CMSC 471 LISP

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CMSC 471LISP
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Comic from xkcd.com
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Why Lisp?

• Because its good for writing production software
• Because its got lots of features other languages
  dont
• Because you can write new programs and extend old
  programs really, really quickly in Lisp

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Great! How can I get started?

• On sunserver (CS) and gl machines, run
  /usr/local/bin/clisp
• From http//clisp.cons.org you can download CLISP
  for your own PC (Windows or Linux)
• Great Lisp resource page http//www.apl.jhu.edu/
  hall/lisp.html

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Basic Lisp

• Surprisingly readable if you indent properly
  (dont use a plain text editor)
• Lisp syntax parenthesized prefix notation
• Lisp interpreter read-eval-print loop
• ( 1 2)
• ( ( 1 2) 3)
• (list ( 3 5) atom (list inside a list) (list 3
  4) (((very) (very) (very) (nested list))))

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Basic Lisp types

• Numbers (integers, floating-point, complex)
• 27 -2 7.519
• Characters, strings (arrays of chars)
• \x \- \B
• This is a string!
• Symbols
• a x jon
• Lists (linked cells)
• Empty list nil
• (a b c) (2 3 jon)
• cons structure has car (first) and cdr (rest)

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Built-in functions

• For numbers
• - / incf() decf(--)
• A diversion destructive functions
• (setf x 1)
• (setf y ( x 1)) vs. (setf y (incf x))
• For lists
• car (first) cdr (rest) second third fourth
• length nth
• cons append(list concatenation) nconc list
• mapcar mapcan
• find remove remove-if

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Built-in functions (contd)

• Printing print, format
• (print string) ? print output
• (format ) ? formatted output
• Advanced list processing assoc, mapcar
• Predicates listp, numberp, stringp, atom, null,
  equal, eql, and, or, not
• Special forms setq/setf, quote, defun,
  defparameter, defconstant, if, cond, case, progn,
  loop

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More Lisp types

• Arrays (with zero or more dimensions)
• Hash tables
• Streams (for reading and writing)
• Structures
• Functions, including lambda functions
• (defun incBy10 (n) ( n 10))
• (mapcar (lambda (n) ( n 10))
• (1 2 3 4 5))

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Useful help facilities

• (apropos str) ? list of symbols whose name
  contains str
• (describe symbol) ? description of symbol
• (describe fn) ? description of function
• (trace fn) ? print a trace of fn as it runs
• a ? abort one level out of debugger

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Reverse a list

• (defun invert (mylist)
• (inverte-aux mylist () )
• )
• (defun invert-aux (mylist outlist)
• (if (null mylist)
• outlist
• (invert-aux (cdr mylist) (cons (car mylist)
  outlist))
• )
• )
• (invert '(don patti blaz adam)) gt (ADAM BLAZ
  PATTI DON)

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Lambda

• (lambda (x) ( x 1))
• ((lambda (x) ( x 1)) 4) gt 5
• (defun my-f (mylist)
• (if (null mylist)
• ()
• (cons
• ((lambda (x) ( (- x 4) (- x 3))) (car mylist))
• (my-f (cdr mylist))
• )
• )
• )
• (my-f'(1 2 3 4 5)) gt (6 2 0 0 2)

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mapcar

• (defun my-f-two (mylist)
• (mapcar '(lambda (x) ( (- x 4) (- x 3)))
  mylist)
• )
• (my-f-two '(1 2 3 4 5)) gt (6 2 0 0 2)

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Comic from xkcd.com