# tuple-classes

[![Hackage](https://img.shields.io/hackage/v/tuple-classes)](https://hackage.haskell.org/package/tuple-classes)

Haskell facilities for manipulating _n_-ary tuples and functions.
  * ❨Generalized uncurrying and un-uncurrying❩
  * ❨Inserting and removing fields❩
  * ❨van Laarhoven optics ❟ courtesy microlens❩
    * ❨Build with flag `tuple-classes:lens` for `Iso`s instead❩
  * ❨Designed to complement the popular [strict](https://hackage.haskell.org/package/strict) package❩
  * ❨`StrictTuple3` ❟ `StrictTuple4` ❟ ... up to `StrictTuple9` provided❩
  * ❨More instances than you can shake a stick at❩
    * ❨`Strict`❩
    * ❨`Each` ❨`each`❩ and `Field1` ❨`_1`❩ ❟ `Field2` ❨`_2`❩ ❟ etc.❩
  * ❨Pragmatic re-exports❩

```haskell
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE TypeApplications #-}

import Data.Tuple.Classes (uncurriedN')
import Lens.Micro         (over)

-- Function wrapper that expects a unary function
printArgAndRun :: (Show a) => (a -> IO b) -> a -> IO b
printArgAndRun f x = do
    print x
    f x

-- But we have a ternary function
printTitleAndSum :: String -> Int -> Int -> IO ()
printTitleAndSum title i j = do
    putStrLn title
    print $ i + j

-- We can adapt it
printArgsTitleAndSum :: String -> Int -> Int -> IO ()
printArgsTitleAndSum = over (uncurriedN' @3) printArgAndRun printTitleAndSum

main :: IO ()
main = printArgsTitleAndSum "Important identity" 26885 15184
```

```
StrictTuple3 "Important identity" 26885 15184
Important identity
42069
```

```haskell
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE TypeApplications #-}

import Data.Tuple.Classes (TupleAt(..))

consTuple :: (TupleAt 1 a t u) => a -> t -> u
consTuple = tupleInsert @1
infixr `consTuple`

main :: IO ()
main = print $ 'x' `consTuple` False `consTuple` ("sequitur", "quodlibet")
```

```
('x',False,"sequitur","quodlibet")
```

## Prior art

* Edward Kmett's lens's [`Field1` etc.](https://hackage-content.haskell.org/package/lens-5.3.6/docs/Control-Lens-Tuple.html) and [`Each`](https://hackage-content.haskell.org/package/lens-5.3.6/docs/Control-Lens-Each.html#t:Each)
* Lennart Augustsson's [`Curry`](https://hackage.haskell.org/package/tuple-0.3.0.2/docs/Data-Tuple-Curry.html) class
* Mitchell Rosen's [strict-tuple](https://hackage.haskell.org/package/strict-tuple-0.1.5.4/docs/Data-Tuple-Strict.html) which unfortunately would need some unnecessary-looking breaking changes to suit this library:
  * Removing `Biapplicative` instances in order to not depend on the heavy bifunctors package
  * Removing `T1` and `T2` which conflict with the much more supported `Identity` and `Pair`
* [mangoiv's proof-of-concept](https://bin.mangoiv.com/note?id=d204d07f-6292-4eb7-9aff-4cabc78394b9) related to keyword args and arbitrary function arity

Credit to mango for suggesting the limitations of that approach and indirectly shaping this library's design.

## LLM contribution policy

https://en.wikipedia.org/wiki/TESCREAL

## License

[Apache 2.0](https://www.apache.org/licenses/LICENSE-2.0.html)

## Main Author

©2026 Steven Shuck