Validated (error accumulation) vs Result (fail-fast)

Context

The library includes two types for modelling operations that can fail: Result<V, E> and Validated<E, A>. A new user may be confused about when to use each one.

Decision

• Validated<E, A>: applicative-style error accumulation — all errors are collected before returning.
• Result<V, E>: fail-fast — the first error stops the chain.

Consequences

Positive:

• Each type has clear semantics and does not try to do both things.
• Validated is ideal for form/DTO validation where the user needs to see all errors at once.
• Result is ideal for business pipelines where an intermediate error makes continuing pointless.

Negative / tradeoffs:

• Two types that “look” similar can confuse users coming from other libraries (e.g., Vavr only has Validation).
• The user must learn when to use each one.

Alternatives considered

• A single type with a configurable mode: increases API complexity.
• Only Result: does not model accumulative validation well without losing the first error.