Editing Spreadsheet (section)

==== Values ====
A value can be entered from the computer keyboard by directly typing into the cell itself. Alternatively, a value can be based on a formula (see below), which might perform a calculation, display the current date or time, or retrieve external data such as a stock quote or a database value.

<blockquote>'''The Spreadsheet ''Value Rule'''''

Computer scientist [[Alan Kay]] used the term ''value rule'' to summarize a spreadsheet's operation: a cell's value relies solely on the formula the user has typed into the cell.<ref>{{cite journal | last1=Kay | first1=Alan | author-link=Alan Kay | title=Computer Software | journal =Scientific American | volume =251 | issue =3 | pages =52–59 |date=September 1984 | doi=10.1038/scientificamerican0984-52  | pmid=6390676 | last2=Goldstein | first2=JL| bibcode=1984SciAm.251c..52K }} – Value Rule</ref> The formula may rely on the value of other cells, but those cells are likewise restricted to user-entered data or formulas. There are no 'side effects' to calculating a formula: the only output is to display the calculated result inside its occupying cell. There is no natural mechanism for permanently modifying the contents of a cell unless the user manually modifies the cell's contents. In the context of programming languages, this yields a limited form of first-order [[functional programming]].<ref>{{cite journal|last1=Burnett |first1=Margaret|author1-link=Margaret Burnett |last2=Atwood |first2=J. |last3=Walpole Djang |first3=R. |last4=Reichwein |first4=J. |last5=Gottfried |first5=H. |last6=Yang |first6=S. |title=Forms/3: A first-order visual language to explore the boundaries of the spreadsheet paradigm |journal=Journal of Functional Programming |volume=11 |issue=2 |pages=155–206 |date=March 2001 |doi=10.1017/S0956796800003828|s2cid=18730312}}</ref>
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