Types that Change: The Extensible Type Design Pattern
summary
Defines an extensible type design pattern: an ADT parameterized by a type-function applied to every field so instantiations can be identity, Either String for parse errors, type+location annotations, Maybe for diffs, etc. Uses type-compose and cites Barbies; applies the pattern to Copilot and rewrites Ogma at NASA, cutting three separate AST representations down to one and removing large duplication; reports real-world validation with good results but notes harder pattern-matching and reliance on IDE/type-tooling.
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chapters (10)
- 0:00Extensible type design pattern
- 5:36Core concept
- 9:08Practical applications in compilers
- 14:26Embedding variables and expressions
- 17:22NASA with Copilot use case
- 22:24Beyond compilers
- 26:16Limitations and alternatives
- 30:12Tooling and IDE support
- 33:23Related work
- 36:10Closing remarks & Q&A
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