Data

Backup the state of the cache

All the shared data structures must be immutable.

Prepare for checking next class

1. Reset changed flag.

2. Commit current cache to stable cache if not changed.

3. Update stable heap if not changed.

4. Reset last cache.

Prepare cache for the next iteration

1. Reset changed flag.

2. Use current cache as last cache and set current cache to be empty.

3. Revert heap to stable.

Restore state from a backup

Evaluate an expression with cache

The algorithmic skeleton is as follows:

if don't cache result then
  return eval(expr)
if this.current.contains(config, expr) then
  return cached value
else
  val assumed = this.last(config, expr) or bottom value if absent
  this.current(config, expr) = assumed
  val actual = eval(expr)

  if assumed != actual then
    this.changed = true
    this.current(config, expr) = actual