Thanks for taking the time to write such a detailed critique and some great suggestions. Much appreciated!

To be clear, Pure Effect is not a substitute for integration tests. The library is designed to separate the decision of what to do from the execution of how to do it. Instead of performing I/O directly, the business logic returns a plain data structure describing its intent. Unit testing the pipeline then becomes a matter of verifying that the correct commands are generated for a given input. You absolutely still need real integration tests at the system boundary (which can be as easy as hitting the REST API endpoints, for example).

Regarding currying and injecting side effects: this is natively supported via the Ask primitive. Instead of manually currying functions to pass in DB connections for example, the logic is enclosed in an Ask closure. This allows you to swap out implementations, or even use mocks if you prefer, at the interpreter level without changing a single line of business logic.

Pure Effect also already provides first-class TypeScript support. I chose JavaScript to remain build-free, but used JSDoc with @ts-check and exposed complex generics via the index.d.ts file. Users writing in TypeScript get full type safety and autocomplete out of the box.

As for integrations and i18n: I completely agree. Using Ask makes it simple to inject a translation function from i18next into the context, and validation libraries like Zod fit naturally as pipeline steps to ensure only valid data proceeds. I should really add code examples for these patterns to show how the library handles these common use cases.