Material to Understand

• mapcar

     (mapcar #'oddp '(1 2 3))         --> (t nil t)
  

• remove-if and remove-if-not

    (remove-if #'oddp '(1 2 3))       --> (2)
  
    (remove-if-not #'oddp '(1 2 3))   --> (1 3)
  

• count-if

    (count-if #'oddp '(1 2 3))        --> 2
  

• find-if

    (find-if #'oddp '(1 2 3))         --> 1
  

• funcall: function call

    (funcall #'append '(1 2) '(3 4))  --> (1 2 3 4)
  

• apply

    (apply #'append '((1 2) (3 4)))   --> (1 2 3 4)
  

• One time, anonymous functions using lambda. Lambda functions are most useful in the context of the mapping functions above.

  (mapcar #'(lambda (x) (+ x 1)) '(1 2 3))

Exercises

1. Write a recursive function called my-mapcar that produces the same results as mapcar, but does not use mapcar. For example, (my-mapcar #'oddp '(1 2 3)) should return (t nil t).
2. Write a recursive function called my-remove-if that produces the same results as remove-if. For example, (my-remove-if #'oddp '(1 2 3)) should return (2).
3. Write a recursive function called my-count-if that produces the same results as count-if. For example, (my-count-if #'oddp '(1 2 3)) should return 2.
4. Write a recursive function called my-find-if that produces the same results as find-if. For example, (my-find-if #'oddp '(1 2 3) should return 1.
5. Call my-find-if with a lambda function of your own choosing.
6. Explain the difference between funcall and apply.