README.md

Classic File Scanner without Eff

In all the exercises, we will look at variants of a File Scanner. The scanner finds and reports on the largest 10 files under a directory specified by the user, as well as collecting some stats about how many total files and total bytes are found.

This first exercise uses regular Scala features without Eff:

• File system operations are done directly inline, primarily using the java.nio.file.Files API provided in Java 8. This is preferable to the operations offered through the older java.io.File API because error conditions are signalled by an exception rather than simply returning an uninformative null.

• Error handling is by throwing exceptions which will bubble to the top.

Tasks

▶️ Run Code

Run the scanner on current directory with solutionExerciseClassic/run . Does the result seem correct?

Try it on some larger directory of your computer.

🔍 Study Code

Study the algorithm used by the scanner. The key data structure is a PathScan, which contains a sorted list of the largest N files and their sizes in bytes, plus a count of total files scanned and total bytes across all files.

Note how the scanner must combine PathScans of differing subdirectories together to yield a single PathScan that summarizes both the top N files and total files visited. This combine operation has a Monoid structure.

📝 Write Code

Complete the Monoid instance for PathScan.

▶️ Run Code

Run the unit tests with exerciseClassic/test to verify your Monoid implementation.

🔍 Study Code

Examine the ScannerSpec.

Note how much of the test is involved with creating- and cleaning up- actual files. It would be nice is we could separate testing the algorithm from the filesystem. How should this be done?