A brief passage from my current reading:
Not only does the process employed by Roussel for the composition of his prose works have the immense interest of adding up to a deliberate promotion of language to the rank of creative agent, instead of contenting itself with using it as an agent of execution, but it seems that the subjugation to a specious and arbitrary law (obliging a concentration on the difficult resolution of a problem whose given facts are as independent as possible of each other) has as a consequence a distraction whose liberating power appears much more efficacious than the abandon, pure and simple, implied by the use of a process like automatic writing. Aiming at an almost total detachment from everything that is nature, feeling and humanity, and working laboriously over materials apparently so gratuitous that they were not suspect to him, Roussel arrived by this paradoxical method at the creation of authentic myths, in which his affectivity is reflected in a more or less direct or symbolic way, as it is shown by the frequency of certain themes which constitute the leitmotivs of his work and of which the omnipotence of science, the close relation between microcosm and macrocosm, ecstasy, Eden, the treasure to be discovered or the riddle to be solved, artificial survival and post mortem states, masks and costumes, as well as many themes which could be interpreted as stemming from fetishism or sado-masochism, constitute examples (here enumerated without any attempt at a methodical inventory).
–Michel Leiris, from “Conception and Reality in the Work of Raymond Roussel” (1954), translated by John Ashbery and published in Raymond Roussel: Life, Death, and Works (Atlas Press, 1987), 79-80.
My italics, to point at this very Oulipian statement (six years before the founding) proclaiming constraint as opposed to automatic writing. Like Queneau, Leiris was also a former Surrealist. Roussel, needles to say, is one of the authors the Oulipo hold dear.