DEFTABLE
Copyright 1992 by Sun Microsystems Inc. (Sun)
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The DEFTABLE macro provides a concise, lightweight notation for defining tables: things you can put key/value pairs into, and retrieve the value from the key. For example, after specifying:
(deftable state :init '((AL Alabama) (AK Alaska) ...))
You can say (get-state ‘AL) to get Alabama. If the need ever arises, you can add to the table with (put-state ‘PR ‘Puerto-Rico), or equivalenty, (setf (get-state ‘PR) ‘Puerto-Rico). You can delete one or clear all entries, and you can use (map-state #’(lambda (abbrev name) …)) to map a function over all entries.
Finally, you can keep track of multiple tables of the same type. For example, you could arrange to have a table for each country, so that:
(get-state 'AZ *USA*) ==> Arizona (get-state 'AZ *CIS*) ==> Azerbaijan
When it comes time to performance-tune your program, you can implement each table type as a hash table, property list, alist, or vector (if the keys are dense small integers), or define your own implementation.
Note that if you evaluate two deftables with the same name, the table created for the first one will not be replaced (because the table is defined with defvar, not defparameter. The default value and any initial values will take effect the second (and subsequent) times, however.
See the article “DEFTABLE: A Macro for Implementing Tables” by Peter Norvig, to appear in Lisp Pointers, for more details.
;;;; Sample Expansion
(deftable state
:init '((AL Alabama) (AK Alaska))) ===>
(eval-when (:compile-toplevel :load-toplevel :execute)
(defun new-state-table (&key (size 100) (test #'equal))
"Create a new table."
(make-hash-table :test test :size size))
(defparameter *state-table-default* nil)
(defvar *state-table* (new-state-table))
(declaim (notinline new-state-table get-state put-state rem-state map-state))
(defsetf get-state (key &optional (table '*state-table*)) (val)
(list 'put-state key val table))
(defun get-state (key &optional (table *state-table*))
"Return 2 values: the val for this key and t, or the default and nil."
(gethash key table *state-table-default*))
(defun put-state (key val &optional (table *state-table*))
"Store val as the value of key in the table."
(setf (gethash key table) val))
(defun rem-state (key &optional (table *state-table*))
"Remove key and it's value from the table."
(remhash key table))
(defun clear-state (&optional (table *state-table*))
"Remove all key/value pairs from the table."
(clrhash table))
(defun map-state (fn &optional (table *state-table*))
"Apply fn to each key and value, in any order."
(maphash fn table))
(initialize-table *state-table* #'put-state '((al alabama) (ak alaska)))
'state)