Error Handling Patterns

Pony’s built-in error mechanism is deliberately simple: a partial function either succeeds or raises error, and the caller’s else block handles the failure. There’s no exception hierarchy, no error message, no way to distinguish one failure from another.

That simplicity is a feature — it keeps the runtime lean and the semantics clear. But when a function can fail for multiple distinct reasons, the caller often needs to know which reason. The patterns in this chapter use Pony’s type system to make error conditions explicit, typed, and compiler-checked.