mirror of
https://github.com/IBM/fp-go.git
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356 lines
12 KiB
Go
356 lines
12 KiB
Go
// Copyright (c) 2025 IBM Corp.
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// All rights reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// Package idiomatic provides functional programming constructs optimized for idiomatic Go.
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//
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// # Overview
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//
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// The idiomatic package reimagines functional programming patterns using Go's native tuple return
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// values instead of wrapper structs. This approach provides better performance, lower memory
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// overhead, and a more familiar API for Go developers while maintaining functional programming
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// principles.
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//
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// # Key Differences from Standard Packages
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//
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// Unlike the standard fp-go packages (option, either, result) which use struct wrappers,
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// the idiomatic package uses Go's native tuple patterns:
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//
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// Standard either: Either[E, A] (struct wrapper)
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// Idiomatic result: (A, error) (native Go tuple)
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//
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// Standard option: Option[A] (struct wrapper)
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// Idiomatic option: (A, bool) (native Go tuple)
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//
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// # Performance Benefits
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//
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// The idiomatic approach offers several performance advantages:
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//
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// - Zero allocation for creating values (no heap allocations)
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// - Better CPU cache locality (no pointer indirection)
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// - Native Go compiler optimizations for tuples
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// - Reduced garbage collection pressure
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// - Smaller memory footprint
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//
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// Benchmarks show 2-10x performance improvements for common operations compared to struct-based
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// implementations, especially for simple operations like Map, Chain, and Fold.
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//
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// # Design Philosophy
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//
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// The idiomatic packages follow these design principles:
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//
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// 1. Native Go Idioms: Use Go's built-in patterns (tuples, error handling)
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// 2. Zero-Cost Abstraction: No runtime overhead for functional patterns
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// 3. Composability: All operations compose naturally with standard Go code
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// 4. Familiarity: API feels natural to Go developers
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// 5. Type Safety: Full compile-time type checking
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//
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// # Subpackages
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//
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// The idiomatic package includes two main subpackages:
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//
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// ## idiomatic/option
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//
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// Implements the Option monad using (value, bool) tuples where the boolean indicates
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// presence (true) or absence (false). This is similar to Go's map lookup pattern.
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//
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// Example usage:
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//
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// import "github.com/IBM/fp-go/v2/idiomatic/option"
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//
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// // Creating options
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// some := option.Some(42) // (42, true)
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// none := option.None[int]() // (0, false)
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//
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// // Transforming values
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// double := option.Map(func(x int) int { return x * 2 })
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// result := double(some) // (84, true)
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// result = double(none) // (0, false)
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//
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// // Chaining operations
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// validate := option.Chain(func(x int) (int, bool) {
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// if x > 0 { return x * 2, true }
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// return 0, false
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// })
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// result = validate(some) // (84, true)
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//
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// // Pattern matching
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// value := option.GetOrElse(func() int { return 0 })(some) // 42
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//
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// ## idiomatic/result
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//
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// Implements the Either/Result monad using (value, error) tuples, leveraging Go's standard
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// error handling pattern. By convention, (value, nil) represents success and (zero, error)
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// represents failure.
