Lisp Practice Exercises: Essential Techniques for Mastering the Framework

Here’s a short practice exercise to help you get more comfortable with Lisp programming:

Write a program in Lisp that takes a list of integers as input and outputs the sum of all the even numbers in the list.

Here’s a step-by-step guide to help you get started:

1. Define a function called “sum-even” using the “defun” keyword.
2. The function should take a single argument, which is a list of integers. You can use the “let” keyword to bind the input list to a variable.
3. Use the “loop” keyword to iterate over the list of integers. Use the “for” keyword to bind each element of the list to a variable.
4. Use the “when” keyword to check if the current element is even. If it is, add it to a running total.
5. Return the total as the output of the function.

Here’s an example implementation:

javaCopy code(defun sum-even (int-list)
  (let ((total 0))
    (loop for num in int-list
          when (evenp num)
          do (incf total num))
    total))

To use this function, you can call it with a list of integers as the input:

pythonCopy code(sum-even '(1 2 3 4 5 6))

This should output 12, which is the sum of the even numbers (2 + 4 + 6) in the input list.

By practicing exercises like this, you can start to build your skills in Lisp programming and become more comfortable with the unique syntax and features of this language.