Abbreviated parsing example

gistfile1.lisp

(defparameter *input-string*
  "(tiles 2 2
       (tile 0 0 TTERMLTERM EMPTY16X2 0)
       (tile 1 1 TL UL 7
             (primitive_site RLL_X0Y25 RESERVED_LL internal 8)
             (primitive_site DCI7 DCI internal 13)
             (primitive_site DCI0 DCI internal 13)
             (primitive_site PMV PMV internal 8)
             (primitive_site DCIRESET7 DCIRESET internal 1)
             (primitive_site DCIRESET0 DCIRESET internal 1)
             (primitive_site VCC_X0Y25 VCC internal 1)))")



(defgeneric parse-fpga-expr (type rest)
  (:documentation "Parse an expression.  Specialize `TYPE` on `(eql
'SYMBOL)`.  Meant to be called recursively."))

(defmethod parse-fpga-expr (type rest)
  (format t "Unhandled type: ~S~%" type))

(defmethod parse-fpga-expr ((type (eql 'tiles)) rest)
  (destructuring-bind (h w &rest exprs) rest
    (let ((array (make-array (* h w))))
      (loop for expr in exprs
            for i from 0
            do (setf (aref array i)
                     (parse-fpga-expr (car expr) (cdr expr))))
      (make-array (list h w) :displaced-to array))))

(defmethod parse-fpga-expr ((type (eql 'tile)) rest)
  (destructuring-bind (x y a b e &rest exprs) rest
    (list a b (length exprs))))

(defun parse-fpga (list)
  (parse-fpga-expr (car list) (cdr list)))

(parse-fpga (read-from-string *input-string*))