Data Structures in Lisp 0. Collections of associations, association lists 1. Creating graphs with conses RPLACA and RPLACD (destructive editing) 2. Adjacency lists 3. Sequences 4. Arrays 5. Hash tables 6. Strings CSE 415 -- (c) S. Tanimoto, 2002 Lisp Data Structures

Collections of Associations A collection of associations can be thought of as a set, a function, or a many-many mapping. CONS is the fundamental mechanism for association in Lisp. An association list is a list of CONSes. However, for reasons of efficiency, there are alternatives to represent collections of associations in Lisp. (e.g., Hash tables) CSE 415 -- (c) S. Tanimoto, 2002 Lisp Data Structures

Direct Manipulation of Conses > (setq x (cons 'a 'b)) (A . B) > (rplaca x 'c) (C . B) > x > (rplacd x 'd) (C . D) > (rplacd x x) (C C C C C C C C C C ... ) > CSE 415 -- (c) S. Tanimoto, 2002 Lisp Data Structures

CSE 415 -- (c) S. Tanimoto, 2002 Lisp Data Structures Adjacency Lists Nowadays, RPLACA and RPLACD are less used. Straight lists are more common. Memory space is less of a concern. (setq nodes '(a b c d)) (setq arc-lists '( (a (b c)) (b (d)) (c (d)) (d ()) ) ) (defun is-edge (x y) (member y (second (assoc x arc-lists))) ) (is-edge 'a 'c) ; => (C) i.e., true. (is-edge 'a 'd) ; => NIL A C B D CSE 415 -- (c) S. Tanimoto, 2002 Lisp Data Structures

CSE 415 -- (c) S. Tanimoto, 2002 Lisp Data Structures Sequences A sequence can be thought of as a mapping from {0, 1, ..., n-1} to a set of range elements. A string is a sequence of characters. A list is a particular form of sequence of lisp objects. (typep "abc" 'sequence) ; => T. (typep '(a b c) 'sequence) ; => T. (concatenate 'string "abc" "def"); => "abcdef" (concatenate 'list '(a b) '(c d)); =>(a b c d) (elt '(a b c d) 2) ;=> C CSE 415 -- (c) S. Tanimoto, 2002 Lisp Data Structures

CSE 415 -- (c) S. Tanimoto, 2002 Lisp Data Structures Arrays An array is a mapping from a set of index tuples to a set of range elements. (setq a (make-array '(5 10):initial-element 1)) #2A((1 1 1 1 1 1 1 1 1 1) (1 1 1 1 1 1 1 1 1 1) (1 1 1 1 1 1 1 1 1 1)) (setf (aref a 4 9) 2) 2 (let ((sum 0)) (dotimes (i 5 sum)(dotimes (j 10) (incf sum (aref a i j)) )) ) 51 CSE 415 -- (c) S. Tanimoto, 2002 Lisp Data Structures

CSE 415 -- (c) S. Tanimoto, 2002 Lisp Data Structures Hashtables Association lists are linear and slow. For larger sets of associations, hashtables tend to be much faster. > (let ((h (make-hash-table))) (defun get-h (key) (gethash key h)) (defun put-h (key value) (setf (gethash key h) value)) ) PUT-H > (put-h 'x 'y) Y > (get-h 'x) Y ; The value associated with X T ; True, there is a value. > CSE 415 -- (c) S. Tanimoto, 2002 Lisp Data Structures

CSE 415 -- (c) S. Tanimoto, 2002 Lisp Data Structures MAPHASH ; Changes each entry in THE-HASH-TABLE, ; replacing each positive value with its ; square root, and removing negative values. (maphash ; Steele’84, p285. #'(lambda (key value) (if (minusp value) (remhash key the-hash-table) (setf (gethash key the-hash-table) (sqrt value)))) the-hash-table) ; returns NIL CSE 415 -- (c) S. Tanimoto, 2002 Lisp Data Structures

CSE 415 -- (c) S. Tanimoto, 2002 Lisp Data Structures Strings A Lisp string is written as a sequence of characters between double quotes. "This is a string." Double quotes can be entered using the backslash character "Here is a \"string within a string\"." Backslashes can be included by using a double backslash: "c:\\windows\\system\\temp.txt" A string is a one-dimensional array of characters. CSE 415 -- (c) S. Tanimoto, 2002 Lisp Data Structures

CSE 415 -- (c) S. Tanimoto, 2002 Lisp Data Structures Constructing Strings Concatenation > (concatenate 'string "Happy" " " "Birthday!") "Happy Birthday!" Character-by-character manipulation > (setq str (make-string 5 :initial-element #\A)) "AAAAA" > (setf (aref str 2 #\C)) #\C > str "AACAA" CSE 415 -- (c) S. Tanimoto, 2002 Lisp Data Structures

CSE 415 -- (c) S. Tanimoto, 2002 Lisp Data Structures Comparing Strings > (string= "happy" "happy") T > (string= "hapPy" "happy") NIL > (string/= "hapPy" "happy") 3 > (string-equal "hapPy" "happy") > (string-lessp "John" "johnny") 4 > (string< "John" "johnny") > (equal "hapPy" "happy") > (equalp "hapPy" "happy") CSE 415 -- (c) S. Tanimoto, 2002 Lisp Data Structures

String Input and Output > (setq line (read-line))This is a line of text. "This is a line of text." > (print line) > (format t "The input was: ~S" line) The input was: "This is a line of text." NIL > (format t "The input was: ~A" line) The input was: This is a line of text. > (setq line2 (format nil (format t "The input was: ~A" line))) "The input was: This is a line of text." CSE 415 -- (c) S. Tanimoto, 2002 Lisp Data Structures

CSE 415 -- (c) S. Tanimoto, 2002 Lisp Data Structures String Matching > (search "line" "This is a line of text.") 10 > (search "line" "THIS IS A LINE OF TEXT.") NIL > (search "line" "THIS IS A LINE OF TEXT." :test #'char-equal) > (search "xy9" "abcde01234" :key #'digit-char-p) 3 ; SEARCH works not only on strings but all sequences. > (search '(0 1) '(0 0 0 1 1 1)) 2 > (search '(0 1) '(2 4 8 7 5 3) :key #'evenp) CSE 415 -- (c) S. Tanimoto, 2002 Lisp Data Structures

CSE 415 -- (c) S. Tanimoto, 2002 Lisp Data Structures Substring Extraction > (subseq "This is a line of text." 10 14) "line" > (subseq "The remainder of the line." 4) "remainder of the line." > (setf (subseq "Let’s censor it." 6 12) "XYZXYZXYZW") "Let’s XYZXYZ it." CSE 415 -- (c) S. Tanimoto, 2002 Lisp Data Structures