Excelent

Haskell application for spreadsheet calculations

Authors:
Curtis Chin Jen Sem - 5601118
Daniel Kamphorst - 6050107 Noud Savenije - 4302907

Usage:

The environment the program start with contains a chain of integer references, a chain referencing an empty cell, and a chain referencing a cycle.

• Arrow keys to move
• Switching modes is done using the Enter key, there are 2 modes
  • Edit mode where it is possible to edit the expression in the current cell
  • View mode where navigation is possible
• The Escape key exits the program
• Expression notation:
  • Integers: 1, -2, 123213
  • Double: 1.0, 2.01, 1.0e-12
  • References: Tuples are written as (y, x) (or (rows, columns))
    • Absolute references: (1, 3), (91, 1212)
    • Relative references: $(0, 0), $(1, 0)
  • Plus: $(0, 0) + 3, 1.0 + $(1, 0)

Supported functionality

• Expressions
  • Empty
  • Literals (Integers, Doubles)
  • References (Relative, Absolute)
  • Operators (+)
• Seperate layers for expressions and values
  • Both layers use Data.Map as underlying data store, so the size of the sheet is limited by memory (and or traversal time of Data.Map, considering lookup isn't constant)
  • Ensures that expressions are evaluated at most once
  • The moment a cell is evaluated, the value is inserted into the view layer of the environment and reused
  • Any expression containing a reference first checks if that reference has been calculated before
• Graph evaluation
  • Only update the necessary cells when inserting
  • Cycle detection
• Type errors, errors and warnings.
  • We differentiate between a cycle itself, and referencing cycles. Both are treated as errors.
  • Referencing an empty cell is treated as a warning due to an empty cell maybe being useful in some way.
  • However, using that empty reference in an operation results in a type error. Same with using a reference to a cell containing an error.
• Multiple types
  • Type checker implemented which inserts type errors where relevant into the view
  • Unable to do operations on expressions of different types
  • Types currently implemented: Int, Float, Empty, Error
  • We decided against int-to-float coercion to demonstrate the type checkers ability to handle the possible future extension of currencies

Folder structure

• app/
  • Main.hs: Contains the brick application which makes using the necessary functions from the library
• src/
  • Excelent/
    • Definition.hs: Contains the data definitions used in the rest of the application. Also calls the necessary template haskell functions from the relevant libraries
    • Parser.hs: Contains the expression parser
    • Print.hs: Contains usefull functions for printing the content of cells
    • Eval/
      • Eval: Contains the expression evaluating function
      • Graph: Contains functions for generating graphs from expressions. Also contains the code for complete, partial updates and error detection.
      • Checker: Contains the type checking function