lisp的功能还是挺强大的，简单的几十行代码就搞定了一个小的“数据库”（经验：调试macro的时候可以用macroexpand-1展开该macro，看是否与设想的一样）。
感受一下lisp吧：
CL-USER> (load "D:/database.lisp")
T
CL-USER> (add-cds)
Title: hacker
Artist: PG
Rating: 10
Ripped[y/n]: (y or n) y
Another? [y/n]: (y or n) n
NIL
CL-USER> (save-db "D:/save.db")
((:TITLE "hacker" :ARTIST "PG" :RATING 10 :RIPPED T))
CL-USER> (add-cds)
Title: painter
Artist: PG
Rating: 10
Ripped[y/n]: (y or n) y
Another? [y/n]: (y or n) n
NIL
CL-USER> (dump-db)
TITLE: painter
ARTIST: PG
RATING: 10
RIPPED: T
TITLE: hacker
ARTIST: PG
RATING: 10
RIPPED: T
NIL
CL-USER> (select (where :title "hacker"))
((:TITLE "hacker" :ARTIST "PG" :RATING 10 :RIPPED T))
CL-USER> (update (where :title "painter") :title "paint")
((:TITLE "paint" :ARTIST "PG" :RATING 10 :RIPPED T)
(:TITLE "hacker" :ARTIST "PG" :RATING 10 :RIPPED T))
代码出自practical common lisp 一书，有改动~
(defvar *db* nil)
(defun make-cd (title artist rating ripped)
(list :title title :artist artist :rating rating :ripped ripped))
(defun add-record (cd) (push cd *db*))
(defun dump-db ()
(dolist (cd *db*)
(format t "~{~a:~10t~a~%~}~%" cd)))
(defun prompt-read (prompt)
(format *query-io* "~a: " prompt)
(force-output *query-io*)
(read-line *query-io*))
(defun prompt-for-cd ()
(make-cd
(prompt-read "Title")
(prompt-read "Artist")
(or (parse-integer (prompt-read "Rating") :junk-allowed t) 0)
(y-or-n-p "Ripped[y/n]: ")))
(defun add-cds ()
(loop (add-record (prompt-for-cd))
(if (not (y-or-n-p "Another? [y/n]: ")) (return))))
(defun save-db (filename)
(with-open-file (out filename :direction :output :if-exists :supersede)
(with-standard-io-syntax
(print *db* out))))
(defun load-db (filename)
(with-open-file (in filename)
(with-standard-io-syntax
(setf *db* (read in)))))
(defun select (selector-fn)
(remove-if-not selector-fn *db*))
(defun make-comparison-expr (field value)
`(equal (getf cd ,field) ,value))
(defun make-comparisons-list (fields)
(loop while fields
collecting (make-comparison-expr (pop fields) (pop fields))))
(defmacro where (&rest clauses)
`#'(lambda (cd) (and ,@(make-comparisons-list clauses))))
;(defun where (&key title artist rating (ripped nil ripped-p))
; #'(lambda (cd)
; (and
; (if title (equal (getf cd :title) title) t)
; (if artist (equal (getf cd :artist) artist) t)
; (if rating (equal (getf cd :rating) rating) t)
; (if ripped-p (equal (getf cd :ripped) ripped) t))))
(defun make-set-expr (field value)
`(setf (getf row ,field) ,value))
(defun make-set-list (fields)
(loop while fields
collecting (make-set-expr (pop fields) (pop fields))))
(defmacro update (selector-fn &rest clauses)
`(setf *db*
(mapcar
#'(lambda (row)
(when (funcall ,selector-fn row) ,@(make-set-list clauses))
row) *db*)))
;(defun update (selector-fn &key title artist rating (ripped nil ripped-p))
; (setf *db*
; (mapcar
; #'(lambda (row)
; (when (funcall selector-fn row)
; (if title (setf (getf row :title) title))
; (if artist (setf (getf row :artist) artist))
; (if rating (setf (getf row :rating) rating))
; (if ripped-p (setf (getf row :ripped) ripped)))
; row) *db*)))
(defun delete-rows (selector-fn)
(setf *db* (remove-if selector-fn *db*)))
posted on 2010-10-01 22:23
hex108 阅读(967)
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