prev-iter 
prev-iter contains an iterator which allows you to view the previous element.
Usage
Add the following line to your Cargo.toml under the [dependencies] section:
prev-iter = "0.2.0"
Documentation
Documentation is available at docs.rs.
Running tests
cargo test
License
prev-iter is licensed under MPL-2.0 and so are all contributions. Please see the license for more information.