Adding upstream version 0.19.0.upstream/0.19.0upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

17 files changed, 815 insertions, 0 deletions

diff --git a/doc/cpp/data_store/cell_access.rst b/doc/cpp/data_store/cell_access.rst
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@@ -0,0 +1,79 @@
+
+.. highlight:: cpp
+
+Cell Access
+===========
+
+Examples
+--------
+
+You can obtain a :cpp:class:`~ixion::cell_access` instance either from
+:cpp:class:`~ixion::model_context` or :cpp:class:`~ixion::document` class.
+
+Here is an example of how to obtain it from a :cpp:class:`~ixion::model_context` instance::
+
+    ixion::model_context cxt;
+    cxt.append_sheet("Sheet");
+
+    // fill this model context
+
+    ixion::abs_address_t A1(0, 0, 0);
+    ixion::cell_access ca = cxt.get_cell_access(A1);
+
+
+Here is an example of how to obtain it from a :cpp:class:`~ixion::document` instance::
+
+    ixion::document doc;
+    doc.append_sheet("Sheet");
+
+    // fill this document
+
+    ixion::cell_access ca = doc.get_cell_access("A1");
+
+
+Once you have your :cpp:class:`~ixion::cell_access` instance, you can, for instance,
+print the value of the cell as follows::
+
+    switch (ca.get_value_type())
+    {
+        case ixion::cell_value_t::numeric:
+        {
+            double v = ca.get_numeric_value();
+            cout << "numeric value: " << v << endl;
+            break;
+        }
+        case ixion::cell_value_t::string:
+        {
+            std::string_view s = ca.get_string_value();
+            cout << "string value: " << s << endl;
+            break;
+        }
+        case ixion::cell_value_t::boolean:
+        {
+            cout << "boolean value: " << ca.get_boolean_value() << endl;
+            break;
+        }
+        case ixion::cell_value_t::error:
+        {
+            ixion::formula_error_t err = ca.get_error_value();
+            cout << "error value: " << ixion::get_formula_error_name(err) << endl;
+            break;
+        }
+        case ixion::cell_value_t::empty:
+        {
+            cout << "empty cell" << endl;
+            break;
+        }
+        default:
+            cout << "???" << endl;
+    }
+
+The complete source code of this example is avaiable
+`here <https://gitlab.com/ixion/ixion/-/blob/master/doc_example/section_examples/cell_access.cpp>`_.
+
+
+API Reference
+-------------
+
+.. doxygenclass:: ixion::cell_access
+   :members:
diff --git a/doc/cpp/data_store/dirty_cell_tracker.rst b/doc/cpp/data_store/dirty_cell_tracker.rst
new file mode 100644
index 0000000..bf4e20a
--- /dev/null
+++ b/doc/cpp/data_store/dirty_cell_tracker.rst
@@ -0,0 +1,8 @@
+
+.. highlight:: cpp
+
+Dirty Cell Tracker
+==================
+
+.. doxygenclass:: ixion::dirty_cell_tracker
+   :members:
diff --git a/doc/cpp/data_store/document.rst b/doc/cpp/data_store/document.rst
new file mode 100644
index 0000000..3578d57
--- /dev/null
+++ b/doc/cpp/data_store/document.rst
@@ -0,0 +1,18 @@
+
+.. highlight:: cpp
+
+Document
+========
+
+Examples
+--------
+
+Refer to the :ref:`quickstart-document` section for code examples on how to
+use the :cpp:class:`~ixion::document` class.
+
+API Reference
+-------------
+
+.. doxygenclass:: ixion::document
+   :members:
+
diff --git a/doc/cpp/data_store/index.rst b/doc/cpp/data_store/index.rst
new file mode 100644
index 0000000..dd4749c
--- /dev/null
+++ b/doc/cpp/data_store/index.rst
@@ -0,0 +1,13 @@
+
+Data Store
+==========
+
+.. toctree::
+   :maxdepth: 2
+
+   model_context.rst
+   document.rst
+   cell_access.rst
+   dirty_cell_tracker.rst
+   types.rst
+
diff --git a/doc/cpp/data_store/model_context.rst b/doc/cpp/data_store/model_context.rst
new file mode 100644
index 0000000..d0b131d
--- /dev/null
+++ b/doc/cpp/data_store/model_context.rst
@@ -0,0 +1,24 @@
+
+.. highlight:: cpp
+
+Model Context
+=============
+
+Examples
+--------
+
+Refer to the :ref:`quickstart-model-context` section for code examples on how
+to use the :cpp:class:`~ixion::model_context` class.
