Module Local_store

This module provides some facilities for creating references (and hash tables) which can easily be snapshoted and restored to an arbitrary version.

It is used throughout the frontend (read: typechecker), to register all (well, hopefully) the global state. Thus making it easy for tools like Merlin to go back and forth typechecking different files.

Creators

val s_ref : 'a -> 'a ref

Similar to Stdlib.ref, except the allocated reference is registered into the store.

val s_table : ('a -> 'b) -> 'a -> 'b ref

Used to register hash tables. Those also need to be placed into refs to be easily swapped out, but one can't just "snapshot" the initial value to create fresh instances, so instead an initializer is required.

Use it like this:

let my_table = s_table Hashtbl.create 42

State management

Note: all the following functions are currently unused inside the compiler codebase. Merlin is their only user at the moment.

type store
val fresh : unit -> store

Returns a fresh instance of the store.

The first time this function is called, it snapshots the value of all the registered references, later calls to fresh will return instances initialized to those values.

val with_store : store -> (unit -> 'a) -> 'a

with_store s f resets all the registered references to the value they have in s for the run of f. If f updates any of the registered refs, s is updated to remember those changes.

val reset : unit -> unit

Resets all the references to the initial snapshot (i.e. to the same values that new instances start with).

val is_bound : unit -> bool

Returns true when a store is active (i.e. when called from the callback passed to with_store), false otherwise.