http://i-cjw.com/lisp Mon, 09 Jun 2008 12:10:08 +0000 http://backend.userland.com/rss092 en --------------------------------------------------------- Chapter 11 --------------------------------------------------------- Iteration and Block Structure (dotimes (i 4) (format t "~&I is ~S." i)) I is 0. I is 1... (dolist (x '(red green blue) 'flowers) (format t "~&Roses are ~S" x)) Roses are RED Roses are BLUE Roses are GREEN FLOWERS dolist returns the final symbol in its parameters (i.e. Flowers, above) RETURN can be used to break the loop - ... http://i-cjw.com/lisp/2008/06/08/iteration-block-structure/ --------------------------------------------------------- Chapter 10 --------------------------------------------------------- Global Variables (SETF *my-global-variable* 0) -> initializes to zero (defun sell (n) (SETF *my-global-variable* (+ *my-global-variable* n)) (format t "Sold ~S glasses today" *my-global-variable*)) If variable set to FOO, then will fail when try to increment. If variable not initialized to zero, then will fail when incremented. For simple incrementing and decrementing, ... http://i-cjw.com/lisp/2008/06/08/assignment/ --------------------------------------------------------- Chapter 9 --------------------------------------------------------- Input/Output Strings - double quoted: (setf a "this is a string") -> "this is a string" (stringp a) -> T (format t a) -> this is a string -> NIL tilde character leads to special operations ~% -> forces newline (format t "time flies~%like an arrow") -> time flies like an arrow NIL ~& forces a newline, unless the cursor ... http://i-cjw.com/lisp/2008/06/08/inputoutput/ --------------------------------------------------------- Chapter 8 --------------------------------------------------------- Recursion: Double-tail recursion returns one of two results: (DEFUN anyoddp (x) (COND ((null x) NIL) ((oddp (first x)) T) (T (anyoddp (rest x))))) Single-tail recursion returns one result: (DEFUN find-first-atom (x) (COND ((atom x) x) (T (find-first-atom (rest x))))) Augmenting recusion loops using the result to build the final answer: (DEFUN fib (x) (COND ((NULL x) 0) (T (+ x (fib (- x 1)))))) List ... http://i-cjw.com/lisp/2008/06/08/recursion/ --------------------------------------------------------- Chapter 7 --------------------------------------------------------- FUNCALL calls a function on some inputs: (FUNCALL #'cons 'a 'b) -> (a . b) Can also map a function to a symbol: (SETF fn #'cons) (FUNCALL fn 'a 'b) -> (a . b) only ordinary functions should be quoted with #' - macros, symbols or special functions will generate an error (#'IF -> ... http://i-cjw.com/lisp/2008/06/08/applicative-programming/ --------------------------------------------------------- Chapter 6 --------------------------------------------------------- (APPEND '(1 2 3) '(4 5 6)) -> (1 2 3 4 5 6) (APPEND NIL '(1 2 3)) -> (1 2 3) (APPEND '(1 2 3) NIL) -> (1 2 3) (APPEND NIL NIL) -> NIL (APPEND '((1 2) (3 4)) '((5 6) (7 8))) -> ((1 2) (3 4) (5 6) ... http://i-cjw.com/lisp/2008/06/08/list-data-structures/ --------------------------------------------------------- Chapter 5 --------------------------------------------------------- SETF assigns a global variable: (SETF n 1) (SETF x '(1 2 3)) (LENGTH x) -> 3 (REST x) -> (2 3) variables have scope - to create a local variable use LET: (DEFUN MANIP (op x y) (LET ( (SUM (+ x y)) (PROD (* x y)) ) (COND ((EQUAL op 'AVG) (/ SUM 2.0)) ((EQUAL op ... http://i-cjw.com/lisp/2008/06/08/variables-side-effects/ --------------------------------------------------------- Chapter 4 --------------------------------------------------------- Conditionals - IF: (IF (ODDP 5) 'odd 'even) -> odd COND (DEFUN COMPARE-TO (x y) (COND ((EQUAL x y) 'equal) ((> x y) 'x-greater-than-y) (( 2 1) (< 3 4)) ->T (OR (> 1 2) (< 3 4)) -> T AND progresses until it hits a NIL (in which case it returns NIL) or the end of ... http://i-cjw.com/lisp/2008/06/08/conditionals/ --------------------------------------------------------- Chapter 3 --------------------------------------------------------- Numbers, and the symbols NIL and T, evaluate to themselves: 1 -> 1 T -> T NIL -> NIL Evaluation rule for lists - the first element is the function to call, the rest are arguments to the function. (DEFUN my-function (x) (* x 2)) Evaluation rule for symbols - a symbol evaluates to the value ... http://i-cjw.com/lisp/2008/06/08/eval-notation/ --------------------------------------------------------- Chapter 2 --------------------------------------------------------- Each element of a LIST is a CONS cell, linked to the next one and terminated with NIL LENGTH returns the number of elements in a LIST (LENGTH '(1 2 3 4)) -> 4 (LENGTH '(1 (2 3) 4) -> 3 (FIRST '(1 2 3)) -> 1 (SECOND '(1 2 3)) -> 2 (THIRD '(1 ... http://i-cjw.com/lisp/2008/06/08/lists/