Generic container iteration

with-container-map.lisp

(defgeneric call-with-container-map (container func)
  (:documentation "Iterate over the contents of CONTAINER, calling
  FUNC with the current element of CONTAINER, followed by the index or
  key that corresponds to it."))

(defmethod call-with-container-map ((container array) func)
  (loop for index from 0
     for value across container
     do (funcall func value index)))

(defmethod call-with-container-map ((container list) func)
  (loop for index from 0
     for value in container
     do (funcall func value index)))

(defmethod call-with-container-map ((container hash-table) func)
  (loop for index being the hash-keys of container
     using (hash-value value)
     do (funcall func value index)))

(defmacro with-container-map ((container &optional (value-var '~value) (key-var '~key)) &body body)
  `(call-with-container-map ,container (lambda (,value-var ,key-var)
                                         (declare (ignorable ,value-var ,key-var))
                                         ,@body)))

Hey @spacebat, it's me over from twitter. Nice abstraction and using defmethods specialized around different container type.

Thanks. I like the call-with pattern of having a macro do as little as possible beyond wrapping the body in a lambda and calling a higher order function that does the real work. The runtime cost of possibly creating a closure and calling a function gives you better debugging and easier redefinition.