Funx.Monad.Effect.Left

Mix.install([
  {:funx,
    git: "https://github.com/JKWA/funx.git",
    branch: "main"
  }
])

Overview

Represents the Left variant of the Effect monad, used to model a failure or error in an asynchronous context.

This module implements the following protocols:

• Funx.Monad: Implements bind/2, map/2, and ap/2 for monadic sequencing in a lazy, effectful context.
• String.Chars: Provides a string representation of the effect for debugging and inspection.

A Left effect propagates its failure value without invoking further computations, preserving short-circuit behavior.

Reader Operations

• ask/1 – Returns the environment passed to run/2 as a Left.
• asks/2 – Applies a function to the environment passed to run/2, wrapping the result in a Left.

Function Examples

import Funx.Monad.Effect.Left
alias Funx.Monad.Effect.Left

Functions

pure/2

Creates a new Left effect.

Wraps a failure value in an asynchronous effect. You may provide context either as a keyword list or an Effect.Context struct.

Examples

effect = pure("error")
Funx.Monad.Effect.run(effect)

ask/1

Returns a Funx.Monad.Effect.Left that yields the environment passed to Funx.Monad.Effect.run/2.

This is the Reader-style ask, used to construct a failure from the full injected environment. It can be useful for debugging, instrumentation, or propagating request-scoped failure information.

Example

ask()
|> Funx.Monad.Effect.run(%{error: :unauthorized})

asks/2

Returns a Funx.Monad.Effect.Left that applies the given function to the environment passed to Funx.Monad.Effect.run/2.

This allows constructing a failure (Left) based on runtime input. It complements Right.asks/2, but marks the result as a failure rather than a success.

Example

asks(fn env -> {:error, env[:reason]} end)
|> Funx.Monad.Effect.run(%{reason: :invalid})