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;;;; l-system.lisp
(in-package #:l-system)
;;; "l-system" goes here. Hacks and glory await!
(defparameter *l-system-clauses* (make-hash-table :test 'equal))
(defun l-system (fn axiom depth)
"Expand axiom into some larger list of symbols.
It can expand to parametric grammar or to context sensitive grammar."
(iter (repeat depth)
(with result = axiom)
(setf result
(funcall fn result))
(finally (return result))))
(defun parametric-grammar (elements)
"Handle parametric grammar."
(iter (for (symbol . parameters) in elements)
(for func = (gethash symbol *l-system-clauses*))
(appending (if (functionp func)
(apply func parameters)
(list `(,symbol ,@parameters))))))
(defun context-sensitive-grammar (elements)
"Handle context sensitive grammar and parametric grammar."
(iter (for elt on elements)
(with symbol0 = nil)
(for (symbol1 . parameters1) = (first elt))
(for symbol2 = (first (second elt)))
(for func = (or (gethash (list symbol0 symbol1 symbol2) *l-system-clauses*)
(gethash symbol1 *l-system-clauses*)))
(appending (if (functionp func)
(apply func parameters1)
(list `(,symbol1 ,@parameters1))))
(setf symbol0 (first (first elt)))))
(defmacro -> (symbol vars &body body)
"Define and set rules to grammar."
`(setf (gethash ',symbol *l-system-clauses*)
#'(lambda ,(append vars '(&rest rest))
(declare (ignorable rest))
,@body)))
(defun unset-rule (symbol)
"Unset rules from grammar."
(setf (gethash symbol *l-system-clauses*)
nil))
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