+
+API Reference
+-------------
+
+.. doxygenclass:: ixion::model_context
+   :members:
+
+.. doxygenstruct:: ixion::config
+   :members:
+
+.. doxygenclass:: ixion::model_iterator
+   :members:
+
diff --git a/doc/cpp/data_store/types.rst b/doc/cpp/data_store/types.rst
new file mode 100644
index 0000000..20bb2ac
--- /dev/null
+++ b/doc/cpp/data_store/types.rst
@@ -0,0 +1,89 @@
+
+Types
+=====
+
+Macros
+------
+
+.. doxygendefine:: IXION_ASCII
+
+
+Primitive Types
+---------------
+
+.. doxygenenum:: ixion::celltype_t
+.. doxygenenum:: ixion::cell_value_t
+.. doxygenenum:: ixion::value_t
+.. doxygenenum:: ixion::table_area_t
+.. doxygenenum:: ixion::formula_name_resolver_t
+.. doxygenenum:: ixion::formula_error_t
+.. doxygenenum:: ixion::formula_result_wait_policy_t
+.. doxygenenum:: ixion::formula_event_t
+.. doxygenenum:: ixion::rc_direction_t
+
+.. doxygentypedef:: ixion::col_t
+.. doxygentypedef:: ixion::row_t
+.. doxygentypedef:: ixion::sheet_t
+.. doxygentypedef:: ixion::rc_t
+.. doxygentypedef:: ixion::string_id_t
+.. doxygentypedef:: ixion::table_areas_t
+.. doxygentypedef:: ixion::formula_tokens_t
+
+.. doxygenvariable:: ixion::empty_string_id
+.. doxygenvariable:: ixion::global_scope
+.. doxygenvariable:: ixion::invalid_sheet
+
+.. doxygenstruct:: ixion::rc_size_t
+.. doxygenstruct:: ixion::formula_group_t
+
+
+Cell Addresses
+--------------
+
+.. doxygenstruct:: ixion::address_t
+   :members:
+
+.. doxygenstruct:: ixion::rc_address_t
+   :members:
+
+.. doxygenstruct:: ixion::abs_address_t
+   :members:
+
+.. doxygenstruct:: ixion::abs_rc_address_t
+   :members:
+
+.. doxygenstruct:: ixion::range_t
+   :members:
+
+.. doxygenstruct:: ixion::abs_range_t
+   :members:
+
+.. doxygenstruct:: ixion::abs_rc_range_t
+   :members:
+
+.. doxygenstruct:: ixion::table_t
+   :members:
+
+.. doxygentypedef:: ixion::abs_address_set_t
+
+.. doxygentypedef:: ixion::abs_range_set_t
+
+.. doxygentypedef:: ixion::abs_rc_range_set_t
+
+
+Column Blocks
+-------------
+
+.. doxygentypedef:: ixion::column_block_handle
+.. doxygentypedef:: ixion::column_block_callback_t
+.. doxygenenum:: ixion::column_block_t
+
+.. doxygenstruct:: ixion::column_block_shape_t
+   :members:
+
+Utility Functions
+-----------------
+
+.. doxygenfunction:: ixion::get_formula_error_name
+
+.. doxygenfunction:: ixion::to_formula_error_type
diff --git a/doc/cpp/formula/formula_cell.rst b/doc/cpp/formula/formula_cell.rst
new file mode 100644
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--- /dev/null
+++ b/doc/cpp/formula/formula_cell.rst
@@ -0,0 +1,10 @@
+
+Formula Cell
+============
+
+.. doxygenclass:: ixion::formula_cell
+   :members:
+
+.. doxygenclass:: ixion::formula_result
+   :members:
+
diff --git a/doc/cpp/formula/formula_engine.rst b/doc/cpp/formula/formula_engine.rst
new file mode 100644
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--- /dev/null
+++ b/doc/cpp/formula/formula_engine.rst
@@ -0,0 +1,19 @@
+
+Formula Engine
+==============
+
+.. doxygenfunction:: ixion::parse_formula_string
+.. doxygenfunction:: ixion::print_formula_tokens
+.. doxygenfunction:: ixion::register_formula_cell
+.. doxygenfunction:: ixion::unregister_formula_cell
+.. doxygenfunction:: ixion::query_dirty_cells
+.. doxygenfunction:: ixion::query_and_sort_dirty_cells
+.. doxygenfunction:: ixion::calculate_sorted_cells
+
+
+Formula Functions
