# Elm-Spreadsheet

Elm-spreadsheet provides the means to represent and compute with
spreadsheets. A spreadsheet is a two-dimensional array
of cells, each of which may contain either data (values) or formulas.
To evaluate a spreadsheet is to apply the formulas to create
a new spreadsheet.  If the new spreadsheet contains no formulas,
we say that it is _fully evaluated._  The `eval` function calls itself
repeatedly so as to attempt full evaluation.

## Representation

A Spreadsheet is defined internally as an `Array2D Cell`. 
Externally, it can be represented as a string, with cells separated by semicolons.  Cells
are referred to in the same way as in Excel.
    
    
    ss = """
    100; 1.1; mul A1,A2
    120; 1.4; mul B1,B2
    140; 0.8; mul C1,C2
    -;   add A2:C2; add A3:C3
    """

   
The entry `mul A1,A2` means multiply the contents of cell A1 by the
contents of cell A2. The entry `add A2:C2` means add the entries in column 2 between rows A and C.

Use 

```elm
   read: String -> Spreadsheet
``` 

to compute the internal representation as `Array2D Cell`,  use 

```elm
   eval : Spreadsheet -> Spreadsheet
``` 

to evaluate the formulas in a spreadsheet, and use 

```elm
  print : Spreadsheet -> String
``` 

to render the result back into text:


```elm
   > ss |> read |>  eval |> print
  "100; 1.1; 110\n120; 1.4; 168\n140; 0.9; 126\n-; 3.4; 404"
```

Thus the result is the fully evaluated spreadsheet


    100; 1.1; 110
    120; 1.4; 168
    140; 0.9; 126
    -;   3.4; 404


## Operations

Currently the operations implemented are limited:

    add A1,H4   -- cellwise addition
    mul A1,H4   -- cellwise multiplication
    sub A1,H4   -- cellwise subtraction
    div A1,H4   -- cellwise division

    add B2:B9   -- add the elements of row B from columns 2 through 9
    add B2:Q2   -- add the elements of column 2 from rows B through Q

More operations later.