I don't think I've ever seen code (in any language) that restricted itself to the Prelude (or its equivalent). What matters is what typical code looks like, and while I like haskell, I believe it's a major weakness of the language that, whether by design or idiom, typical code appears to prefer terseness over good names, and operators over descriptive function names are the most noticeable aspect of the problem. I think mathematicians could use to learn the lesson that descriptive names are nice, rather than programmers learn the lesson that terse domain-specific operators are better.