+=================
+
+.. doxygenenum:: ixion::formula_function_t
+.. doxygenfunction:: ixion::get_formula_function_name
+.. doxygenfunction:: ixion::get_formula_function_opcode
diff --git a/doc/cpp/formula/formula_name_resolver.rst b/doc/cpp/formula/formula_name_resolver.rst
new file mode 100644
index 0000000..ea9f988
--- /dev/null
+++ b/doc/cpp/formula/formula_name_resolver.rst
@@ -0,0 +1,10 @@
+
+Formula Name Resolver
+=====================
+
+.. doxygenclass:: ixion::formula_name_resolver
+   :members:
+
+.. doxygenstruct:: ixion::formula_name_t
+   :members:
+
diff --git a/doc/cpp/formula/formula_tokens.rst b/doc/cpp/formula/formula_tokens.rst
new file mode 100644
index 0000000..06d33a0
--- /dev/null
+++ b/doc/cpp/formula/formula_tokens.rst
@@ -0,0 +1,19 @@
+
+Formula Tokens
+==============
+
+.. doxygenstruct:: ixion::formula_token
+   :members:
+
+.. doxygenclass:: ixion::formula_tokens_store
+   :members:
+
+.. doxygenstruct:: ixion::named_expression_t
+   :members:
+
+Utility Functions
+-----------------
+
+.. doxygenfunction:: ixion::get_opcode_name
+
+.. doxygenfunction:: ixion::get_formula_opcode_string
diff --git a/doc/cpp/formula/index.rst b/doc/cpp/formula/index.rst
new file mode 100644
index 0000000..976405a
--- /dev/null
+++ b/doc/cpp/formula/index.rst
@@ -0,0 +1,12 @@
+
+Formula
+=======
+
+.. toctree::
+   :maxdepth: 2
+
+   formula_engine.rst
+   formula_cell.rst
+   formula_tokens.rst
+   formula_name_resolver.rst
+   types.rst
diff --git a/doc/cpp/formula/types.rst b/doc/cpp/formula/types.rst
new file mode 100644
index 0000000..9885512
--- /dev/null
+++ b/doc/cpp/formula/types.rst
@@ -0,0 +1,14 @@
+
+Types
+=====
+
+.. doxygenenum:: ixion::fopcode_t
+
+Matrix
+------
+
+.. doxygenclass:: ixion::matrix
+   :members:
+
+.. doxygenclass:: ixion::numeric_matrix
+   :members:
diff --git a/doc/cpp/index.rst b/doc/cpp/index.rst
new file mode 100644
index 0000000..65e970d
--- /dev/null
+++ b/doc/cpp/index.rst
@@ -0,0 +1,16 @@
+.. highlight:: cpp
+
+.. _index:
+
+C++ API
+=======
+
+.. toctree::
+   :maxdepth: 2
+
+   quickstart/index.rst
+   formula/index.rst
+   data_store/index.rst
+   interface/index.rst
+
+
diff --git a/doc/cpp/interface/index.rst b/doc/cpp/interface/index.rst
new file mode 100644
index 0000000..10fc539
--- /dev/null
+++ b/doc/cpp/interface/index.rst
@@ -0,0 +1,10 @@
+
+Interfaces
+==========
+
+.. doxygenclass:: ixion::iface::session_handler
+   :members:
+
+.. doxygenclass:: ixion::iface::table_handler
+   :members:
+
diff --git a/doc/cpp/quickstart/index.rst b/doc/cpp/quickstart/index.rst
new file mode 100644
index 0000000..5097e02
--- /dev/null
+++ b/doc/cpp/quickstart/index.rst
@@ -0,0 +1,13 @@
+
+.. highlight:: cpp
+
+Quickstart
+==========
+
+.. toctree::
+   :maxdepth: 1
+
+   using_model_context.rst
+   using_document.rst
+
+
diff --git a/doc/cpp/quickstart/using_document.rst b/doc/cpp/quickstart/using_document.rst
new file mode 100644
index 0000000..8c6b779
--- /dev/null
+++ b/doc/cpp/quickstart/using_document.rst
@@ -0,0 +1,143 @@
+
+.. highlight:: cpp
+
+.. _quickstart-document:
+
+Using document class
+====================
+
+In the :ref:`quickstart-model-context` section, we saw an example of how to
+set up a cell value store and run some simple calculations using the
+:cpp:class:`~ixion::model_context` class.  While that approach certainly works
