Similar to Pratchett's later books -- and Iris Murdoch, as mentioned in another comment -- are the late works of the composer Iannis Xenakis. As long as a decade before he was forced to withdraw from public due to dementia, his music underwent a very peculiar stylistic change where the immense complexity of the earlier pieces (Xenakis built his career on combining music with his work as a modernist architect and erstwhile student of maths) gave way to a very repetitive, single-minded sort of texture.