Pipe

OSAAT1.md

Scalaz: one symbol at a time (OSAAT#1)

Symbol

|> or ▹

Pronounced

• Pipe
• The Thrush combinator

Purpose

• Improved readability for a pipeline of functions.
• Use where the value of one function is fed as an input to the next function.
• Analogous to the UNIX pipe operator (|).

##Example

Instead of...

nearby(extractLocations(tweets))

... you can pipe these functions together:

import scalaz.syntax.id._

tweets |> extractLocations |> nearby

where:

• tweets is a value;
• the type of that value is expected as a parameter to extractLocations; and
• the result of extractLocations is the input to the nearby function.

Alternatives

Working with an alternative API, using maps and predicates, you might write:

tweets.flatMap(findLocation).filter(isNearby)

Fun fact

The name "thrush" originates in Raymond Smullyan's To Mock a Mockingbird (and other logic puzzles). From page 100:

"A bird closely related to the cardinal is the thrush," said Bravura. "Why, there is one right over there! A thrush T is defined by the following condition:

Txy = yx

"The thrush is the simplest of the permuting birds," said Bravura. "It is derivable from a cardinal C and an identity bird I. Can you see how?"