Principle:Helicone Helicone Result Type Pattern
| Knowledge Sources | |
|---|---|
| Domains | Error Handling, Type Safety, Functional Programming |
| Last Updated | 2026-02-14 06:32 GMT |
Overview
The Result Type Pattern encodes operation outcomes as discriminated unions that force callers to explicitly handle both success and failure cases at compile time.
Description
Traditional error handling with exceptions or null returns makes it easy to forget error cases, leading to uncaught runtime failures. The Result type pattern replaces this with a discriminated union (also called a tagged union) that is either a success variant containing the result value or an error variant containing an error description. Because the type system requires checking which variant is present before accessing the value, every call site must explicitly handle the error path.
In Helicone, the Result<T, E> type is used throughout the backend manager layer. Every manager method returns a Result, and controllers unwrap it to produce the appropriate HTTP response. This eliminates silent failures and makes error propagation explicit in the type signatures.
Usage
Use the Result type when:
- Operations can fail in expected ways (validation errors, not-found, permission denied).
- Callers must be forced to handle failure cases.
- Error information needs to be preserved and propagated through call chains.
- Exceptions are too coarse-grained or break control flow unpredictably.
Theoretical Basis
The Result type is a sum type from algebraic type theory, equivalent to Haskell's Either, Rust's Result, or OCaml's result. It leverages exhaustive pattern matching so the compiler rejects code that fails to handle a variant. This makes error handling total (every case is covered) rather than partial (some cases may be missed). The pattern follows the Railway-Oriented Programming metaphor, where computation proceeds along a success track until a failure shunts it onto the error track, and subsequent operations on the error track are no-ops.