golang-samber-mo

Q: How do I install golang-samber-mo?

Run npx skills add https://github.com/samber/cc-skills-golang --skill golang-samber-mo in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/golang-samber-mo/ (personal) or .claude/skills/golang-samber-mo/ (project).

by samberBackend & APIs

Monadic types for Golang using samber/mo — Option, Result, Either, Future, IO, Task, and State types for type-safe nullable values, error handling, and functional composition with pipeline sub-packages. Apply when using or adopting samber/mo, when the codebase imports github.com/samber/mo, or when considering functional programming patterns as a safety design for Golang. Not for nil-safety and zero-value design without this library (→ See samber/cc-skills-golang@golang-safety skill), nor for native error wrapping with fmt.Errorf, errors.Is and errors.As (→ See samber/cc-skills-golang@golang-error-handling skill).

Installs: 38.4K
Last 24h: +151
Trending rank: #1477
Security: Pass

Install

Works with every agent the skills CLI supports.

npx skills add https://github.com/samber/cc-skills-golang --skill golang-samber-mo

01
Install
Run the command in your project. The CLI asks which agents to install for.
02
Describe the task
Ask your agent for something this skill covers. It loads golang-samber-mo automatically when relevant.
03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.

Security audits

Independent scans of the skill's instructions and bundled files.

Gen Agent Trust Hub PassSAFE ·This skill provides documentation and best practices for the 'samber/mo' Go library, which implements functional programming types like Option and Result. It focuses on improving code safety through type-safe nil handling and error propagation, and no security risks were identified.

Socket PassNo alerts

Snyk PassLOW ·Risk: LOW · No issues

ZeroLeaks PassNONE ·Score: 93/100 · 2 sections analyzed

SKILL.md

The instructions your agent reads when the skill is triggered.

Persona: You are a Go engineer bringing functional programming safety to Go. You use monads to make impossible states unrepresentable — nil checks become type constraints, error handling becomes composable pipelines.

Thinking mode: Reason as thoroughly as possible when designing multi-step Option/Result/Either pipelines — wrong type choice creates unnecessary wrapping/unwrapping that defeats the purpose of monads. On Claude Code, use ultrathink to trigger extended thinking explicitly.

samber/mo — Monads and Functional Abstractions for Go

Go 1.18+ library providing type-safe monadic types with zero dependencies. Inspired by Scala, Rust, and fp-ts.

Official Resources:

This skill is not exhaustive — refer to library documentation and code examples for more information:

For Go package docs, symbols, versions, importers, and known vulnerabilities, → See samber/cc-skills-golang@golang-pkg-go-dev skill (godig), preferred over Context7 for Go package facts.
To navigate this library's usage in your own code (definitions, call sites, diagnostics), → See samber/cc-skills-golang@golang-gopls skill (gopls).
Context7 remains a fallback for docs not indexed on pkg.go.dev.

go get github.com/samber/mo

For an introduction to functional programming concepts and why monads are valuable in Go, see Monads Guide.

Core Types at a Glance

Type	Purpose	Think of it as...
`Option[T]`	Value that may be absent	Rust's `Option`, Java's `Optional`
`Result[T]`	Operation that may fail	Rust's `Result<T, E>`, replaces `(T, error)`
`Either[L, R]`	Value of one of two types	Scala's `Either`, TypeScript discriminated union
`EitherX[L, R]`	Value of one of X types	Scala's `Either`, TypeScript discriminated union
`Future[T]`	Async value not yet available	JavaScript `Promise`
`IO[T]`	Lazy synchronous side effect	Haskell's `IO`
`Task[T]`	Lazy async computation	fp-ts `Task`
`State[S, A]`	Stateful computation	Haskell's `State` monad

Option[T] — Nullable Values Without nil

Represents a value that is either present (Some) or absent (None). Eliminates nil pointer risks at the type level.

import "github.com/samber/mo"

name := mo.Some("Alice")          // Option[string] with value
empty := mo.None[string]()        // Option[string] without value
fromPtr := mo.PointerToOption(ptr) // nil pointer -> None

// Safe extraction
name.OrElse("Anonymous")  // "Alice"
empty.OrElse("Anonymous")  // "Anonymous"

// Transform if present, skip if absent
upper := name.Map(func(s string) (string, bool) {
    return strings.ToUpper(s), true
})

Key methods: Some, None, Get, MustGet, OrElse, OrEmpty, Map, FlatMap, Match, ForEach, ToPointer, IsPresent, IsAbsent.

