Added data integrity tests

[cddr]

Hi,

I showed your project to the author of cells and he was wondering how much of his "Cells Manifesto" is supported. I started writing some tests to see and wondered if you might be interested in including some or all of them in your test suite.

[micha]

Thanks for the tests! More tests never hurt :)

About the Cells Manifesto. I'm sorry to say that I hadn't seen Cells until after we'd written Javelin, so there wasn't any specific attempt to implement those ideas, but I think that Javelin does more or less operate accordingly.

The Javelin Cell Manifesto

Javelin is a full spreadsheet implementation. That is to say,

• it provides two kinds of cells (input and formula)
• formulas may be any procedure (and may perform side-effects)
• changes are propagated through the dependency graph correctly, with no "glitches"
  • each cell "sees" all other cells (the cells it depends on) as if they update simultaneously and atomically
  • formula cells only recompute their values after the cells they depend on have been updated
  • formulas never see the rest of the graph in an "incomplete" state
  • formulas are computed only once per propagation
  • except that formulas are computed only when at least one cell they depend on has changed
• there is no laziness anywhere, as such.
  • spreadsheet evaluation propagates "backwards" compared to Lisp
  • the spreadsheet analog would be pruning formula cells from the propagation graph when the cells they depend on haven't changed
• "Observers" are watches
  • references to cells in watchers defeat glitch elimination—watchers may have an inconsistent view of the cell graph when they run
• cell formulas can be reassigned at runtime by mutating the cell in place
• it's an error to attempt to change the value of a formula cell directly
• it's an error to create a formula cell that results in circular dependencies between formulas

There are two primitive functions from which Javelin cells are built: cell and lift. The cell function creates an input cell. The lift function takes one argument, a function, and returns a function which, when applied to arguments that may include cells, returns a formula cell. e.g

(def a (cell 100)) ;; input cell
(def b (cell 200)) ;; input cell
(def c ((lift +) a b 300) ;; formula cell
@c ;;=> 600
(swap! a inc)
@c ;;=> 601

Does this answer the question?

Thanks again for your patch!