As far as I can tell pattern matching was first proposed as a language feature by Burstall (1969). However, it was a proposal for a feature in the language ISWIM, which itself never had a completed implementation.
F. V. McBride’s Ph.D. dissertation (1970) presented an implementation of a pattern matcher based on a modification of the Lisp 1.5 metacircular interpreter.
Are there any earlier implementations of pattern matching as a programming language feature than this?
(Note I am not interested in pattern matching in the sense of regular expressions on strings, whose history is basically well known.)