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Implement v2 using type aliases (#141)
* fix: initial checkin of v2 Signed-off-by: Dr. Carsten Leue <carsten.leue@de.ibm.com> * fix: slowly migrate IO Signed-off-by: Dr. Carsten Leue <carsten.leue@de.ibm.com> * fix: migrate MonadTraverseArray and TraverseArray Signed-off-by: Dr. Carsten Leue <carsten.leue@de.ibm.com> * fix: migrate traversal Signed-off-by: Dr. Carsten Leue <carsten.leue@de.ibm.com> * fix: complete migration of IO Signed-off-by: Dr. Carsten Leue <carsten.leue@de.ibm.com> * fix: migrate ioeither Signed-off-by: Dr. Carsten Leue <carsten.leue@de.ibm.com> * fix: refactorY Signed-off-by: Dr. Carsten Leue <carsten.leue@de.ibm.com> * fix: next step in migration Signed-off-by: Dr. Carsten Leue <carsten.leue@de.ibm.com> * fix: adjust IO generation code Signed-off-by: Dr. Carsten Leue <carsten.leue@de.ibm.com> * fix: get rid of more IO methods Signed-off-by: Dr. Carsten Leue <carsten.leue@de.ibm.com> * fix: get rid of more IO * fix: convert iooption Signed-off-by: Dr. Carsten Leue <carsten.leue@de.ibm.com> * fix: convert reader Signed-off-by: Dr. Carsten Leue <carsten.leue@de.ibm.com> * fix: convert a bit of reader Signed-off-by: Dr. Carsten Leue <carsten.leue@de.ibm.com> * fix: new build script Signed-off-by: Dr. Carsten Leue <carsten.leue@de.ibm.com> * fix: cleanup Signed-off-by: Dr. Carsten Leue <carsten.leue@de.ibm.com> * fix: reformat Signed-off-by: Dr. Carsten Leue <carsten.leue@de.ibm.com> * fix: simplify Signed-off-by: Dr. Carsten Leue <carsten.leue@de.ibm.com> * fix: some cleanup Signed-off-by: Dr. Carsten Leue <carsten.leue@de.ibm.com> * fix: adjust Pair to Haskell semantic Signed-off-by: Dr. Carsten Leue <carsten.leue@de.ibm.com> * fix: documentation and testcases Signed-off-by: Dr. Carsten Leue <carsten.leue@de.ibm.com> * fix: some performance optimizations Signed-off-by: Dr. Carsten Leue <carsten.leue@de.ibm.com> * fix: remove coverage Signed-off-by: Dr. Carsten Leue <carsten.leue@de.ibm.com> * fix: better doc Signed-off-by: Dr. Carsten Leue <carsten.leue@de.ibm.com> --------- Signed-off-by: Dr. Carsten Leue <carsten.leue@de.ibm.com>
This commit is contained in:
Carsten Leue
GitHub
236
v2/function/function.go
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236
v2/function/function.go
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// Copyright (c) 2023 - 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 function
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// Identity returns its argument unchanged.
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//
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// This is the identity function from category theory, which satisfies:
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// - Identity(x) = x for all x
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//
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// It's useful as a default transformation or when you need a function that
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// does nothing but is required by an API.
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//
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// Example:
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//
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// result := Identity(42) // 42
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// result := Identity("hello") // "hello"
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//
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// // Useful in higher-order functions
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// values := []int{1, 2, 3}
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// mapped := Map(Identity[int])(values) // [1, 2, 3]
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func Identity[A any](a A) A {
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return a
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}
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// Constant creates a nullary function that always returns the same value.
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//
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// This creates a function with no parameters that returns the constant value 'a'.
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// Useful for lazy evaluation or when you need a function that produces a fixed value.
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//
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// Parameters:
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// - a: The constant value to return
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//
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// Returns:
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// - A function that takes no arguments and returns 'a'
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//
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// Example:
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//
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// getFortyTwo := Constant(42)
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// result := getFortyTwo() // 42
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//
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// getMessage := Constant("Hello")
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// msg := getMessage() // "Hello"
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func Constant[A any](a A) func() A {
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return func() A {
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return a
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}
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}
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// Constant1 creates a unary function that always returns the same value, ignoring its input.
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//
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// This creates a function that takes one parameter but ignores it and always returns
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// the constant value 'a'. Useful for providing default values or placeholder functions.
