https://github.com/kiaragrouwstra/elins

lenses for elixir
https://github.com/kiaragrouwstra/elins

Last synced: about 1 month ago
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lenses for elixir

• Host: GitHub
• URL: https://github.com/kiaragrouwstra/elins
• Owner: KiaraGrouwstra
• Created: 2015-10-16T12:03:02.000Z (about 9 years ago)
• Default Branch: master
• Last Pushed: 2016-02-25T13:39:14.000Z (almost 9 years ago)
• Last Synced: 2024-10-15T13:31:03.311Z (3 months ago)
• Language: Elixir
• Size: 12.7 KB
• Stars: 6
• Watchers: 2
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

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README

        
# Lenses in Elixir

## Usage:

```elixir

import Elins

# make a kitten to alter

kitten = %{name: "Mr. Bigglesworth", color: %{r: 1.0, g: 1.0, b: 1.0}}

# make a new kitten with a (deep) property set to a new value

kitten |> set([:color, :b], 0.0).()

# result: new kitten with 0 blue

# make a new kitten with a (deep) property changed

kitten |> edit([:color, :g], fn(v) -> 0.5 * v end).()

# result: new kitten with green halved

# set multiple properties (deep merge)

kitten |> setVals(%{ name: "Garfield", color: %{ r: 0.5 } }).()

# result: new kitten with name and red color changed

# make a new kitten with multiple properties changed by function

kitten |> editVals(%{ name: &String.upcase/1, color: %{ r: &(0.5 * &1) } }).()

# result: new kitten with name upcase'd and red halved

# make a new kitten with multiple properties changed through maps and lists

%{name: "Mr. Bigglesworth", children: [ %{num: 1}, %{num: 2}, %{num: 3} ] } |>

editVals(%{ name: &String.upcase/1, children: [ %{ num: &(&1 + 1) } ] }).()

# result: new kitten with name upcase'd and each child number incremented

# properties can even derive from other properties

total = fn(_x, cat) ->

  clr = cat.color

  clr.r + clr.g + clr.b

end

kitten |> editVals(%{

  age: fn(_x, cat) -> cat.name |> String.length() end,

  color: %{ r: total, g: total, b: total }

}).()

# result: %{name: "Mr. Bigglesworth", age: 16, color: %{r: 3.0, g: 5.0, b: 9.0}}

# note that since color properties on kitten were defined in order r -> g -> b,

# the alterations are triggered in the same order. hence blue gets more here.

```

Beside `Map`s these work on [`Structs`](http://elixir-lang.org/getting-started/structs.html) as well (which essentially are `Map`s anyway).

This started as a minimal Elixir port of @jlouis's [erl-lenses](https://github.com/jlouis/erl-lenses), which was to be superseded by his [forge](https://github.com/jlouis/forge), but expanded from there to expose this friendlier interface.

* Q: how about chaining multiple functions?

* A: [compose](https://github.com/tycho01/fun) them.

* Q: Why the ugly `.()`? :(

* A: It ends up nicer for iteration; you could do say `my_kittens |> Enum.map(setVals(%{ ... }))` to have the lens initialize once then get used for each item in your list.