Option implements json.Marshaler/Unmarshaler, sql.Scanner, driver.Valuer — use it directly in JSON structs and database models.

For full API reference, see Option Reference.

Result[T] — Error Handling as Values

Represents success (Ok) or failure (Err). Equivalent to Either[error, T] but specialized for Go's error pattern.

// Wrap Go's (value, error) pattern
result := mo.TupleToResult(os.ReadFile("config.yaml"))

// Same-type transform — errors short-circuit automatically
upper := mo.Ok("hello").Map(func(s string) (string, error) {
    return strings.ToUpper(s), nil
})
// Ok("HELLO")

// Extract with fallback
val := upper.OrElse("default")

Go limitation: Direct methods (.Map, .FlatMap) cannot change the type parameter — Result[T].Map returns Result[T], not Result[U]. Go methods cannot introduce new type parameters. For type-changing transforms (e.g. Result[[]byte] to Result[Config]), use sub-package functions or mo.Do:

import "github.com/samber/mo/result"

// Type-changing pipeline: []byte -> Config -> ValidConfig
parsed := result.Pipe2(
    mo.TupleToResult(os.ReadFile("config.yaml")),
    result.Map(func(data []byte) Config { return parseConfig(data) }),
    result.FlatMap(func(cfg Config) mo.Result[ValidConfig] { return validate(cfg) }),
)

Key methods: Ok, Err, Errf, TupleToResult, Try, Get, MustGet, OrElse, Map, FlatMap, MapErr, Match, ForEach, ToEither, IsOk, IsError.

For full API reference, see Result Reference.

Either[L, R] — Discriminated Union of Two Types

Represents a value that is one of two possible types. Unlike Result, neither side implies success or failure — both are valid alternatives.

// API that returns either cached data or fresh data
func fetchUser(id string) mo.Either[CachedUser, FreshUser] {
    if cached, ok := cache.Get(id); ok {
        return mo.Left[CachedUser, FreshUser](cached)
    }
    return mo.Right[CachedUser, FreshUser](db.Fetch(id))
}

// Pattern match
result := fetchUser("user-123")
result.Match(
    func(cached CachedUser) mo.Either[CachedUser, FreshUser] { /* use cached */ },
    func(fresh FreshUser) mo.Either[CachedUser, FreshUser] { /* use fresh */ },
)

When to use Either vs Result: Use Result[T] when one path is an error. Use Either[L, R] when both paths are valid alternatives (cached vs fresh, left vs right, strategy A vs B).

Either3[T1, T2, T3], Either4, and Either5 extend this to 3-5 type variants.

For full API reference, see Either Reference.

Do Notation — Imperative Style with Monadic Safety

mo.Do wraps imperative code in a Result, catching panics from MustGet() calls:

result := mo.Do(func() int {
    // MustGet panics on None/Err — Do catches it as Result error
    a := mo.Some(21).MustGet()
    b := mo.Ok(2).MustGet()
    return a * b  // 42
})
// result is Ok(42)

result := mo.Do(func() int {
    val := mo.None[int]().MustGet()  // panics
    return val
})
// result is Err("no such element")

Do notation bridges imperative Go style with monadic safety — write straight-line code, get automatic error propagation.

Pipeline Sub-Packages vs Direct Chaining

samber/mo provides two ways to compose operations:

Direct methods (.Map, .FlatMap) — work when the output type equals the input type:

opt := mo.Some(42)
doubled := opt.Map(func(v int) (int, bool) {
    return v * 2, true
})  // Option[int]

Sub-package functions (option.Map, result.Map) — required when the output type differs from input:

import "github.com/samber/mo/option"

// int -> string type change: use sub-package Map
strOpt := option.Map(func(v int) string {
    return fmt.Sprintf("value: %d", v)
})(mo.Some(42))  // Option[string]

Pipe functions (option.Pipe3, result.Pipe3) — chain multiple type-changing transformations readably:

import "github.com/samber/mo/option"

result := option.Pipe3(
    mo.Some(42),
    option.Map(func(v int) string { return strconv.Itoa(v) }),
    option.Map(func(s string) []byte { return []byte(s) }),
    option.FlatMap(func(b []byte) mo.Option[string] {
        if len(b) > 0 { return mo.Some(string(b)) }
        return mo.None[string]()
    }),
)

Rule of thumb: Use direct methods for same-type transforms. Use sub-package functions + pipes when types change across steps.

