"What exactly is the “Great List Refactor” (GLR)? For several years Rakudo developers and users have identified a number of problems with the existing implementation of list types — most notably performance. But we’ve also observed the need for user-facing changes in the design, especially in generating and flattening lists. So the term GLR now encompasses all of the list-related changes that seem to want to be made."
Larry goes by the handle TimToady
http://imgur.com/1Vrpl2G