This paper describes a recent addition to LOLC, a text-based environment for collaborative improvisation for laptop ensembles, incorporating a machine musician that plays along with human performers. The machine musician LOLbot analyses the patterns created by human performers and the composite music they create as they are layered in performance. Based on user specified settings, LOLbot chooses appropriate patterns to play with the ensemble, either to add contrast to the existing performance or to be coherent with the rhythmic structure of the performance. The paper describes the background and motivations of the project, outlines the design of the original LOLC environment and describes the architecture and implementation of LOLbot.