Pipet

A library for conditionally chaining data through a series of operations

Installation

Add pipet to your list of dependencies in mix.exs.

def deps do
  [
    {:pipet, "~> 0.1.0"}
  ]
end

Documentation can be found here.

Elixir's |> (pipe) operator is one of its best features; it mixes extremely well with a functional, immutable style of programming. It tends to break down, however, when you want to perform the operations in a pipeline only sometimes, for instance in response to an options keyword passed to your function. How many times have you wanted to perform something in a pipeline conditionally, but instead had to write something like the following:

def get_names(people, options \\ []) do
  results =
    people
    |> Stream.map(fn %Person{name: name} -> name end)

  results =
    if Keyword.fetch(options, :upcase) do
      people
      |> Stream.map(&String.upcase/1)
    else
      people
    end

  Enum.to_list(results)
end

Pipet provides a single macro, pipet, which extends the semantics of piping to function properly with all of elixir's built-in conditional expressions in a simple, clean, and obvious way. The code sample above could be rewritten with pipet like this:

import Pipet

def get_names(people, options \\ []) do
  pipet people do
    Stream.map(fn %Person{name: name} -> name end)

    if Keyword.fetch(options, :upcasee) do
      Stream.map(&String.upcase/1)
    end

    Enum.to_list()
  end
end

Way cleaner! No variable rebinding, no pointless else block for the if statement, just the code that matters.

Pipet works with all of Elixir's built-in conditional operators in addition to just if. All the following should work exactly as you expect them to:

• if
• unless
• case
• cond

Prior Art

Pipet originally started as a port of the Clojure standard library's cond-> macro, before very quickly outgrowing the feature set of that macro into something that very closely resembles packthread, also for Clojure. Acknowledgements go to @richhickey for the former and @eraserhd for the latter.

License

Copyright 2017 Urbint

Licensed under the MIT License

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.