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Need-finding (what are problems), formative (how to solve?), evaluative (did it work?)
Need-finding means asking users to show, don’t tell. Where do they get frustrated? Where do they give up?
- If you can only interview, have people talk concrete. “What was the most annoying part of this task?”
PLs can support many tasks
- Incrementally adding functionality, transpiling, modifying, exploring, searching through a codebase, exploring a codebase for understanding
Notation has a number of different cognitive dimensions
- See the notes for full deets
- Basically: is it easy to abstract? Is it easy to change things? What is made visible and comparable? Are the abstractions close to mental model? Are things consistent? Verbose? Mental load?
To design a language…
- Figure out what users need
  - Formative studies
  - Write out programs in domain and brainstorm abstractions
  - Learn how people talk about their task

Considerations from languages past

Lisp: Good News, Bad News, How to Win Big: simplicity and interop over theoretical perfection and monolithic systems. C sucks, but is easy to implement and works with lots of things. Easier to get fix C once adopted than make ivory tower perfect and try to get it adopted.
Hints on Programming Language Design: design for clarity and ease/speed of compilation. Allow lots of overloading (broadcasting, dot notation) to allow for changing for efficient internal repr. Think Julia.
Why Functional Programming Matters: higher-order functions and lazy programming lets us do modularization. infinite stream generation and taking!
Can programming be liberated from the von Neumann style?: APL-style is good! No individual memory location manipulation, more big operations: + on arrays, etc. Hard to parallelize, statements make it hard to deal with mathematically.
How enterprises use functional languages, and why they don’t: gripes with Haskell

Nested data parallelism was new! Think Rayon, with work-stealing thread pool.

Datalog is a database of facts and rules to deduce new facts.
Optimizations
- Semi-naïve: new-old, old-new, new-new
- Magic set: specialize functions for queries.
Stratified negation: separate execution into distinct phases to enable negation.
Lattices, semirings