LISP 101
November 4th, 2021 EL Notes Guest on 23rd November 2021 04:00:38 AM
  1. ;;simple list contains atoms
  2. '(1 2 3)
  3. ; (1 2 3)
  4.  
  5. ;;substitute ' for the word quote
  6. (quote (1 2 3))
  7. ; (1 2 3)
  8.  
  9. ;;atoms can be letters too
  10. '(a b c)
  11. ; (a b c)
  12.  
  13. ;;atom returns true if something is an atom
  14. (atom 2)
  15. ; t
  16.  
  17. ;;check if is an atom?? or apply atom to a
  18. (atom 'a)
  19. ; t
  20.  
  21. ;;atom returns false for a list
  22. (atom '(3 4 5))
  23. ; nil
  24.  
  25. (atom '(atom 'a))
  26. ; nil
  27.  
  28. (atom (atom 'a))
  29. ; t
  30.  
  31. (atom (atom '(3 4 5)))
  32. ; t
  33.  
  34. ; nil
  35.  
  36.  
  37. (atom nil)
  38. ; t
  39.  
  40.  
  41. ;;comparisons
  42.  
  43. ;;compare undefined variables
  44. (eq 'a 'b)
  45. ; nil
  46.  
  47. ;;compare avlues
  48. (eq 1 1)
  49. ; t
  50.  
  51. ; comparison of lists will not return true (see eqlist function below)
  52. (eq '(2 3) '(2 3))
  53. ; nil
  54.  
  55.  
  56. ;;car = head of list
  57. ;;cdr = tail of list
  58.  
  59. (car '(4 5 6))
  60. ; 4
  61.  
  62. (cdr '(5 6 7))
  63. ; (6 7)
  64.  
  65. (cdr '( (2 3) (1 2) (5 6 7)))
  66. ; ((1 2) (5 6 7))
  67.  
  68.  
  69. ;;construct list from lists
  70. (cons  '2 '(3 4 5))
  71. ; (2 3 4 5)
  72.  
  73. (cons '(1 2) '(3 4 5))
  74. ; ((1 2)
  75.  
  76. ;; conditional statements
  77. (cond
  78.  ( (eq 'a 'b) '3)
  79.  ((eq '2 '2) '4))
  80. ; 4
  81. ;;returns 4 because a doesn't equal b, but 2 does equal 2
  82. ;;if a equalled b then it would return 3
  83.  
  84. ;;define a function = defun
  85. ;;function that doubles
  86. (defun double (x)
  87.   (* 2 x))
  88.  
  89. (double 3)
  90. ; 6
  91.  
  92.  
  93. ;;returns true if null, false if not null
  94. (null '())
  95. ; t
  96.  
  97. (null '(1))
  98. ; nil
  99.  
  100. ;;list of atoms function
  101. (defun lat (l)
  102.   (cond
  103.    ((null l) t)
  104.    ((atom (car l)) (lat(cdr l)))
  105.    (t nil)
  106.    )
  107.   )
  108.  
  109. (lat '(1 3 3 4))
  110. ; t
  111.      
  112. (lat '(1 (2 3) 4))
  113. ; nil
  114.  
  115. ;;and returns true if everything is true
  116. (and (atom 2) (atom 'a))
  117. ; t
  118.  
  119.  
  120. ;;eqlist function will return true for list of atoms comparisons recursively
  121. (defun eqlist (l1 l2)
  122.   (cond
  123.    ( (and (null l1) (null l2)) t)
  124.    ( (eq (car l1) (car l2)) (eqlist (cdr l1) (cdr l2)))
  125.    (t nil)
  126.    )
  127.   )
  128.  
  129. (eqlist '(1 2 3 4 5) '(1 2 3 4 5))
  130. ; t
  131.  
  132. ;;will return if an atom exists in a list
  133. (defun member2 (x l)
  134.   (cond
  135.    ( (null l) nil)
  136.    ( (eq x (car l)) t)
  137.    ( t (member2 x (cdr l)))
  138.    )
  139.   )
  140.  
  141. (member2 '6 '(1 2 3 4 5))
  142. ; nil
  143.  
  144. (member2 '6 '(2 6 8))
  145. ; t
  146.  
  147. ;;not will invert true/nil statements
  148. (not (eq 2 2))
  149. ;nil
  150.  
  151. (not (eq 1 2))
  152. ;t
  153.  
  154. ;;list of non-atoms, aka list of lists
  155. (defun nonlat (l)
  156.   (cond
  157.    ( (null l) t)
  158.    ( (not (atom (car l))) (nonlat (cdr l)))
  159.    ( t nil)
  160.    )
  161.   )
  162.  
  163. (nonlat '(1 2 3))
  164. ; nil
  165.  
  166. (nonlat '((2 3) 4 5 (5)))
  167. ; nil
  168.  
  169. (nonlat '((2 3) (2 4)))
  170. ; t

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