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//
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// Type Parameters:
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// - B: The type of the ignored input parameter
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// - A: The type of the constant return value
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//
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// Parameters:
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// - a: The constant value to return
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//
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// Returns:
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// - A function that takes a B and returns 'a'
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//
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// Example:
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//
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// alwaysZero := Constant1[string, int](0)
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// result := alwaysZero("anything") // 0
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//
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// defaultName := Constant1[int, string]("Unknown")
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// name := defaultName(42) // "Unknown"
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func Constant1[B, A any](a A) func(B) A {
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return func(_ B) A {
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return a
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}
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}
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// Constant2 creates a binary function that always returns the same value, ignoring its inputs.
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//
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// This creates a function that takes two parameters but ignores both and always returns
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// the constant value 'a'.
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//
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// Type Parameters:
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// - B: The type of the first ignored input parameter
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// - C: The type of the second ignored input parameter
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// - A: The type of the constant return value
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//
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// Parameters:
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// - a: The constant value to return
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//
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// Returns:
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// - A function that takes a B and C and returns 'a'
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//
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// Example:
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//
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// alwaysTrue := Constant2[int, string, bool](true)
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// result := alwaysTrue(42, "test") // true
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func Constant2[B, C, A any](a A) func(B, C) A {
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return func(_ B, _ C) A {
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return a
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}
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}
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// IsNil checks if a pointer is nil.
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//
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// Parameters:
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// - a: A pointer to check
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//
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// Returns:
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// - true if the pointer is nil, false otherwise
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//
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// Example:
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//
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// var ptr *int
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// IsNil(ptr) // true
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//
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// value := 42
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// IsNil(&value) // false
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func IsNil[A any](a *A) bool {
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return a == nil
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}
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// IsNonNil checks if a pointer is not nil.
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//
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// This is the logical negation of IsNil.
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//
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// Parameters:
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// - a: A pointer to check
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//
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// Returns:
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// - true if the pointer is not nil, false otherwise
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//
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// Example:
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//
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// var ptr *int
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// IsNonNil(ptr) // false
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//
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// value := 42
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// IsNonNil(&value) // true
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func IsNonNil[A any](a *A) bool {
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return a != nil
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}
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// Swap returns a new binary function with the parameter order reversed.
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//
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// Given a function f(a, b), Swap returns a function g(b, a) where g(b, a) = f(a, b).
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// This is useful when you have a function but need to call it with arguments in
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// a different order.
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//
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// Type Parameters:
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// - T1: The type of the first parameter (becomes second)
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// - T2: The type of the second parameter (becomes first)
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// - R: The return type
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//
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// Parameters:
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// - f: The function to swap
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//
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// Returns:
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// - A new function with swapped parameters
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//
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// Example:
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//
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// divide := func(a, b float64) float64 { return a / b }
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// divideSwapped := Swap(divide)
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//
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// result1 := divide(10, 2) // 5.0 (10 / 2)
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// result2 := divideSwapped(10, 2) // 0.2 (2 / 10)
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//
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// subtract := func(a, b int) int { return a - b }
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// subtractSwapped := Swap(subtract)
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// result := subtractSwapped(5, 10) // 5 (10 - 5)
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func Swap[T1, T2, R any](f func(T1, T2) R) func(T2, T1) R {
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return func(t2 T2, t1 T1) R {
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return f(t1, t2)
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}
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}
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// First returns the first of two input values, ignoring the second.
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//
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// This is a projection function that selects the first element of a pair.
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// Also known as the K combinator in combinatory logic.
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//
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// Type Parameters:
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// - T1: The type of the first value (returned)
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// - T2: The type of the second value (ignored)
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//
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// Parameters:
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// - t1: The first value
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// - t2: The second value (ignored)
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//
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// Returns:
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// - The first value
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//
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// Example:
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//
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// result := First(42, "hello") // 42
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// result := First(true, 100) // true
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func First[T1, T2 any](t1 T1, _ T2) T1 {
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return t1
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}
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// Second returns the second of two input values, ignoring the first.
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//
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// This is a projection function that selects the second element of a pair.
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// Identical to SK combinator in combinatory logic.
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//
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// Type Parameters:
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// - T1: The type of the first value (ignored)
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// - T2: The type of the second value (returned)
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//
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// Parameters:
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// - t1: The first value (ignored)
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// - t2: The second value
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//
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// Returns:
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// - The second value
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//
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// Example:
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//
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// result := Second(42, "hello") // "hello"
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// result := Second(true, 100) // 100
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func Second[T1, T2 any](_ T1, t2 T2) T2 {
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return t2
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}
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