Adapton in Rust

A general-purpose Incremental Computation (IC) library for Rust.

Based on:

• The paper Incremental Computation with Names, 2015.

• A prior OCaml implementation.

Development Activities

• The library exposes a small core interface.
  See the Adapton trait.

• The library implements this interface with an imperative data structure.
  See AdaptonState.
  See also: Incremental Computation with Names, 2015.

• Rust macros provide syntactic sugar.
  See adapton_syntax.

Testing:

• Lazy Evaluation (simple, pure caching).

• Function Caching:

  • Implements Bill Pugh's notion of IC, pure function caching.

• Structural Adapton:

  • changeable input cells
  • bidirectional DCG structure
  • dirtying traversal; repair traversal.

• Nominal Adapton:

  • first-class names
  • nominal memoization

• Incremental Data Structures and Algorithms.

  • generic list and tree traits
  • balanced trees from lists ("unfold")
  • tree folds (left-to-right, right-to-left, bottom-up)
  • mergesort

Future work

Data Structures and Algorithms

• tries that represent sets, maps,
• generic fixed-point loop
• graphs, graph exploration algorithms (e.g., search)

Technical Debt

Pending issues:

• Canonical balanced trees for sequences: Where should data go? Only at leaves (B-Tree style)?
• List/Tree intro forms should take unboxed, references, or boxes? error: type annotations required: cannot resolve <_ as structures::ListT<A, _>>::List == _ [E0284]
• Implement ArtId::Structural for cell and thunk to do hashing internally, not externally.

Rust Q&A

• http://users.rust-lang.org/t/trait-objects-with-associated-types/746/16?u=matthewhammer

• The concept of "object safety" seems to bite me a lot in naive designs:

src/adapton_impl.rs:653:51: 653:111 error: cannot convert to a trait object because trait `adapton_impl::Producer` is not object-safe [E0038]
...
src/adapton_impl.rs:653:51: 653:111 note: method `eq` references the `Self` type in its arguments or return type

I sidestepped this problem in adapton_state.rs twice: by writing Producer::copy and the ShapeShifter trait. Both avoid returning a Self.

• Do I need really need Rc<Box<Fn (_) -> _>> instead of Rc<Fn (_) -> _>? (Why?)