We present a novel programming language design that attempts to combine the clarity and safety of high-level functional languages with the efficiency and parallelism of low-level numerical languages. We treat arrays as eagerly-memoized functions on typed index sets, allowing abstract function manipulations, such as currying, to work on arrays. In contrast to composing primitive bulk-array operations, we argue for an explicit nested indexing style that mirrors application of functions to arguments. We also introduce a fine-grained typed effects system which affords concise and automatically-parallelized in-place updates. Specifically, an associative accumulation effect allows reverse-mode automatic differentiation of in-place updates in a way that preserves parallelism. Empirically, we benchmark against the Futhark array programming language, and demonstrate that aggressive inlining and type-driven compilation allows array programs to be written in an expressive, "pointful" style with little performance penalty.

@article{paperbot1137,
  title = {Getting to the point: index sets and parallelism-preserving autodiff for pointful array programming},
  author = {Adam Paszke and Daniel D. Johnson and David Duvenaud and Dimitrios Vytiniotis and Alexey Radul and Matthew J. Johnson and Jonathan Ragan-Kelley and Dougal Maclaurin},
  journal = {Proceedings of the ACM on Programming Languages},
  volume = {5},
  number = {ICFP},
  year = {2021},
  doi = {10.1145/3473593}
}