dragsa / zob_int_expressions

Scala Spreadsheets!

This challenge is about implementing simple spreadsheets in Scala. We have created a list of subtasks that will gradually build a more advanced system. Try to implement as many of the subtasks as you can, in the order we have listed them.

The project is built using sbt. To run all the test cases, run sbt test from the terminal or the IDE of your choice.

1 - Expressions

Expressions have one operation, that is to evaluate them. The simplest type of expresssion is the constant, which could be implemented as:

case class Constant(a: Long) {
  def value(): Long = a
}

Having only constant expressions is a bit useless, we want to be able to combine them with operators as well. Those operators can also be expressions. To accomplish that, you might need to use kind of polymorphism. For this task, we want the expression types Constant, Add and Mul, where Add and Mul do addition and multiplication of two expressions.

When this this task is finished, you should be able to fill out the details in ExprTest.scala, and make it run. Feel free to write more tests as well.

2 - A SpreadSheet

A spreadsheet is something which lets you store an expression, in some position. For this task, your positions can be a Char for the column, and an Int for the row.

A spreadsheet should also allow you to evaluate the value of the expression in some position of the spreadsheet.

When you have finished this task, you should be able to implement the test case in SpreadSheetTest.scala.

3 - Cell References

For expressions and spreadsheets to be really useful together, we need to be able to reference a cell in the spreadsheet from an expression. Conceptually, you should be able to create the expression 2 + (the cell ('a',3)), and get a result if there is a value in that cell.

This task might require you to either change the type signature of your expressions, or of the spreadsheet.

Once you have finished this task, you should be able to fill out the test case in SpreadSheetCellRefTest.scala. Additionally, we want you to implement the fibonacci sequence and factorial numbers recursively using cell references, in two columns in the spreadsheet up to a finite row number. For example, if you store the fibonacci sequence in column 'a', then evaluating the spreadsheet at position ('a', 10) should give the value 89.

4 - Expression Parsing

For this final task, we want you to build expressions from a string. For the string representation of the expressions, you can choose between infix operators, postfix operators, or prefix operators.

The tokens in the input string should be:

-- *
-- +
-- integers
-- Cell refs, which are a character followed by an integer, i.e a10

Once you have finished this task, you should be able to run ParserTest.scala.