LISP 113
November 11th, 2021 EL Notes Guest on 23rd November 2021 06:47:24 AM
  1. ;;pick function will return the nth element in the list l.
  2. (defun pick (n l)
  3.   ( cond
  4.     ( (null l) l)
  5.     ( (eq n 1) (car l))
  6.     ( t ( pick (- n 1) (cdr l)))
  7.   )
  8.  )
  9.  
  10. ;pick demo
  11. (pick 1 '(4 5 6))
  12. ; 4
  13. (pick 4 '(4 5 6))
  14. ;nil
  15.  
  16.  
  17. ;;leftmost function will return the leftmost atom in a given list l.
  18. (defun leftmost (l)
  19.   ( cond
  20.     ( (null l) l)
  21.     ( (atom (car l)) (car l))
  22.     ( t (leftmost (car l)))
  23.   )
  24. )
  25.  
  26. ;leftmost demo
  27. (leftmost '(4 5 6))
  28. ; 4
  29. (leftmost '( (4 5) 6 (3 4)))
  30. ; 4
  31. (leftmost '( ( (2 3) 4) 5 (6 7)))
  32. ; 2
  33. (leftmost '( ( (4) 5) 6 (3 4)))
  34. ; 4
  35.  
  36. ;;car cdr car == cadar
  37. ;;cdr cdr car == cddar
  38.  
  39. (cdr (car (cdr '(9 (3 5) (7 5 (3 4))) ) ) )
  40. ; 5
  41.  
  42. (cdadr '(9 (3 5) (7 5 (3 4))))
  43. ; 5
  44.  
  45. (caadr '( (2 3) (1 2) (5 6 7)))
  46. ; 1
  47.  
  48. (car (car (cdr '((2 3) (1 2) (5 6 7)))))
  49. ; 1
  50.  
  51.  
  52. ;; declare x = 2
  53. (set 'x 2)
  54.  
  55. x
  56. ; 2
  57.  
  58.  
  59. ;; set + quote so you don't need to put the quote before y
  60. (setq y 3)
  61. y
  62. ; 3
  63.  
  64. (+ x y)
  65. ; 5
  66. (* x y)
  67. ; 6
  68.  
  69. ;;you can find a car/cdr of a generated list
  70. (car (list 3 4 'a 'b 6))
  71. ; 3
  72.  
  73. ;;condition with manipulation
  74. ( cond
  75.   ( (> x 5) (+ x 1))
  76.   ( t (- x 1))
  77.   )
  78. ; 1
  79.  
  80. ;;conditions and or not
  81. (if (> x 5) (+ x 1) (- x 1))
  82. ; 1
  83. (if (not (or (> x 5) (< x 0))) (+ x 1) (- x 1))
  84. ; 3
  85. ;same as before with cond
  86.  
  87.  
  88. ;; display maximum item of list
  89. (max 3 5)
  90. ; 5
  91.  
  92. ;; apply operator
  93. (apply '+ '(3 4 5))
  94. ; 12
  95.  
  96.  
  97. ;;you can substitute ' with quote
  98. (setq op '*)
  99. ; *
  100.  
  101. ;;substitute our variable op for *
  102. (apply op '(3 4 5))
  103. ; 60
  104.  
  105. ;;same but with max
  106. (setq op2 'max)
  107. ; max
  108. (apply op2 '(3 4 5))
  109. ; 5
  110. (apply op2 '(4 7 3))
  111. ; 7
  112.  
  113. ;; returns true if is a number
  114. (numberp 4)
  115. ; t
  116.  
  117. (numberp 'a)
  118.  
  119.  
  120. (numberp '(3 4))
  121. ; nil
  122.  
  123. (numberp 100)
  124. ; t
  125.  
  126.  
  127. ;;returns items in list that aren't numbers
  128. (defun no-num (l)
  129.   ( cond
  130.     ( (null l) l)
  131.     ( (numberp (car l)) (no-num (cdr l)))
  132.     ( t (cons (car l) (no-num (cdr l))))
  133.     )
  134.   )
  135.  
  136.  
  137. (no-num '(1 'a 'b 3 'flower))
  138. ; ('a 'b 'flower)
  139.  
  140. (no-num '(3 5 6))
  141. ; nil
  142.  
  143. x
  144. ; 2
  145. y
  146. ; 3
  147. (no-num '(a b c x y))
  148. ; (a b c x y)
  149. (no-num '(5 'a 'b 'flower 100 15 'car))
  150. ; ('a 'b 'flower 'car)

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