mirror of
https://github.com/IBM/fp-go.git
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304 lines
8.4 KiB
Go
304 lines
8.4 KiB
Go
// 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 ioeither
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import (
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"github.com/IBM/fp-go/v2/internal/apply"
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"github.com/IBM/fp-go/v2/internal/chain"
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"github.com/IBM/fp-go/v2/internal/functor"
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L "github.com/IBM/fp-go/v2/optics/lens"
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)
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// Do creates an empty context of type [S] to be used with the [Bind] operation.
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// This is the starting point for do-notation style composition.
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//
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// Example:
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//
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// type State struct {
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// User User
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// Posts []Post
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// }
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// result := ioeither.Do[error](State{})
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func Do[E, S any](
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empty S,
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) IOEither[E, S] {
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return Of[E](empty)
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}
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// Bind attaches the result of a computation to a context [S1] to produce a context [S2].
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// This enables sequential composition where each step can depend on the results of previous steps.
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//
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// The setter function takes the result of the computation and returns a function that
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// updates the context from S1 to S2.
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//
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// Example:
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//
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// type State struct {
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// User User
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// Posts []Post
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// }
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//
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// result := F.Pipe2(
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// ioeither.Do[error](State{}),
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// ioeither.Bind(
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// func(user User) func(State) State {
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// return func(s State) State { s.User = user; return s }
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// },
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// func(s State) ioeither.IOEither[error, User] {
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// return ioeither.TryCatch(func() (User, error) {
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// return fetchUser()
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// })
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// },
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// ),
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// ioeither.Bind(
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// func(posts []Post) func(State) State {
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// return func(s State) State { s.Posts = posts; return s }
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// },
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// func(s State) ioeither.IOEither[error, []Post] {
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// // This can access s.User from the previous step
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// return ioeither.TryCatch(func() ([]Post, error) {
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// return fetchPostsForUser(s.User.ID)
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// })
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// },
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// ),
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// )
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func Bind[E, S1, S2, T any](
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setter func(T) func(S1) S2,
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f func(S1) IOEither[E, T],
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) Operator[E, S1, S2] {
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return chain.Bind(
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Chain[E, S1, S2],
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Map[E, T, S2],
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setter,
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f,
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)
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}
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// Let attaches the result of a computation to a context [S1] to produce a context [S2]
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func Let[E, S1, S2, T any](
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setter func(T) func(S1) S2,
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f func(S1) T,
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) Operator[E, S1, S2] {
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return functor.Let(
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Map[E, S1, S2],
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setter,
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f,
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)
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}
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// LetTo attaches the a value to a context [S1] to produce a context [S2]
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func LetTo[E, S1, S2, T any](
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setter func(T) func(S1) S2,
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b T,
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) Operator[E, S1, S2] {
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return functor.LetTo(
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Map[E, S1, S2],
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setter,
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b,
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)
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}
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// BindTo initializes a new state [S1] from a value [T]
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func BindTo[E, S1, T any](
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setter func(T) S1,
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) Operator[E, T, S1] {
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return chain.BindTo(
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Map[E, T, S1],
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setter,
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)
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}
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// ApS attaches a value to a context [S1] to produce a context [S2] by considering
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// the context and the value concurrently (using Applicative rather than Monad).
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// This allows independent computations to be combined without one depending on the result of the other.
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//
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// Unlike Bind, which sequences operations, ApS can be used when operations are independent
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// and can conceptually run in parallel.
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//
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// Example:
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//
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// type State struct {
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// User User
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// Posts []Post
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// }
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//
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// // These operations are independent and can be combined with ApS
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// getUser := ioeither.Right[error](User{ID: 1, Name: "Alice"})
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// getPosts := ioeither.Right[error]([]Post{{ID: 1, Title: "Hello"}})
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//
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// result := F.Pipe2(
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// ioeither.Do[error](State{}),
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// ioeither.ApS(
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// func(user User) func(State) State {
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// return func(s State) State { s.User = user; return s }
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// },
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// getUser,
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// ),
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// ioeither.ApS(
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// func(posts []Post) func(State) State {
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// return func(s State) State { s.Posts = posts; return s }
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// },
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// getPosts,
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// ),
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// )
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func ApS[E, S1, S2, T any](
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setter func(T) func(S1) S2,
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fa IOEither[E, T],
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) Operator[E, S1, S2] {
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return apply.ApS(
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Ap[S2, E, T],
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Map[E, S1, func(T) S2],
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setter,
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fa,
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)
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}
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// ApSL attaches a value to a context using a lens-based setter.
