What is the author's tone in Papillon by Henri Charriere?

The book is written in a sometimes convoluted tone that leaves the reader to determine some aspects of the story that are not stated outright. Some of these are given in clues while others are presented as fact, but not necessarily in an order meant to aid the reader. It seems that the purpose of the book is not to inform the reader as much as to serve as an outlet for Papillion's story, This seems to be the case and it is evident that the story is presented as an autobiographical story for Papillion and his trials during his prison term. The tone of the story is somewhat dark and depressing though Papillion retains an aura of hope and optimism of his potential for both survival and an escape to freedom. This hope is sometimes supplanted by hopelessness and despair. An example of this is the death of Papillion's friend who is murdered and then Papillion's witnessing of sharks devouring the corpse. Papillion also helps fellow prisoner escape but sees the man die. These points may be depressing to most readers, especially because the story is true. The story includes some words peculiar to the situation, such as cavale and "plan," and some sentences and phrases in other languages.