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Boxed: bringing algebraic types to TypeScript
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Matthias Le Brun
March 27, 2024
Technology
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Boxed: bringing algebraic types to TypeScript
Matthias Le Brun
March 27, 2024
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Transcript
Boxed
Matthias Le Brun @bloodyowl lead engineering manager chief shitpost office
the easiest way to provide banking features (accounts, payments, cards…) we're hiring! @
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PREVIOUSLY ON Matthias tries to convert people to FP
Algebraic Data Types yay
type State = { data?: Data; error?: Error; };
type State = { data?: Data; error?: Error; }; type
Result<Data> = | Ok<Data> | Error<Error>; error data ERROR NULL NULL DATA NULL NULL ERROR DATA
{ data: null; error: null; };
type Result<Data> = | Ok<Data> | Error<Error>;
type State = { data?: Data; error?: Error; }; type
Result<Data> = | Ok<Data> | Error<Error>; state ERROR DATA
API response API response
API response API response
type State = { data?: Data; error?: Error; }; type
Result<Data> = | Ok<Data> | Error<Error>; 2 2 1 1 4 2 x = + =
Algebra it's just basic math™
+ x
quiz 157 x 8341 = ?
quiz 999 + 1 = ?
union types
monads functors
functor
monad
[1, 2, 3].map(x => x * 2) // [2, 4,
6] [1, 2, 3].flatMap(x => [x, x * 2]) // [1, 2, 2, 4, 3, 6]
map: <A, B>(T<A>, (a: A) => B) => T<B>: flatMap:
<A, B>(T<A>, (a: A) => T<B>) => T<B>;
None
null & undefined are bad
errors aren't always exceptions
promises were made the wrong way in JS
promises were made the wrong way in JS
promises were made the wrong way in JS
promises were made the wrong way in JS
THAT WAS Matthias tries to convert people to FP NOW
LET'S TALK ABOUT BOXED
✨ new job ✨ 2022
«we use TypeScript»
None
let's look at the ecosystem™
fp-ts
pipe( token, TaskEither.bindW("user", getTokenFromUser), TaskEither.bindW("project", getProject), TaskEither.chainW(getMembership), ) no autocomplete
on current value
pipe( token, TaskEither.bindW("user", getTokenFromUser), TaskEither.bindW("project", getProject), TaskEither.chainW(getMembership), x => {}
) need to inspect argument for type
pipe( token, TaskEither.bindW("user", getTokenFromUser), TaskEither.bindW("project", getProject), TaskEither.chainW(getMembership), x => {}
) need to inspect argument for type not a good DX
export declare const chainFirstTaskK: <A, B>(f: (a: A) = >
T.Task<B>) = > <E>(first: TaskEither<E, A>) = > TaskEither<E, A> ah just what I was looking for
we've looked at the ecosystem™
«let's try to make these types work with a good
DX in a structurally typed language» — me, allegedly drunk
structural typing
class Some<A> {} class None {} const value: Some<string> =
new None();
what we need → good DX → interop with ts-pattern
→ fast
what we needed → chaining API → autocomplete → less
imports
1st iteration: naive wanted the types to be opaque but
safe
1st iteration: naive discriminator in TS (aka poor man's nominal
types)
1st iteration: naive and we're storing the state in the
class instance
None
1st iteration: naive wanted the types to be opaque but
safe
1st iteration: naive wanted the types to be opaque but
safe
2nd iteration: anger
2nd iteration: anger
2nd iteration: anger
2nd iteration: anger
3rd iteration: make it fast
initial release
initial release
type Option<A> = Some<A> | None;
type Result<A, E> = Ok<A> | Error<E>;
type AsyncData<A> = | NotAsked | Loading | Done<A>;
Future<A>; better promises™ cancellable monadic leaves error state to Result
const parsed = input != null ? parseInput(input) : undefined;
const transformed = parsed != null ? transform(parsed) : undefined; const printed = transformed != null ? print(transformed) : undefined; const value = printed != null ? prettify(printed) : "fallback"; input .map(parseInput) .flatMap(transform) .map(print) .map(prettify) .getWithDefault("fallback");
user-testing
None
insights people need human-written docs → we doubled down on
examples & added search
insights don't try to replicate another language → give good
defaults for TS
Result< Data, ServerError > Result< A, ServerError | FinalizeError >
insights people are familiar with just a few data types
→ reduce confusion
insights people can be docs-first or type-first → experience needs
to be good for both
insights readability matters → chaining API was the way to
go
insights mapping on existing JS knowledge helps → if it
exists, name it the same way
insights pipe() syntax had impact on the runtime → expressiveness
is important
4th iteration implement the feedback rename some methods update some
defaults
5th iteration: what the actual fu
5th iteration: what the actual fu
recently fix the errors
recently improved perf by 2x to 10x
recently improved perf by 2x to 10x blazing fast certi
fi ed™ ⚡
Boxed → github.com/swan-io/boxed → swan-io.github.io/boxed
None
$ yarn add @swan-io/boxed
Matthias Le Brun @bloodyowl we're still hiring thank you! 🙏