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FunReverse

Simple Scala CLI app based on Cats, Cats Effect and fs2. The goal of this learning project was to exercise the combined use of these libraries with a simplistic scenario that still transcends single type class/construct/library examples.

Mission Statement

  • A command line REPL that prints the reverse of each input line. Empty line input exits processing.
  • Input/output pairs are appended to a log file together with a time stamp.
  • After REPL exit, read the log file and dump it to an XML file.

Sample Session

$ sbt run
[...]
*** FunReverse ***
Entering an arbitrary line will print the reverse of the input.
Entering an empty line will exit processing.
Binary call log is written to /home/patrick/prog/scala/funreverse/calls.binlog
> test
tset
> blah
halb
>
XML call log has been written to /home/patrick/prog/scala/funreverse/calls.xml
[success] Total time: 19 s, completed Apr 13, 2020 9:49:32 PM
$ cat /home/patrick/prog/scala/funreverse/calls.xml
<calls><call><time>2020-04-13T19:49:28.887Z</time><input>test</input><output>tset</output></call><call><time>2020-04-13T19:49:31.284Z</time><input>blah</input><output>halb</output></call></calls>

Implementation Notes

  • REPL is implemented via Monad#iterateWhile().
  • Logger instance is passed via ReaderT.
  • Log entries are written using scodec and read using scodec-stream.
  • XML is generated using the JDK StAX API.