MI-AFP homework #05

Homework to practice advanced work with functions and basics of typeclasses

Task

1. You've already done some implementation of area and circumference for various shapes in the third homework. Now you will do something similar, but using typeclasses in Data.Shapes!
   • First, implement instances of Validable for each shape type with function valid that says if given shape is valid (its attributes are acceptable, i.e., not negative, forming a triangle).
   • Then, design on your own the Shape2D typeclass which is a subclass of Validable, define area and circumference (remove dummy ones). During the design consider using valid - for invalid shape, both functions should return zero.
   • Finally, implement instances of Shape2D for each shape type.
2. Your second task is to implement TODOs in Data.Logging.
   • Write custom instances of Show and Ord for type LogMessage according to given test specification.
   • Implement three operators $= (change log level), @@ (combine event sources), and ~~ (event source matching).
   • Use the ~~ operator and one powerful but simple higher-order function to implement logFilter. Pointfree style is required!
3. The final (and also the most interesting) task is to implement functions and instances for next data type to represent integers - the Strinteger (from Data.Strinteger)! It is a representation of an integer as English numeral string, for example, 125 is "one hundred twenty-five".
   • The biggest challenge is to implement functions integer2EngNumeral and engNumeral2Integer (related with pack and unpack). Don't worry, no painful copy-pasting is waiting for you. All English numerals that are needed are already prepared in Data.Strinteger.Helpers. Take a look and feel free to edit as you need. Notice that Strinteger is an instance of Bounded. (Look at hints if getting stuck with those two functions.)
   • After having pack and unpack working, it will be very easy to make instances of Eq, Ord, Num, Enum, and Integral (you might need some more due to dependencies) for the Strinteger.
   • If you liked this task, you can try to extend it, so it also works with special named numbers like 10^100 (Googol) or 10^(10^100) (Googolplex). Or implement functionality of Stricimal - string with decimal numbers (instance of RealFloat and related).

Hints & general requirements:

• Shapes and Logging should not be a problem. With Strinteger there might be a problem if you are still used to imperative processing. Think about elementary steps which needs to be done and what cases can occur - then put the solution together from pieces performing trivial steps. Recall how is the number composed and how do you process it when reading/writing English numeral. Always try to be DRY, reuse code, make simple functions and compose them.
• For joining and splitting strings by defined character, use splitOn and intercalate (similar to words and unwords). You should not hardcode any string or character in Data.Strinteger - use only those defined in Data.Strinteger.Helpers or enhance it.
• Being DRY is essential, do not repeat code. Name expressions to reuse then, introduce helper functions.
• Local names (via where or let-in) in functions should be introduced to make the code more readable. Creating very simple helper functions in module scope is not nice. If you need some complicated functions create separate "private" module.
• Make your code as clean as possible. Prefer pattern matching and syntactic sugar everywhere it is reasonable.
• You must understand your code completely!

Notes

• In case of uncertainty, check the dummy homework to recall what is the homework workflow for this course.
• If you encounter some trouble, create an issue in your repository.
• In case you find a bug or have an idea how to improve assignment project, create an issue or PR in this repository.
• It might happen that tests are not 100% bulletproof, but your solution should be correct. If you want, propose tests enhancements.

License

This project is licensed under the MIT License - see the LICENSE file for more details.