;;;; Section 1.7 ;;;;
;Adam Nelson
;Chet Tobrey

(defun mappend (fn the-list)
  "Apply fn to each element of list and append the results."
  (apply #'append (mapcar fn the-list)))

(defun self-and-double (x) (list x (+ x x)))

(defun number-and-negation (x)
  "If x is a number, return a list of x and -x."
  (if (numberp x)
      (list x (- x))
      nil))

(defun numbers-and-negations (input)
  "Given a list, return only their numbers and negations"
  (mappend #'number-and-negation input))

(defun mappend2 (fn the-list)
  "Apply fn to each element of list and append the results"
  (if (null the-list)
      nil
     (append (funcall fn (first the-list))
              (mappend2 fn (rest the-list)))))

 

(egs :1.7
     (eg '(apply #'+ '(1 2 3 4))
         :of "Applies the addition function to a list of four numbers"
         :out '10)
     (eg '(apply #'append '((1 2 3) (a b c)))
         :of "Applies append to the two lists 123 and abc"
         :out '(1 2 3 a b c))
     (eg '(self-and-double 3)
         :of "Calls self-and-double with parameter 3"
         :out '(3 6))
     (eg '(apply #'self-and-double '(3))
         :of "Applies self-and-double and the parameter 3"
         :out '(3 6))
     (eg '(mapcar #'self-and-double '(1 10 300))
         :of "Uses mapcar with the self-and-double function"
         :out '((1 2) (10 20) (300 600)))
     (eg '(mappend #'self-and-double '(1 10 300))
         :of "Uses the self-and-double function with the mappend function - same as above but appends results"
         :out '(1 2 10 20 300 600))
     (eg '(numbers-and-negations '(testing 1 2 3 test))
         :of "Testing the numbers and negations function"
         :out '(1 -1 2 -2 3 -3))
     (eg '(funcall #'+ 2 3)
         :of "Using funcall to add two numbers"
         :out '5)
     (eg '(apply #'+ '(2 3))
         :of "Using apply to add two numbers"
         :out '5)
     (eg '(funcall #'(lambda (x) (+ x 2)) 4)
         :of "Tests the funcall function with a lambda function"
         :out '6)
     (eg '(mapcar #'(lambda (x) (+ x x)) '(1 2 3 4 5))
         :of "Uses mapcar with a lambda function"
         :out '(2 4 6 8 10))
     (eg '(mappend2 #'(lambda (l) (list l (reverse l))) '((1 2 3) (a b c)))
         :of "Uses mappend with a lambda function and reverses the lists as inputs"
         :out '((1 2 3) (3 2 1) (a b c) (c b a))) )