+fine, one large drawback is that you do need to manually handle formula tokenization,
+formula cell registration (and un-registration), as well as to trace which cells
+have their values changed and which formula cells have been created or modified.
+This is because the :cpp:class:`~ixion::model_context` class is designed to only
+handle cell value storage, and all other operations related to formula expressions
+and formula cell (re-)calculations have to be done outside of it.
+
+Luckily, Ixion also provides a higher level document class called
+:cpp:class:`~ixion::document` which internally uses :cpp:class:`~ixion::model_context`
+and handles all the formula cell related operations internally.  This section
+provides an overview of how to use the :cpp:class:`~ixion::document` class to
+do more or less similar things we did in the :ref:`quickstart-model-context`
+section.
+
+First, we need to instantiate the :cpp:class:`~ixion::document` instance and
+insert a sheet named ``MySheet``.
+
+::
+
+    ixion::document doc;
+    doc.append_sheet("MySheet");
+
+Next, like we did in the previous section, we will insert numbers 1 through 10
+in cells A1 through A10::
+
+    for (ixion::abs_address_t pos(0, 0, 0); pos.row <= 9; ++pos.row)
+    {
+        double value = pos.row + 1.0; // Set the row position + 1 as the cell value.
+        doc.set_numeric_cell(pos, value);
+    }
+
+So far we don't see much of a difference from model_context.  Let's now insert
+string values into cells B2 and B3::
+
+    // Insert string values.
+    std::string s = "This cell contains a string value.";
+    doc.set_string_cell("B2", s);
+    doc.set_string_cell("B3", "This too contains a string value.");
+
+Here we see the first difference.  When using :cpp:class:`~ixion::document`,
+You can specify the cell position either by :cpp:struct:`~ixion::abs_address_t`
+as with :cpp:class:`~ixion::model_context`, or by a string whose value is the
+name of the cell address.  The default address syntax for the string cell address
+is "Excel A1" syntax.  You can pick a different syntax by passing a value of type
+:cpp:enum:`~ixion::formula_name_resolver_t` to the constructor.
+
+It's worth noting that, when specifying the cell position as a string value and
+the sheet name is omitted, the first sheet is implied.  You can also specify
+the sheet name explicitly as in the following::
+
+    doc.set_string_cell("MySheet!B4", "Yet another string value.");
+
+For a document with only one sheet, it makes no difference whether to include
+the sheet name or leave it out, but if you have more than one sheet, you need to
+specify the sheet name when specifying a cell position on sheets other than the
+first one.
+
+Now, let's insert a a formula into A11 to sum up values in A1:A10, and calculate
+it afterward::
+
+    doc.set_formula_cell("A11", "SUM(A1:A10)");
+    doc.calculate(0);
+
+And fetch the calculated value in A11 and see what the result is::
+
+    double value = doc.get_numeric_value("A11");
+    cout << "value of A11: " << value << endl;
+
+You should see the following output:
+
+.. code-block:: text
+
+    value of A11: 55
+
+It looks about right.  The :cpp:func:`~ixion::document::calculate` method takes one
+argument that is the number of threads to use for the calculation.  We pass 0 here to
+run the calculation using only the main thread.
