https://github.com/414owen/multi-except

Haskell Applicative Exception type that supports multiple exceptions reported by one computation
https://github.com/414owen/multi-except

applicative haskell

Last synced: 5 months ago
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Haskell Applicative Exception type that supports multiple exceptions reported by one computation

• Host: GitHub
• URL: https://github.com/414owen/multi-except
• Owner: 414owen
• License: mit
• Created: 2021-05-11T16:02:07.000Z (over 4 years ago)
• Default Branch: master
• Last Pushed: 2024-04-16T15:44:03.000Z (almost 2 years ago)
• Last Synced: 2025-08-22T13:06:22.786Z (5 months ago)
• Topics: applicative, haskell
• Language: Haskell
• Homepage:
• Size: 122 KB
• Stars: 1
• Watchers: 2
• Forks: 1
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • Changelog: CHANGELOG.md
  • License: LICENSE

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README

          
# multi-except

[![Hackage version](https://img.shields.io/hackage/v/multi-except?color=purple)](https://hackage.haskell.org/package/multi-except)

[![CI Status](https://img.shields.io/github/actions/workflow/status/414owen/multi-except/haskell-ci.yml)](https://github.com/414owen/multi-except/actions)

[![GitHub License](https://img.shields.io/github/license/414owen/multi-except)](https://github.com/414owen/multi-except/blob/master/LICENSE)

multi-except - succeed, or return one or more errors

## Adding the dependency

```

-- in your cabal file

  -- Add the main package (only depends on base!)

  , multi-except

  -- For the Alt instance (depends on semigroupoids)

  , multi-except:semigroupoid-instances

```

## Usage

```haskell

{-# LANGUAGE ApplicativeDo #-}

import Control.Applicative.MultiExcept

errors :: MultiExcept String (Int, Int, Int)

errors = do

  a <- throwError "no monad instance"

  b <- pure 12

  c <- throwError "i am scared"

  pure (a, b, c)

-- errors: Errors ["no monad instance", "i am scared"]

```

The use of `ApplicativeDo` is significant and necessary for using

`MultiExcept` with do notation.

`MultiExcept` is not a `Monad`, only an `Applicative`, so a few constraints

apply, such as not being able to determine the structure of the rest of the

computation based on a previously do-bound value. If the previous sentence was

confusing, then you might want to consider using a writer monad instead.

To compose with other applicative effects, you can use

[`Data.Functor.Compose`](https://hackage.haskell.org/package/base-4.19.0.0/docs/Data-Functor-Compose.html).