Proc composition in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a Proc in Ruby?

A Proc is an object that holds a block of code which can be stored in a variable and called later. It allows you to treat code as data.

beginner

How do you create a Proc in Ruby?

You can create a Proc using Proc.new { |args| ... } or the shorthand proc { |args| ... }.

intermediate

What does Proc composition mean?

Proc composition means combining two or more Procs so that the output of one becomes the input of another, creating a chain of operations.

intermediate

How can you compose two Procs in Ruby?

You can compose two Procs by creating a new Proc that calls the second Proc and then passes its result to the first Proc.

intermediate

Example: Compose Proc p1 = proc { |x| x + 2 } and p2 = proc { |x| x * 3 }. What is the result of calling the composition with 4?

The composition applies p1 first: 4 + 2 = 6, then p2: 6 * 3 = 18. So the result is 18.

What is the main purpose of a Proc in Ruby?

A To create a variable

B To store a block of code for later use

C To define a class

D To handle exceptions

A Proc stores a block of code that can be called later.

How do you call a Proc stored in variable p?

A execute(p)

B call(p)

C p()

D p.call()

You call a Proc by using the call method on it.

In Proc composition, what happens to the output of the first Proc?

A It becomes input to the next Proc

B It is ignored

C It is printed automatically

D It resets the program

The output of the first Proc is passed as input to the next Proc in the composition.

Given p1 = proc { |x| x * 2 } and p2 = proc { |x| x + 3 }, what is the result of composing p2 after p1 and calling with 5?

A 10

B 16

C 13

D 8

First p1: 5 * 2 = 10, then p2: 10 + 3 = 13.

Which Ruby method is used to create a Proc?

A Proc.new

B def

C lambda

D class

Proc.new creates a Proc object.

Explain what Proc composition is and how it works in Ruby.

Think about how you can connect small steps to make a bigger step.

Write a simple Ruby example that composes two Procs and explain the result.

Use simple math operations like addition and multiplication.