An ALT program can be considered to be a advanced type of spreadsheet. For example, with ALT you can create spreadsheets that have ’typed’ cells, and cells that recursively contain other spreadsheets. In this example we create and edit a simple spreadsheet.
First we define the spreadsheet type
_S that only allows cells to contain positive numbers, and has exactly three columns and four rows. Then we create a simple spreadsheet
S0 with three columns
C and three rows
3 (column major ordering). We edit one cell to add a ‘formula’, creating spreadsheet
S1. After that we add an extra row to sum columns, creating spreadsheet
S2. For every spreadsheet we check whether they still conform to type
Notice that the formulas use advanced relative indexing and scoping. This makes it possible to ‘copy’ such formulas into other spreadsheets at different coordinates (aka relative cell references).