+
+Now, let's re-write the formula in cell A11 to take the average of A1:A10 instead,
+run the calculation again, and check the value of A11::
+
+    // Insert a new formula to A11.
+    doc.set_formula_cell("A11", "AVERAGE(A1:A10)");
+    doc.calculate(0);
+
+    value = doc.get_numeric_value("A11");
+    cout << "value of A11: " << value << endl;
+
+The output says:
+
+.. code-block:: text
+
+    value of A11: 5.5
+
+which looks right.  Note that, unlike the previous example, there is no need to un-register
+and register cell A11 before and after the edit.
+
+Lastly, let's insert into cell A10 a new formula that contains no references to other cells.
+As this will trigger a re-calculation of cell A11, we will check the values of both A10
+and A11::
+
+    // Overwrite A10 with a formula cell with no references.
+    doc.set_formula_cell("A10", "(100+50)/2");
+    doc.calculate(0);
+
+    value = doc.get_numeric_value("A10");
+    cout << "value of A10: " << value << endl;
+
+    value = doc.get_numeric_value("A11");
+    cout << "value of A11: " << value << endl;
+
+The output will be:
+
+.. code-block:: text
+
+    value of A10: 75
+    value of A11: 12
+
+Notice once again that there is no need to do formula cell registration nor manual tracking
+of dirty formula cells.
+
+
+Conclusion
+----------
+
+In this section, we have performed the same thing we did in the :ref:`quickstart-model-context`
+section, but with much less code, and without the complexity of low-level formula expression
+tokenization, formula cell registration, or manual tracking of modified cells.  If you are
+looking to leverage the functionality of Ixion but don't want to deal with lower-level formula
+API, using the :cpp:class:`~ixion::document` class may be just the ticket.
+
+The complete source code of this example is avaiable `here <https://gitlab.com/ixion/ixion/-/blob/master/doc_example/document_simple.cpp>`_.
diff --git a/doc/cpp/quickstart/using_model_context.rst b/doc/cpp/quickstart/using_model_context.rst
new file mode 100644
index 0000000..f37bd5f
--- /dev/null
+++ b/doc/cpp/quickstart/using_model_context.rst
@@ -0,0 +1,318 @@
+
+.. highlight:: cpp
+
+.. _quickstart-model-context:
+
+Using model_context class
+=========================
+
+Create a model context instance
+-------------------------------
+
+When using ixion, the very first step is to create a :cpp:class:`~ixion::model_context`
+instance::
+
+    ixion::model_context cxt;
+
+The :cpp:class:`~ixion::model_context` class represents a document model data
+store that stores cell values spreading over one or more sheets.  At the time of construction,
+the model contains no sheets. So the obvious next step is to insert a sheet::
+
+    // First and foremost, insert a sheet.
+    cxt.append_sheet("MySheet");
+
+The :cpp:func:`~ixion::model_context::append_sheet` method will append a new sheet to
+the model.  You need to give a name when appending a sheet, and the name must be unique
+for each sheet.
+
+.. note::
+
+    Each sheet has a fixed size which cannot be changed once the :cpp:class:`~ixion::model_context`
+    object is instantiated.  The default sheet size is 1048576 rows by 16384 columns.  You can
+    specify a custom sheet size by passing a desired sheet size value to the
+    :cpp:class:`~ixion::model_context` constructor at the time of instantiation.
+
+
+Populate model context with values
+----------------------------------
+
+Now that you have your first sheet inserted, let's put in some numeric values.  In this example,
+we'll insert into A1:A10 their respective row positions.  To insert a numeric value, you use
+:cpp:func:`~ixion::model_context::set_numeric_cell` which takes the position of the cell as its
+first argument and the value to set as its second argument.  You need to use :cpp:class:`~ixion::abs_address_t`
+to specify a cell position.
+
+::
+
+    // Now, populate it with some numeric values in A1:A10.
