matrix multiplication

matrices.lisp

(defpackage :matrices
  (:use :cl :iterate)
  (:export multiply))

(in-package :matrices)

(defun multiply (m1 m2)
  (flet ((multiply-row (row column size)
	   (iter
	     (for i :below size)
	     (sum (* (aref m1 row i) (aref m2 i column))))))
    (destructuring-bind (m1-rows m1-columns m2-rows m2-columns)
	(concatenate 'list (array-dimensions m1) (array-dimensions m2))
      (when (eql m1-columns m2-rows)
	(iter
	  (with result = (make-array (list m1-rows m2-columns)))
	  (for column :below m2-columns)
	  (iter
	    (for row :below m1-rows)
	    (setf (aref result row column) (multiply-row row column m2-rows)))
	  (finally (return result)))))))