# Revision history for hegg

## Unreleased

## 0.6.0.0 -- 2024-07-13

* Fix a soundness bug that would cause equality saturation to be broken when
  `VariablePattern` was used explicitly with low numbers such as 1,2,3...
  This bug could also be triggered in the unlikely case when the hash of the
  given IsString variable instance collided with the Var Ids internally
  associated to NonVariablePatterns. Fixes #20 and #32.

## 0.5.0.0 -- 2023-10-31

* Change `'modifyA'` to instead operate over e-graphs, instead of being
    constrained to editing the e-class that prompted the modification.
    (Remember that the e-graph lenses in `'Data.Equality.Graph.Lens'` are the
    preferred way to edit the e-graph and the desired e-class (by id), and its
    data, etc...)

* Fix compilation of Data.Equality.Graph.Dot, the graphviz rendering backend
    (despite there being some usability bugs still) (by @BinderDavid)

* Dropped support for GHC 9.0 because of the QuantifiedConstraints bug (by @phadej)

* Add `AnalysisM`, a class for e-graph analysis that are only well-defined
    within a certain monadic context. Accordingly, we also add versions of the
    current e-graph transformation functions (such as `add` and `merge`) for
    analysis defined monadically (such as `addM` and `mergeM`).

* Add operation to create empty e-classes with explicit domain data
    (experimental, not sure whether this is something good to keep in the API)

## 0.4.0.0 -- 2023-06-24

* Make `Language` a constraint type synonym instead of a standalone empty class
* Use `QuantifiedConstraints` instead of `Eq1,Ord1,Show1` in the implementation,
    which results in the user only having to provide an `Eq a => Eq (language
    a)` instance rather than a `Eq1 language` one (which is much simpler and can
    usually be done automatically!)
* Make `_classes` a `Traversal` lens over all e-classes rather than a `Lens` into `IntMap EClass`

## 0.3.0.0 -- 2022-12-09

* A better `Analysis` tutorial in the README.

* Complete `Analysis` redesign.
    * The `Analysis` class now has two type parameters: a `domain` and a
        `language`, and no longer has an associated type family
    * The analysis no longer has any knowledge of the e-graph:
        * `makeA` now has type `l domain -> domain`, that is, to make a domain
            of a new node we only have to take into consideration the data of
            the sub-nodes of the new node.
        * `joinA` is unchanged.
        * `modifyA` now has type `EClass domain lang -> (EClass domain lang,
            [Fix lang])`. It takes an e-class and optionally modifies it,
            possibly by adding nodes to it. The return value is the modified
            e-class, and a list of expressions from the language to add to the
            e-class.
    * We can now compose analysis and create language-polymorphic analysis. Such
        two examples are the analysis with domain `()` which regardless of the
        language simply ignores the domain: `instance Analysis () l`; and the
        second example is the product of analysis, which composes two separate
        analysis into one: `instance (Analysis a l, Analysis b l) => Analysis
        (a,b) l`.
    * An `EGraph` now also has two type parameters instead of one (the latter is
      the language is the former the domain of the analysis).

* Allow customization of Schedulers through parameters (by accepting a scheduler
    rather than a proxy for it)

## 0.2.0.0 -- 2022-09-19

* Expose `runEqualitySaturation` to run equality saturation on existing e-graphs
    whole instead of focusing on individual expressions
* (Very) significant performance improvements!
* Make `CostFunction` polymorphic over the `Cost` type, requiring that type
    to instance `Ord`
* Make e-graph abstract. The internal structure can still be modified through
    the available lenses in `Data.Equality.Graph.Lens`
* Fix a bug related to `NodeMap`'s size.

## 0.1.0.0 -- 2022-08-25

* First version. Released on an unsuspecting world.