Module Local_store

module Local_store: sig .. end

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

let s_ref: 'a => ref('a);

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

let s_table: ('a => 'b, 'a) => ref('b);

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;

let 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.

let with_store: (store, unit => 'a) => 'a;

with_scope 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.

let reset: unit => unit;

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

let is_bound: unit => bool;

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