Coding conventions

Here are some coding conventions that we should adhere to (in random order).

Reserve the use of exceptions for cases where program execution should be aborted. That is, there should only be one try ... with block in the entire code base, namely in the very top-level error handling function in bin/raven.ml. Use Option.t and friends instead of exceptions in other cases. Learn about monads/applicatives if you want nice syntax.
Do not write directly to standard output / standard error. Use the Logs module.
Use begin ... end blocks instead of ( ... ) whenever it improves code readability (e.g. for nested match expressions).
When the code of a lambda abstraction that is passed to a higher-order function spans many lines, replace it by an appropriately named function.
Avoid code duplication. When you are tempted to copy a large chunk of code, don't be lazy. Refactor it into a new function.

Try to keep error handling local. Instead of writing code like this:

(match ... with
| pattern(val) -> (* do a long complex computation with val *)
| ... | ... | -> a bunch of error cases)

write it like this:

let val = match ... with
| pattern(val) -> val
| ... | ... | -> a bunch of error cases
in 
(* do a long complex computation with val *)

This increases the readability of the code.

Provide feedback