Yeah, the book used to be called "unmakable" when it was referred to being transformed into film. Gilliam did an amazing job, but Hunter had some disagrements with with him. Listen to the commentary by Hunter on the Criterion Edition for more info on this.

The Doc

And you liar, teller of tall tales: you trample all the Lord's commandments underfoot, you murder, steal, commit adultery, and afterward break into tears, beat your breast, take down your guitar and turn sin into a song. Shrewd devil, you know very well that God pardons singers no matter what they do, because he can simply die for a song.