https://github.com/devstopfix/postfix-elixir

https://github.com/devstopfix/postfix-elixir

Last synced: 16 days ago
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• Host: GitHub
• URL: https://github.com/devstopfix/postfix-elixir
• Owner: devstopfix
• Created: 2022-11-27T11:00:58.000Z (almost 2 years ago)
• Default Branch: main
• Last Pushed: 2023-01-11T08:47:03.000Z (almost 2 years ago)
• Last Synced: 2024-09-30T08:17:05.818Z (about 1 month ago)
• Language: Elixir
• Size: 23.4 KB
• Stars: 0
• Watchers: 1
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

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README

        
# Postfix

Simple evaluator of a list of values and functions given in [postfix][postfix] order. 

```elixir

{:ok, 20} = Postfix.eval([7, 2, &-/2, 4, &*/2])

```

Inspired by [Factor][factor]. See [Postfix.Stack][stack] for examples.

[![Hex version badge](https://img.shields.io/hexpm/v/postfix.svg)](https://hex.pm/packages/postfix)

[![ci](https://github.com/devstopfix/postfix-elixir/actions/workflows/ci.yml/badge.svg?branch=main)](https://github.com/devstopfix/postfix-elixir/actions/workflows/ci.yml)

## Usage

Functions are evaluated with all the operands to their left, and the result

replaces the function it's operands in the list and evaluation continues.

If any function returns an `{:ok, value}` tuple then the value is unwrapped

and used as the result.

Any function that fails with an `{:error, _}` tuple short-circuits and 

becomes the result of the evaluation.

There are two implementations:

* `Postfix.Simple` for simple pipelines using a list

* [Postfix.Stack][stack] which uses a list for the program and a stack for operands and results

### Limitations

It is not possible to pass a function to a higher-order function as it will be evaluated.

Given the filter example:

```elixir

is_odd? = fn x -> rem(x, 2) == 0 end

Enum.filter(1..3, is_odd?)

```

This *cannot* be written as:

```elixir

is_odd? = fn x -> rem(x, 2) == 0 end

{:ok, [2]} = Postfix.eval([1..3, is_odd?, &Enum.filter/2])

```

However it could be written as:

```elixir

is_odd? = fn x -> rem(x, 2) == 0 end

filter_odd = fn xs -> Enum.filter(xs, is_odd?) end

{:ok, [2]} = Postfix.eval([1..3, filter_odd])

```

## Installation

This package can be installed

by adding `postfix` to your list of dependencies in `mix.exs`:

```elixir

def deps do

  [

    {:postfix, "~> 1.2"}

  ]

end

```

## License

Copyright 2022 J Every

Released under the [MIT License][mit]

[factor]: https://factorcode.org/

[mit]: https://opensource.org/licenses/MIT

[postfix]: https://en.wikipedia.org/wiki/Reverse_Polish_notation

[stack]: https://hexdocs.pm/postfix/Postfix.Stack.html