mirror of
https://github.com/IBM/fp-go.git
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364 lines
9.9 KiB
Go
364 lines
9.9 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 reader
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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/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 the do-notation style of composing Reader computations.
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//
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// Example:
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//
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// type State struct {
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// Name string
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// Age int
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// }
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// type Config struct {
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// DefaultName string
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// DefaultAge int
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// }
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//
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// result := function.Pipe3(
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// reader.Do[Config](State{}),
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// reader.Bind(
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// func(name string) func(State) State {
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// return func(s State) State { s.Name = name; return s }
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// },
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// func(s State) reader.Reader[Config, string] {
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// return reader.Asks(func(c Config) string { return c.DefaultName })
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// },
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// ),
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// reader.Bind(
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// func(age int) func(State) State {
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// return func(s State) State { s.Age = age; return s }
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// },
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// func(s State) reader.Reader[Config, int] {
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// return reader.Asks(func(c Config) int { return c.DefaultAge })
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// },
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// ),
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// )
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func Do[R, S any](
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empty S,
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) Reader[R, S] {
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return Of[R](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 building up complex computations in a pipeline where each step can depend
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// on the results of previous steps and access the shared environment.
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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 { Value int }
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// type Config struct { Increment int }
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//
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// addIncrement := reader.Bind(
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// func(inc int) func(State) State {
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// return func(s State) State { return State{Value: s.Value + inc} }
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// },
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// func(s State) reader.Reader[Config, int] {
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// return reader.Asks(func(c Config) int { return c.Increment })
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// },
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// )
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func Bind[R, S1, S2, T any](
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setter func(T) func(S1) S2,
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f Kleisli[R, S1, T],
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) Operator[R, S1, S2] {
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return chain.Bind(
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Chain[R, S1, S2],
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Map[R, 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 pure computation to a context [S1] to produce a context [S2].
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// Unlike Bind, the computation function f does not return a Reader, just a plain value.
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// This is useful for transformations that don't need to access the environment.
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//
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// Example:
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//
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// type State struct {
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// FirstName string
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// LastName string
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// FullName string
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// }
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//
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// addFullName := reader.Let(
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// func(full string) func(State) State {
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// return func(s State) State { s.FullName = full; return s }
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// },
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// func(s State) string {
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// return s.FirstName + " " + s.LastName
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// },
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// )
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func Let[R, 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[R, S1, S2] {
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return functor.Let(
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Map[R, 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 a constant value to a context [S1] to produce a context [S2].
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// This is useful for adding fixed values to the context without any computation.
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//
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// Example:
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//
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// type State struct {
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// Name string
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// Version string
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// }
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//
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// addVersion := reader.LetTo(
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// func(v string) func(State) State {
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// return func(s State) State { s.Version = v; return s }
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// },
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// "1.0.0",
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// )
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func LetTo[R, 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[R, S1, S2] {
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return functor.LetTo(
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Map[R, 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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// This is typically used to start a binding chain by wrapping an initial Reader value
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// into a state structure.
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//
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// Example:
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//
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// type State struct { Name string }
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// type Config struct { DefaultName string }
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//
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// getName := reader.Asks(func(c Config) string { return c.DefaultName })
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// initState := reader.BindTo(func(name string) State {
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// return State{Name: name}
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// })
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// result := initState(getName)
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func BindTo[R, S1, T any](
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setter func(T) S1,
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) Operator[R, T, S1] {
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return chain.BindTo(
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Map[R, 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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//
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// This is useful when you have independent computations that can be combined without
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// one depending on the result of the other.