For detailed pipeline API reference, see Pipelines Reference.

Common Patterns

JSON API responses with Option

type UserResponse struct {
    Name     string            `json:"name"`
    Nickname mo.Option[string] `json:"nickname"`  // omits null gracefully
    Bio      mo.Option[string] `json:"bio"`
}

Database nullable columns

type User struct {
    ID       int
    Email    string
    Phone    mo.Option[string]  // implements sql.Scanner + driver.Valuer
}

err := row.Scan(&u.ID, &u.Email, &u.Phone)

Wrapping existing Go APIs

// Convert map lookup to Option
func MapGet[K comparable, V any](m map[K]V, key K) mo.Option[V] {
    return mo.TupleToOption(m[key])  // m[key] returns (V, bool)
}

Uniform extraction with Fold

mo.Fold works uniformly across Option, Result, and Either via the Foldable interface:

str := mo.Fold[error, int, string](
    mo.Ok(42),  // works with Option, Result, or Either
    func(v int) string { return fmt.Sprintf("got %d", v) },
    func(err error) string { return "failed" },
)
// "got 42"

Best Practices

Prefer OrElse over MustGet — MustGet panics on absent/error values; use it only inside mo.Do blocks where panics are caught, or when you are certain the value exists
Use TupleToResult at API boundaries — convert Go's (T, error) to Result[T] at the boundary, then chain with Map/FlatMap inside your domain logic
Use Result[T] for errors, Either[L, R] for alternatives — Result is specialized for success/failure; Either is for two valid types
Option for nullable fields, not zero values — Option[string] distinguishes "absent" from "empty string"; use plain string when empty string is a valid value
Chain, don't nest — result.Map(...).FlatMap(...).OrElse(default) reads left-to-right; avoid nested if/else patterns when monadic chaining is cleaner
Use sub-package pipes for multi-step type transformations — when 3+ steps each change the type, option.Pipe3(...) is more readable than nested function calls

For advanced types (Future, IO, Task, State), see Advanced Types Reference.

If you encounter a bug or unexpected behavior in samber/mo, open an issue at https://github.com/samber/mo/issues.

Cross-References

→ See samber/cc-skills-golang@golang-samber-lo skill for functional collection transforms (Map, Filter, Reduce on slices) that compose with mo types
→ See samber/cc-skills-golang@golang-error-handling skill for idiomatic Go error handling patterns
→ See samber/cc-skills-golang@golang-safety skill for nil-safety and defensive Go coding
→ See samber/cc-skills-golang@golang-database skill for database access patterns
→ See samber/cc-skills-golang@golang-design-patterns skill for functional options and other Go patterns

FAQ

What does the golang-samber-mo skill do?

How do I install golang-samber-mo?

Run npx skills add https://github.com/samber/cc-skills-golang --skill golang-samber-mo in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/golang-samber-mo/ (personal) or .claude/skills/golang-samber-mo/ (project).

Which AI agents can use golang-samber-mo?

Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.

Is golang-samber-mo safe to install?

Security partners have reviewed it: Gen Agent Trust Hub passed; Socket passed; Snyk passed; ZeroLeaks passed. As with any skill, read the SKILL.md and bundled scripts before installing.

Who maintains golang-samber-mo?

It is published by samber in samber/cc-skills-golang. It has 38,358 recorded installs.

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golang-samber-mo

Install

Install

Describe the task

Review the result

Security audits

SKILL.md

samber/mo — Monads and Functional Abstractions for Go

Core Types at a Glance

Option[T] — Nullable Values Without nil

Result[T] — Error Handling as Values

Either[L, R] — Discriminated Union of Two Types

Do Notation — Imperative Style with Monadic Safety

Pipeline Sub-Packages vs Direct Chaining

Common Patterns

JSON API responses with Option

Database nullable columns

Wrapping existing Go APIs

Uniform extraction with Fold

Best Practices

Cross-References

FAQ

More from samber/cc-skills-golang

Popular backend & apis skills