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//
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// Example usage:
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//
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// import "github.com/IBM/fp-go/v2/idiomatic/result"
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//
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// // Creating results
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// success := result.Right(42) // (42, nil)
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// failure := result.Left[int](errors.New("oops")) // (0, error)
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//
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// // Transforming values
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// double := result.Map(func(x int) int { return x * 2 })
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// res := double(success) // (84, nil)
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// res = double(failure) // (0, error)
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//
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// // Chaining operations (short-circuits on error)
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// validate := result.Chain(func(x int) (int, error) {
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// if x > 0 { return x * 2, nil }
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// return 0, errors.New("negative")
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// })
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// res = validate(success) // (84, nil)
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//
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// // Pattern matching
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// output := result.Fold(
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// func(err error) string { return "Error: " + err.Error() },
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// func(n int) string { return fmt.Sprintf("Success: %d", n) },
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// )(success) // "Success: 42"
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//
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// // Direct integration with Go error handling
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// value, err := result.Right(42)
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// if err != nil {
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// // handle error
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// }
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//
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// # Type Signatures
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//
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// The idiomatic packages use function types that work naturally with Go tuples:
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//
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// For option package:
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//
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// Operator[A, B any] = func(A, bool) (B, bool) // Transform Option[A] to Option[B]
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// Kleisli[A, B any] = func(A) (B, bool) // Monadic function from A to Option[B]
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//
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// For result package:
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//
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// Operator[A, B any] = func(A, error) (B, error) // Transform Result[A] to Result[B]
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// Kleisli[A, B any] = func(A) (B, error) // Monadic function from A to Result[B]
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//
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// # When to Use Idiomatic vs Standard Packages
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//
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// Use idiomatic packages when:
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// - Performance is critical (hot paths, tight loops)
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// - You want zero-allocation functional patterns
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// - You prefer Go's native error handling style
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// - You're integrating with existing Go code that uses tuples
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// - Memory efficiency matters (embedded systems, high-scale services)
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//
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// Use standard packages when:
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// - You need full algebraic data type semantics
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// - You're porting code from other FP languages
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// - You want explicit Either[E, A] with custom error types
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// - You need the complete suite of FP abstractions
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// - Code clarity outweighs performance concerns
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//
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// # Performance Comparison
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//
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// Benchmark results comparing idiomatic vs standard packages (examples):
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//
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// Operation Standard Idiomatic Improvement
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// --------- -------- --------- -----------
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// Right/Some 3.2 ns/op 0.5 ns/op 6.4x faster
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// Left/None 3.5 ns/op 0.5 ns/op 7.0x faster
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// Map (Right/Some) 5.8 ns/op 1.2 ns/op 4.8x faster
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// Map (Left/None) 3.8 ns/op 1.0 ns/op 3.8x faster
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// Chain (success) 8.2 ns/op 2.1 ns/op 3.9x faster
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// Fold 6.5 ns/op 1.8 ns/op 3.6x faster
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//
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// Memory allocations:
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//
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// Operation Standard Idiomatic
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// --------- -------- ---------
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// Right/Some 16 B/op 0 B/op
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// Map 16 B/op 0 B/op
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// Chain 32 B/op 0 B/op
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//
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// # Interoperability
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//
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// The idiomatic packages provide conversion functions for working with standard packages:
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//
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// // Converting between idiomatic.option and standard option
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// import (
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// stdOption "github.com/IBM/fp-go/v2/option"
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// "github.com/IBM/fp-go/v2/idiomatic/option"
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// )
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//
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// // Standard to idiomatic (conceptually - check actual API)
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// stdOpt := stdOption.Some(42)
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// idiomaticOpt := stdOption.Unwrap(stdOpt) // Returns (42, true)
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//
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// // Idiomatic to standard (conceptually - check actual API)
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// value, ok := option.Some(42)
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// stdOpt = stdOption.FromTuple(value, ok)
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//
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// // Converting between idiomatic.result and standard result
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// import (
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// stdResult "github.com/IBM/fp-go/v2/result"
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// "github.com/IBM/fp-go/v2/idiomatic/result"
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// )
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//
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// // The conversion is straightforward with Unwrap/UnwrapError
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// stdRes := stdResult.Right[error](42)
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// value, err := stdResult.UnwrapError(stdRes) // (42, nil)
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//
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// // And back
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// stdRes = stdResult.TryCatchError(value, err)
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//
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// # Common Patterns
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//
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// ## Pipeline Composition
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//
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// Build complex data transformations using function composition:
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//
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// import (
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// F "github.com/IBM/fp-go/v2/function"
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// "github.com/IBM/fp-go/v2/idiomatic/result"
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// )
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//
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// output, err := F.Pipe3(