+    for (ixion::abs_address_t pos(0, 0, 0); pos.row <= 9; ++pos.row)
+    {
+        double value = pos.row + 1.0; // Set the row position + 1 as the cell value.
+        cxt.set_numeric_cell(pos, value);
+    }
+
+Note that, since row and column positions are internally 0-based, we add one to emulate how the row
+positions are presented in typical spreadsheet program.
+
+Inserting a string value can be done via :cpp:func:`~ixion::model_context::set_string_cell` in one
+of two ways.  The first way is to store the value to a type that decays to ``std::string_view``, such
+as ``std::string``, char array, or string literal, and pass it to the method directly::
+
+    // Insert a string value into B2.
+    ixion::abs_address_t B2(0, 1, 1);
+    std::string s = "This cell contains a string value.";
+    cxt.set_string_cell(B2, s);
+
+    // Insert a literal string value into B3.
+    ixion::abs_address_t B3(0, 2, 1);
+    cxt.set_string_cell(B3, "This too contains a string value.");
+
+The second way is to add your string to the model_context's internal string pool first which will return its
+string ID, and pass that ID to the method::
+
+    // Insert a string value into B4 via string identifier.
+    ixion::string_id_t sid = cxt.add_string("Yet another string value.");
+    ixion::abs_address_t B4(0, 3, 1);
+    cxt.set_string_cell(B4, sid);
+
+The model_context class has two methods for inserting a string to the string pool:
+:cpp:func:`~ixion::model_context::add_string` and :cpp:func:`~ixion::model_context::append_string`.  The
+:cpp:func:`~ixion::model_context::add_string` method checks for an existing entry with the same string value
+upon each insertion attempt, and it will not insert the new value if the value already exists in the pool.
+The :cpp:func:`~ixion::model_context::append_string` method, on the other hand, does not check the pool for
+an existing value and always inserts the value.  The :cpp:func:`~ixion::model_context::append_string` method
+is appropriate if you know all your string entries ahead of time and wish to bulk-insert them.  Otherwise
+using :cpp:func:`~ixion::model_context::add_string` is appropriate in most cases.
+
+
+Insert a formula cell into model context
+----------------------------------------
+
+Inserting a formula cell requires a few extra steps.  First, you need to tokenize your formula string, and
+to do that, you need to create an instance of :cpp:class:`~ixion::formula_name_resolver`.  The
+formula_name_resolver class is responsible for resolving "names" into references, functions, and named
+expressions names.  Ixion provides multiple types of name resolvers, and you specify its type when passing
+an enum value of type :cpp:enum:`~ixion::formula_name_resolver_t` when calling its static
+:cpp:func:`ixion::formula_name_resolver::get` function.  In this example, we'll be using the Excel A1
+syntax::
+
+    // Tokenize formula string first.
+    std::unique_ptr<ixion::formula_name_resolver> resolver =
+        ixion::formula_name_resolver::get(ixion::formula_name_resolver_t::excel_a1, &cxt);
+
+You can also optionally pass a memory address of your :cpp:class:`~ixion::model_context` instance which is
+required for resolving sheet names.  You can pass a ``nullptr`` if you don't need to resolve sheet names.
+
+Next, let's create a formula string we want to tokenize.  Here, we are inserting a formula expression
+**SUM(A1:A10)** into cell A11::
+
+    ixion::abs_address_t A11(0, 10, 0);
+    ixion::formula_tokens_t tokens = ixion::parse_formula_string(cxt, A11, *resolver, "SUM(A1:A10)");
+
+To tokenize a formula string, you call the :cpp:func:`ixion::parse_formula_string` function and pass
+
+* a model_context instance
+* the position of the cell to insert the formula into,
+* a formula_name_resolver instance, and
+* the formula string to tokenize.
+
+The function will then return a sequence of tokens representing the original formula string.  Once you
+have the tokens, you can finally pass them to your model_context instance via
+:cpp:func:`~ixion::model_context::set_formula_cell`::
+
+    // Set the tokens into the model.
