Error Messages in Type-Level DSLs
Surface helpful compile errors to DSL users.
Helpful Errors in Type-Level DSLs
The hardest part of a type-level DSL is making failures readable. Raw never or "not assignable" errors confuse users. We surface descriptive errors using branded error types and crafted never messages.
The Problem With never
When validation fails by resolving to never, the compiler says "Argument of type X is not assignable to never", which does not tell the user why. We can do better.
All lessons in this course
- What Is a Type-Level DSL
- Designing a Fluent Query DSL
- Compile-Time Input Validation
- Error Messages in Type-Level DSLs