Addresses Julien's review no.5:

- Stack of varinfos instead of list of varinfos
- stmts_block -> block_to_stmt, which results in less @
- fold_right instead of map+ref
- Optimizing with SkipChildren
- Useless parentheses. Typo. Indentation. No if not then else. begin...end instead of (...) for imperative constructs.