Proc composition in Ruby - Mini Project: Build & Apply

Proc composition

📖 Scenario: You are working on a small Ruby program that processes numbers using reusable pieces of code called Procs. Procs are like little machines that take input and give output. You want to combine these machines to create a new machine that does two things in order.

🎯 Goal: Build a Ruby program that creates two simple Procs, then combines them into one Proc that applies both steps in sequence. Finally, run the combined Proc on a number and see the result.

📋 What You'll Learn

Create two Procs named double and increment.

double should multiply its input by 2.

increment should add 1 to its input.

Create a new Proc called double_then_increment that applies double first, then increment.

Call double_then_increment with the number 3 and print the result.

💡 Why This Matters

🌍 Real World

Proc composition is useful when you want to build complex operations from simple reusable steps, like processing data or applying filters.

💼 Career

Understanding Proc composition helps in writing clean, modular Ruby code often used in web development and scripting tasks.

1

Create two Procs

Create a Proc called double that multiplies its input by 2, and another Proc called increment that adds 1 to its input.

Ruby

# Create the Proc double and increment here
# Your code here

Need a hint?

Use Proc.new { |x| ... } to create each Proc.

2

Create a composed Proc

Create a new Proc called double_then_increment that takes one argument x, applies double to x, then applies increment to the result.

Ruby

double = Proc.new { |x| x * 2 }
increment = Proc.new { |x| x + 1 }
# Create double_then_increment Proc here
# Your code here

Need a hint?

Inside the new Proc, call double.call(x) first, then pass that result to increment.call(...).

3

Call the composed Proc

Call the Proc double_then_increment with the number 3 and store the result in a variable called result.

Ruby

double = Proc.new { |x| x * 2 }
increment = Proc.new { |x| x + 1 }
double_then_increment = Proc.new { |x| increment.call(double.call(x)) }
# Call double_then_increment with 3 and save to result
# Your code here

Need a hint?

Use double_then_increment.call(3) and assign it to result.

4

Print the result

Print the value of the variable result.

Ruby

double = Proc.new { |x| x * 2 }
increment = Proc.new { |x| x + 1 }
double_then_increment = Proc.new { |x| increment.call(double.call(x)) }
result = double_then_increment.call(3)
# Print the result
# Your code here

Need a hint?

Use puts result to display the output.