What are Clojure's Naming Conventions?

Question

You might want to look at the Clojure library coding standards on the developer Wiki - this is probably the most comprehensive list that I've seen.

To your specific points:

1. File names are lowercase, and stored in a directory structure to match the namespace, and end in .clj e.g. "my/special/namespace.clj
2. Functions are dash-separated-lowercase-words, ideally descriptively chosen so that your code is clear and self-documenting. Don't be afraid to re-use good function names in different namespaces (that is what namespaces are for!).
3. Variables (by which I assume you mean parameters, let-bound variables etc.) are also usually dash-separated-lowercase-words. Since code-is-data, I think it is appropriate that functions and data have the same naming convention :-)

You might want to take a look at this non official style guide.

There are some interesting guidelines on naming written by Stuart Sierra which suggest that:

• pure functions should be nouns describing the return value (age instead of calculate-age)
• side-effecting functions should be verbs describing the action (create- for constructing and get- for retrieving), reserving the bang swap! changes to mutable references.
• verbs that can also be nouns should be distinguished as verb phrases (send-message instead of message)
• coercions should name the output type without an arrow prefix (connection instead of ->connection) except when the input type must be explicit (input-type->output-type)
• namespace aliases can save on repetition (products/price instead of products/product-price) and prevent local clashes in let bindings
• functions returning functions should have the -fn suffix

There is an interesting set of naming conventions documented in a comment by Taoensso in his Encore library.

He proposes names using ! for side-effects, ? for booleans, $ for expensive operations, _ as dereffable, * for macros; plus a few other combos.