A comprehensive introduction to Higher Kinded Types in TypeScript, exploring how to encode and utilize these powerful abstractions from functional programming. HKTs enable type constructors that take other type constructors as arguments - imagine Functor<F> that works for any F<T> whether it’s Array<T>, Promise<T>, or Option<T>. Through encoding techniques using interface augmentation and symbol keys, we can simulate HKTs in TypeScript, making possible advanced functional patterns like monadic composition and type-safe algebraic structures previously impossible in the language.

Building composable type guard systems in TypeScript where runtime validation seamlessly integrates with compile-time type narrowing. Type guards like isString(x): x is string enable safe runtime checks, but composing them requires careful design. This explores combinators for union guards or(isNumber, isString): x is number | string, intersection guards and(hasName, hasAge): x is Person, and variadic patterns that preserve type inference. The result: elegant runtime validation that TypeScript’s control flow fully understands.

How many lambda calculus programs exist with exactly $N$ terms? This exploration dives into deep questions about computational complexity, from counting programs like (λx. x x) (λx. x x) to analyzing the non-computable BB(N) busy beaver function that grows faster than any computable sequence. We examine Chaitin’s constant $Ω$ and why determining program convergence connects to unsolved problems like the Collatz conjecture collatz(3n + 1).

Using TypeScript’s asserts syntax to create imperative-style type mutations, moving beyond method chaining to more familiar iterative patterns for complex type operations.

Solving the classic string deduplication algorithm entirely within TypeScript’s type system using literal string types and recursive type manipulation.

TypeScript 4.1’s variadic tuple types enable building complex type-safe data structures through method chaining, where each operation expands the chain’s type signature at compile time.

Exploring how to enforce type constraints across function maps in TypeScript, where every function must accept a specific parameter type.

TypeScript’s type predicates can modify the type of this itself, enabling self-modifying type behavior that approaches dependent types. By implementing is<K extends keyof ShapeTypes>(type: K): this is ShapeTypes[K] on abstract classes, we achieve compile-time type narrowing where shape.is('circle') transforms the shape variable’s type from Shape to Circle, unlocking properties like shape.radius within conditional blocks.

A functional TypeScript implementation of Dijkstra’s classic algorithm for parsing mathematical expressions, converting infix notation to reverse Polish notation for stack-based evaluation.

Attending the annual Slate Star Codex meetup in San Francisco’s Dolores Park, connecting with the rationalist community during my first summer in the Bay Area.