+    const ixion::formula_cell* cell = cxt.set_formula_cell(A11, std::move(tokens));
+
+There is a few things to note. First, you need to *move* your tokens to the method since instances of
+type :cpp:type:`ixion::formula_tokens_t` are non-copyable and only movable.  Second, the method returns
+a pointer to the formula cell instance that just got inserted into the model. We are saving it here
+to use it in the next step below.
+
+When inserting a formula cell, you need to "register" it so that the model can record its reference
+dependencies via :cpp:func:`~ixion::register_formula_cell`::
+
+    // Register this formula cell for automatic dependency tracking.
+    ixion::register_formula_cell(cxt, A11, cell);
+
+Without registering formula cells, you won't be able to determine which formula cells to re-calculate
+for given modified cells.  Here we are passing the pointer to the formula cell returned from the previous
+call.  This is optional, and you can pass a ``nullptr`` instead. But by passing it you will avoid the
+overhead of searching for the cell instance from the model.
+
+
+Calculate formula cell
+----------------------
+
+Now that we have the formula cell in, let's run our first calculation.  To calcualte formula cells, you
+need to first specify a range of modified cells in order to query for all formula cells affected by it
+either directly or indirectly, which we refer to as "dirty" formula cells.  Since this is our initial
+calculation, we can simply specify the entire sheet to be "modified" which will effectively trigger all
+formula cells::
+
+    ixion::rc_size_t sheet_size = cxt.get_sheet_size();
+    ixion::abs_range_t entire_sheet(0, 0, 0, sheet_size.row, sheet_size.column); // sheet, row, column, row span, column span
+    ixion::abs_range_set_t modified_cells{entire_sheet};
+
+We will then pass it to :cpp:func:`~ixion::query_and_sort_dirty_cells` to get a sequence of formula cell
+addresses to calculate::
+
+    // Determine formula cells that need re-calculation given the modified cells.
+    // There should be only one formula cell in this example.
+    std::vector<ixion::abs_range_t> dirty_cells = ixion::query_and_sort_dirty_cells(cxt, modified_cells);
+    cout << "number of dirty cells: " << dirty_cells.size() << endl;
+
+Since so far we only have one formula cell, this should only return one range with the size of one row and one column.  You
+will see the following output:
+
+.. code-block:: text
+
+    number of dirty cells: 1
+
+Let's inspect which cell it actually refers to::
+
+    cout << "dirty cell: " << dirty_cells[0] << endl;
+
+which will print:
+
+.. code-block:: text
+
+    dirty cell: (sheet:0; row:10; column:0)-(sheet:0; row:10; column:0)
+
+confirming that it certainly points to cell A11.  Finally, pass this to :cpp:func:`~ixion::calculate_sorted_cells`::
+
+    // Now perform calculation.
+    ixion::calculate_sorted_cells(cxt, dirty_cells, 0);
+
+to calculate cell A11.  After that, you can retrieve the result of the calculation by calling
+:cpp:func:`~ixion::model_context::get_numeric_value` for A11::
+
+    double value = cxt.get_numeric_value(A11);
+    cout << "value of A11: " << value << endl;
+
+You will see the following output:
+
+.. code-block:: text
+
+    value of A11: 55
+
+
+Modify formula cell
+-------------------
+
+Let's say you need to overwrite the formula in A11 to something else.  The steps you need to take
+are very similar to the steps for inserting a brand-new formula cell, the only difference being
+that you need to "unregister" the old formula cell before overwriting it.
+
+Let's go through this step by step.  First, create new tokens to insert::
+
+    // Insert a new formula to A11.
+    tokens = ixion::parse_formula_string(cxt, A11, *resolver, "AVERAGE(A1:A10)");
+
+This time we are inserting the formula **AVERAGE(A1:A10)** in A11 to overwrite the previous one
+**SUM(A1:A10)**.  Before inserting these tokens, first unregister the current formula cell::
+
+    // Before overwriting, make sure to UN-register the old cell.
+    ixion::unregister_formula_cell(cxt, A11);
+
+This will remove the dependency information of the old formula from the model's internal tracker.
+Once that's done, the rest is the same as inserting a new formula::
+
+    // Set and register the new formula cell.