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//
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// Example:
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//
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// type State struct {
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// Host string
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// Port int
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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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// getPort := reader.Asks(func(c Config) int { return c.Port })
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// addPort := reader.ApS(
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// func(port int) func(State) State {
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// return func(s State) State { s.Port = port; return s }
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// },
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// getPort,
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// )
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func ApS[R, S1, S2, T any](
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setter func(T) func(S1) S2,
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fa Reader[R, T],
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) Operator[R, S1, S2] {
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return apply.ApS(
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Ap[S2, R, T],
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Map[R, 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 State struct {
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// Host string
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// Port int
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// }
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// type Config struct {
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// DefaultHost string
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// DefaultPort int
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// }
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//
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// portLens := lens.MakeLens(
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// func(s State) int { return s.Port },
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// func(s State, p int) State { s.Port = p; return s },
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// )
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//
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// getPort := reader.Asks(func(c Config) int { return c.DefaultPort })
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// result := F.Pipe2(
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// reader.Of[Config](State{Host: "localhost"}),
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// reader.ApSL(portLens, getPort),
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// )
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func ApSL[R, S, T any](
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lens L.Lens[S, T],
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fa Reader[R, T],
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) Operator[R, S, S] {
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return ApS(lens.Set, fa)
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}
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// BindL is a variant of Bind that uses a lens to focus on a specific part of the context.
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// This provides a more ergonomic API when working with nested structures, eliminating
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// the need to manually write setter functions.
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//
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// The lens parameter provides both a getter and setter for a field of type T within
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// the context S. The function f receives the current value of the focused field and
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// returns a Reader computation that produces an updated value.
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//
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// Example:
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//
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// type State struct {
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// Config ConfigData
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// Status string
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// }
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// type ConfigData struct {
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// Host string
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// Port int
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// }
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// type Env struct {
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// DefaultHost string
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// DefaultPort int
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// }
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//
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// configLens := lens.MakeLens(
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// func(s State) ConfigData { return s.Config },
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// func(s State, c ConfigData) State { s.Config = c; return s },
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// )
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//
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// result := F.Pipe2(
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// reader.Do[Env](State{}),
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// reader.BindL(configLens, func(cfg ConfigData) reader.Reader[Env, ConfigData] {
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// return reader.Asks(func(e Env) ConfigData {
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// return ConfigData{Host: e.DefaultHost, Port: e.DefaultPort}
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// })
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// }),
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// )
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func BindL[R, S, T any](
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lens L.Lens[S, T],
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f Kleisli[R, T, T],
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) Operator[R, S, S] {
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return Bind[R, S, S, T](lens.Set, F.Flow2(lens.Get, f))
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}
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// LetL is a variant of Let that uses a lens to focus on a specific part of the context.
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// This provides a more ergonomic API when working with nested structures, eliminating
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// the need to manually write setter functions.
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//
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// The lens parameter provides both a getter and setter for a field of type T within
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// the context S. The function f receives the current value of the focused field and
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// returns a new value (without wrapping in a Reader).
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//
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// Example:
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//
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// type State struct {
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// Config ConfigData
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// Status string
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// }
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// type ConfigData 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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// configLens := lens.MakeLens(
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// func(s State) ConfigData { return s.Config },
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// func(s State, c ConfigData) State { s.Config = c; return s },
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// )
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//
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// result := F.Pipe2(
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// reader.Do[any](State{Config: ConfigData{Host: "localhost"}}),
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// reader.LetL(configLens, func(cfg ConfigData) ConfigData {
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// cfg.Port = 8080
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// return cfg
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// }),
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// )
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func LetL[R, 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[R, S, S] {
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return Let[R, S, S, T](lens.Set, F.Flow2(lens.Get, f))
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}
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// LetToL is a variant of LetTo that uses a lens to focus on a specific part of the context.
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// This provides a more ergonomic API when working with nested structures, eliminating
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// the need to manually write setter functions.
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//
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// The lens parameter provides both a getter and setter for a field of type T within
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// the context S. The value b is set directly to the focused field.
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//
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// Example:
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//
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// type State struct {
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// Config ConfigData
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// Status string
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// }
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// type ConfigData 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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// configLens := lens.MakeLens(
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// func(s State) ConfigData { return s.Config },
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// func(s State, c ConfigData) State { s.Config = c; return s },
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// )
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//
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// newConfig := ConfigData{Host: "localhost", Port: 8080}
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// result := F.Pipe2(
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// reader.Do[any](State{}),
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// reader.LetToL(configLens, newConfig),
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// )
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func LetToL[R, S, T any](
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lens L.Lens[S, T],
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b T,
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) Operator[R, S, S] {
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return LetTo[R, S, S, T](lens.Set, b)
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}
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