Version 1, March 1993
It is an error if element-setter cannot successfully set the element of a sequence. This design note requires an error to be signaled in that case, preventing programs from silently returning an incorrect result or otherwise failing.
Specify that if element-setter cannot successfully set the element of a sequence, it should signal an error. The second paragraph of the description of element-setter on page 127 of the Dylan manual should be changed to read, "An error is signaled if a program calls elementsetter with a key that is not already a key to collection, unless the collection supports the dynamic addition of keys and adds the key and new-value."
Next chapter: #11: Last-Setter (Addition)