+    cell = cxt.set_formula_cell(A11, std::move(tokens));
+    ixion::register_formula_cell(cxt, A11, cell);
+
+Let's re-calculate the new formula cell.  The re-calculation steps are also very similar to the initial
+calculation steps.  The first step is to query for all dirty formula cells.  This time, however, we don't
+query based on which formula cells are affected by modified cells, which we'll specify as none.  Instead,
+we query based on which formula cells have been modified, which in this case is A11::
+
+    // This time, we know that none of the cell values have changed, but the
+    // formula A11 is updated & needs recalculation.
+    ixion::abs_range_set_t modified_formula_cells{A11};
+    dirty_cells = ixion::query_and_sort_dirty_cells(cxt, ixion::abs_range_set_t(), &modified_formula_cells);
+    cout << "number of dirty cells: " << dirty_cells.size() << endl;
+
+As is the first calculation, you should only get one dirty cell address from the :cpp:func:`~ixion::query_and_sort_dirty_cells`
+call.  Running the above code should produce:
+
+.. code-block:: text
+
+    number of dirty cells: 1
+
+The rest should be familiar::
+
+    // Perform calculation again.
+    ixion::calculate_sorted_cells(cxt, dirty_cells, 0);
+
+    value = cxt.get_numeric_value(A11);
+    cout << "value of A11: " << value << endl;
+
+You should see the following output when finished:
+
+.. code-block:: text
+
+    value of A11: 5.5
+
+
+Formula cell with no references
+-------------------------------
+
+Next example shows a scenario where you want to overwrite a cell in A10, which
+currently stores a numeric value, with a formula cell that references no other
+cells.  Let's add the new formula cell first::
+
+    // Overwrite A10 with a formula cell with no references.
+    ixion::abs_address_t A10(0, 9, 0);
+    tokens = ixion::parse_formula_string(cxt, A10, *resolver, "(100+50)/2");
+    cxt.set_formula_cell(A10, std::move(tokens));
+
+Here, we are not registering this cell since it contains no references hence it
+does not need to be tracked by dependency tracker.  Also, since the previous
+cell in A10 is not a formula cell, there is no cell to unregister.
+
+.. warning::
+
+    Technically speaking, every formula cell that contains references to other
+    cells or contains at least one volatile function needs to be registered.
+    Since registering a formula cell that doesn't need to be registered is
+    entirely harmless (albeit a slight overhead), it's generally a good idea to
+    register every new formula cell regardless of its content.
+
+    Likewise, unregistering a formula cell that didn't need to be registered
+    (or wasn't registered) is entirely harmless.  Even unregistering a cell
+    that didn't contain a formula cell is harmless, and essentially does
+    nothing.  As such, it's probably a good idea to unregister a cell whenever
+    a new cell value is being placed.
+
+Let's obtain all formula cells in need to re-calculation::
+
+    modified_formula_cells = { A10 };
+    dirty_cells = ixion::query_and_sort_dirty_cells(cxt, ixion::abs_range_set_t(), &modified_formula_cells);
+    cout << "number of dirty cells: " << dirty_cells.size() << endl;
+
+Here, we are only passing one modified formula cell which is A10, and no other
+cells being modified.  Since cell A11 references ``A1:A10`` and A10's value has
+changed, this should also trigger A11 for re-calculation.  Running this code
+should produce the following output:
+
+.. code-block:: text
+
+    number of dirty cells: 2
+
+Let's calculate all affected formula cells and check the results of A10 and A11::
+
+    ixion::calculate_sorted_cells(cxt, dirty_cells, 0);
+    value = cxt.get_numeric_value(A10);
+    cout << "value of A10: " << value << endl;
+    value = cxt.get_numeric_value(A11);
+    cout << "value of A11: " << value << endl;
+
+Running this code should produce the following output:
+
+.. code-block:: text
+
+    value of A10: 75
+    value of A11: 12
+
+The complete source code of this example is avaiable `here <https://gitlab.com/ixion/ixion/-/blob/master/doc_example/model_context_simple.cpp>`_.
+