dry-monads
Functional programming primitives for Ruby — Result (Success/Failure), Maybe (Some/None), Try, Task, and List monads. dry-monads enables railway-oriented programming in Ruby: chain operations where each step can succeed or fail, automatically propagating failures without nested if/else or exception handling. The `do` notation (Dry::Monads::Do) enables clean sequential composition with automatic failure propagation — like async/await but for Result types. Used extensively in Hanami and dry-transaction for composing service objects.
Score Breakdown
⚙ Agent Friendliness
🔒 Security
No network exposure. Explicit error propagation reduces silent failure security risks. Failure values make error paths auditable. No side effects in pure monadic chains.
⚡ Reliability
Best When
You're building complex Ruby service objects or workflows with multi-step error paths and want explicit, composable error handling without exception-based control flow.
Avoid When
Your team isn't familiar with functional programming, you're doing simple Rails CRUD (ActiveRecord exceptions are sufficient), or you need async concurrency (dry-monads is synchronous).
Use Cases
- • Compose multi-step agent workflows in Ruby using Result monad railway — each step returns Success or Failure; the chain stops at first Failure without nested rescue blocks
- • Handle nullable agent data without nil checks using Maybe monad — Some(value) or None propagate through map/bind chains; eliminates NoMethodError on nil in agent data pipelines
- • Build agent service objects with dry-transaction using do notation — each step in the transaction is a Result-returning method; automatic rollback on Failure
- • Wrap risky agent operations (external API calls, file IO) in Try monad — converts exceptions to Failure(exception) values for composable error handling
- • Use Success/Failure pattern matching in Ruby 3.x — dry-monads' Result works with Ruby's case/in pattern matching for ergonomic success/failure branching
Not For
- • Teams unfamiliar with functional programming concepts — monads have a learning curve; developers expecting exception-based error handling find do-notation confusing initially
- • Simple Ruby scripts or models with straightforward logic — the overhead of Result/Maybe types isn't justified for simple CRUD operations without complex error propagation chains
- • Async/concurrent operations — dry-monads are synchronous; use concurrent-ruby, Ractor, or Async gem for concurrent agent operations
Interface
Authentication
Functional programming library — no auth concepts.
Pricing
dry-monads is MIT licensed, maintained by the dry-rb organization. Free for all use.
Agent Metadata
Known Gotchas
- ⚠ include Dry::Monads[:result, :do] required per class — monads and do notation must be explicitly included in each class that uses them; forgetting inclusion causes undefined method errors for Success/Failure/yield
- ⚠ Do notation yield (not keyword yield) — `value = yield step()` in do notation is not Ruby's block yield; it's dry-monads' Do module method; mixing with actual block yields causes confusing behavior
- ⚠ Failure propagates but exceptions don't — Try monad wraps exceptions as Failure; but exceptions raised inside Success/Failure chains (not via Try) still propagate as exceptions and bypass monad railway
- ⚠ Pattern matching requires Ruby 3.0+ — `case result; in Success(value)` uses Ruby 3.x pattern matching; older Ruby requires .fmap/.or_else chaining; check Ruby version compatibility for codebase
- ⚠ dry-transaction vs dry-monads directly — dry-transaction provides step-by-step DSL for service objects with automatic rollback; dry-monads is lower-level; don't reinvent dry-transaction with raw dry-monads do notation
- ⚠ Nested do notation blocks — multiple levels of yielded operations in nested methods; Halt exception from inner do propagates outward; ensure top-level entry point rescues Dry::Monads::Do::Halt and converts to Failure result
Alternatives
Full Evaluation Report
Detailed scoring breakdown, competitive positioning, security analysis, and improvement recommendations for dry-monads.
Scores are editorial opinions as of 2026-03-06.