- one may confuse
getting None when looking in a table with the Not_found case.
(Suggested by Jérémie Dimino)
Persistent_env is a new module that handles the relation between the
type-checking state and the "persistent" typing information laying in
.cmi files on the filesystem. In particular, it handles the collection
and production of CRC information for the .cmi files being read and
written to the filesystem; the using modules (in our case, only Env)
are in charge of turning the cmi files into higher-level information
(components and signatures).
Persistent_env exposes a type `'a t` of a persistent environment,
which acts as a mutable store of `'a` values. There is no global state
in the module itself: while Env (and thus the OCaml type-checker) uses
a single global persistent environment, it should be possible to
create several independent environments to represent, for example,
several independent type-checking sessions.
Leo White
Gabriel Scherer
Mark Shinwell