composition

It's functions all the way down: Composition

In functional programming we construct programs entirely out of modular pure functions, using function composition to "combine" functions' effects to create a pipeline through which our program's data can flow through.

Exercises

Pipelining (pipeline.js)

• Run the tests in pipeline.test.js with the command node pipeline.test.js - tests should be failing
• Get the tests to pass by implementing the pipeline function, which takes as arguments any number of single-argument functions and returns a single function representing their composition, i.e. a function that passes the input value through a "pipeline" of the functions.
  • [challenge] Implement the pipeline function in one line, using the reduce function you implemented in higher-order/filterMapReduce.js
• Compare your implementation(s) with those of your partner/group

The case for composition (snakeCharmer.js)

• Run the tests in snakeCharmer.test.js with the command node snakeCharmer.test.js - tests should be failing, let's get them to pass
• Fill in the snakeToCamel function to make a composed function that reformats a string from snake_case to camelCase. Try to break down the transformation into small functions, then use your pipeline function to compose them.
• Fill in the snakeToTrain function to reformat a string from snake_case to Train-Case. How much of your code from snakeToCamel can you reuse?
• [challenge] Write more functions to translate to more cases, e.g. PascalCase, kebab-case, SCREAMING_SNAKE_CASE, SCREAMING-TRAIN-CASE, etc... - try to use pipelining to reuse as much code as possible!
• [challenge] Since our pipeline operates on single-argument functions, it will work great in combination with currying. Try to de-clutter your snakeCharmer code by writing & using curried versions of the filter, map, and reduce functions - in what cases does currying help?