Lua Function to Create a Local Function

This document provides a succinct implementation of a function in Lua that demonstrates how to define and invoke a local function.

Overview

• Purpose: To create a local function that performs a specific task, e.g., calculating the factorial of a number.
• Key Concepts: Local functions in Lua provide encapsulation and improve performance by limiting scope.

Implementation

Code

Here is the implementation of the function:

-- Function to calculate the factorial of a number using a local function
-- @param n (number): The number for which to calculate the factorial.
-- @return (number): The factorial of the input number.
-- @raises: an error if n is negative.

local function factorial(n)
    -- Validate input
    if n < 0 then
        error("Input must be a non-negative integer.")
    end
    
    -- Local helper function to calculate factorial recursively
    local function calculate(num)
        if num == 0 or num == 1 then
            return 1
        else
            return num * calculate(num - 1)
        end
    end
    
    return calculate(n) -- Call the local helper function
end

-- Example usage of the factorial function
local num = 5
local result = factorial(num) 
print("Factorial of " .. num .. " is: " .. result)

Explanation

1. Function Definition:

   • The factorial function takes one parameter n, which is the integer for which the factorial is to be computed.

2. Input Validation:

   • A check ensures that n is non-negative. If not, an error is raised.

3. Local Helper Function:

   • A local function calculate is defined to compute the factorial recursively.

4. Calling the Helper Function:

   • The helper function is invoked within the factorial function, and the result is returned.

5. Usage Example:

   • An example demonstrates how to call the factorial function and print the result for a given number.

Conclusion

This Lua function effectively demonstrates the creation of a local function for calculating factorials while adhering to robust input validation practices. Local functions are invaluable for maintaining cleaner code and reducing namespace pollution.

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