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// This is a convenience function that combines ApS with a lens, allowing you to use
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// optics to update nested structures in a more composable way.
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//
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// The lens parameter provides both the getter and setter for a field within the structure S.
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// This eliminates the need to manually write setter functions.
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//
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// Example:
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//
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// type Config struct {
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// Host string
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// Port int
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// }
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//
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// portLens := lens.MakeLens(
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// func(c Config) int { return c.Port },
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// func(c Config, p int) Config { c.Port = p; return c },
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// )
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//
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// result := F.Pipe2(
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// ioeither.Of[error](Config{Host: "localhost"}),
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// ioeither.ApSL(portLens, ioeither.Of[error](8080)),
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// )
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func ApSL[E, S, T any](
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lens L.Lens[S, T],
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fa IOEither[E, T],
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) Operator[E, S, S] {
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return ApS(lens.Set, fa)
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}
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// BindL attaches the result of a computation to a context using a lens-based setter.
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// This is a convenience function that combines Bind with a lens, allowing you to use
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// optics to update nested structures based on their current values.
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//
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// The lens parameter provides both the getter and setter for a field within the structure S.
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// The computation function f receives the current value of the focused field and returns
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// an IOEither that produces the new value.
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//
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// Example:
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//
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// type Counter struct {
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// Value int
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// }
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//
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// valueLens := lens.MakeLens(
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// func(c Counter) int { return c.Value },
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// func(c Counter, v int) Counter { c.Value = v; return c },
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// )
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//
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// increment := func(v int) ioeither.IOEither[error, int] {
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// return ioeither.TryCatch(func() (int, error) {
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// if v >= 100 {
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// return 0, errors.New("overflow")
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// }
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// return v + 1, nil
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// })
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// }
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//
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// result := F.Pipe1(
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// ioeither.Of[error](Counter{Value: 42}),
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// ioeither.BindL(valueLens, increment),
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// )
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func BindL[E, S, T any](
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lens L.Lens[S, T],
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f func(T) IOEither[E, T],
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) Operator[E, S, S] {
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return Bind[E, S, S, T](lens.Set, func(s S) IOEither[E, T] {
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return f(lens.Get(s))
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})
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}
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// LetL attaches the result of a pure computation to a context using a lens-based setter.
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// This is a convenience function that combines Let with a lens, allowing you to use
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// optics to update nested structures with pure transformations.
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//
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// The lens parameter provides both the getter and setter for a field within the structure S.
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// The transformation function f receives the current value of the focused field and returns
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// the new value directly (not wrapped in IOEither).
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//
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// Example:
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//
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// type Counter struct {
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// Value int
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// }
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//
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// valueLens := lens.MakeLens(
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// func(c Counter) int { return c.Value },
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// func(c Counter, v int) Counter { c.Value = v; return c },
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// )
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//
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// double := func(v int) int { return v * 2 }
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//
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// result := F.Pipe1(
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// ioeither.Of[error](Counter{Value: 21}),
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// ioeither.LetL(valueLens, double),
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// )
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func LetL[E, S, T any](
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lens L.Lens[S, T],
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f func(T) T,
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) Operator[E, S, S] {
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return Let[E, S, S, T](lens.Set, func(s S) T {
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return f(lens.Get(s))
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})
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}
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// LetToL attaches a constant value to a context using a lens-based setter.
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// This is a convenience function that combines LetTo with a lens, allowing you to use
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// optics to set nested fields to specific values.
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//
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// The lens parameter provides the setter for a field within the structure S.
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// Unlike LetL which transforms the current value, LetToL simply replaces it with
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// the provided constant value b.
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//
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// Example:
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//
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// type Config struct {
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// Debug bool
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// Timeout int
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// }
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//
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// debugLens := lens.MakeLens(
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// func(c Config) bool { return c.Debug },
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// func(c Config, d bool) Config { c.Debug = d; return c },
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// )
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//
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// result := F.Pipe1(
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// ioeither.Of[error](Config{Debug: true, Timeout: 30}),
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// ioeither.LetToL(debugLens, false),
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// )
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func LetToL[E, S, T any](
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lens L.Lens[S, T],
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b T,
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) Operator[E, S, S] {
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return LetTo[E, S, S, T](lens.Set, b)
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}
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