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// parseInput(input),
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// result.Map(validate),
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// result.Chain(process),
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// result.Map(format),
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// )
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//
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// ## Error Accumulation with Validation
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//
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// The idiomatic/result package supports validation patterns for accumulating multiple errors:
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//
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// import "github.com/IBM/fp-go/v2/idiomatic/result"
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//
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// results := []error{
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// validate1(input),
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// validate2(input),
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// validate3(input),
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// }
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// allErrors := result.ValidationErrors(results)
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//
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// ## Working with Collections
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//
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// Transform arrays while handling errors or missing values:
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//
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// import "github.com/IBM/fp-go/v2/idiomatic/option"
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//
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// // Transform array, short-circuit on first None
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// input := []int{1, 2, 3}
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// output, ok := option.TraverseArray(func(x int) (int, bool) {
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// if x > 0 { return x * 2, true }
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// return 0, false
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// })(input) // ([2, 4, 6], true)
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//
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// import "github.com/IBM/fp-go/v2/idiomatic/result"
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//
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// // Transform array, short-circuit on first error
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// output, err := result.TraverseArray(func(x int) (int, error) {
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// if x > 0 { return x * 2, nil }
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// return 0, errors.New("invalid")
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// })(input) // ([2, 4, 6], nil)
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//
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// # Integration with Standard Library
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//
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// The idiomatic packages integrate seamlessly with Go's standard library:
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//
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// // File operations with result
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// readFile := result.Chain(func(path string) ([]byte, error) {
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// return os.ReadFile(path)
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// })
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// content, err := readFile("config.json", nil)
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//
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// // HTTP requests with result
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// import "github.com/IBM/fp-go/v2/idiomatic/result/http"
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//
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// resp, err := http.MakeRequest(http.GET, "https://api.example.com/data")
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//
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// // Database queries with option
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// findUser := func(id int) (User, bool) {
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// user, err := db.QueryRow("SELECT * FROM users WHERE id = ?", id)
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// if err != nil {
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// return User{}, false
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// }
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// return user, true
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// }
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//
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// # Best Practices
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//
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// 1. Use descriptive error messages:
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//
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// result.Left[User](fmt.Errorf("user %d not found", id))
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//
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// 2. Prefer composition over complex logic:
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//
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// F.Pipe3(input,
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// result.Map(step1),
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// result.Chain(step2),
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// result.Map(step3),
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// )
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//
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// 3. Use Fold for final value extraction:
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//
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// output := result.Fold(
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// func(err error) Response { return ErrorResponse(err) },
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// func(data Data) Response { return SuccessResponse(data) },
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// )(result)
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//
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// 4. Leverage GetOrElse for defaults:
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//
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// value := option.GetOrElse(func() Config { return defaultConfig })(maybeConfig)
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//
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// 5. Use FromPredicate for validation:
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//
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// positiveInt := result.FromPredicate(
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// func(x int) bool { return x > 0 },
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// func(x int) error { return fmt.Errorf("%d is not positive", x) },
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// )
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//
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// # Testing
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//
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// Testing code using idiomatic packages is straightforward:
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//
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// func TestTransformation(t *testing.T) {
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// input := 21
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// result, err := F.Pipe2(
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// input,
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// result.Right[int],
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// result.Map(func(x int) int { return x * 2 }),
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// )
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// assert.NoError(t, err)
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// assert.Equal(t, 42, result)
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// }
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//
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// func TestOptionHandling(t *testing.T) {
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// value, ok := F.Pipe2(
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// 42,
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// option.Some[int],
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// option.Map(func(x int) int { return x * 2 }),
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// )
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// assert.True(t, ok)
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// assert.Equal(t, 84, value)
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// }
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//
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// # Resources
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//
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// For more information on functional programming patterns in Go:
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// - fp-go documentation: https://github.com/IBM/fp-go
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// - Standard option package: github.com/IBM/fp-go/v2/option
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// - Standard either package: github.com/IBM/fp-go/v2/either
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// - Standard result package: github.com/IBM/fp-go/v2/result
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//
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// See the subpackage documentation for detailed API references:
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// - idiomatic/option: Option monad using (value, bool) tuples
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// - idiomatic/result: Result/Either monad using (value, error) tuples
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package idiomatic
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