Overview of the AmFn Wasm.
The AmFn Wasm is an amortization cashflow calculator that utilizes the AmFn engine written in Rust. While in general, a cashflow represents a movement of money, an amortization cashflow usually involves interest changes. An amortization cashflow can be negative, such as car loans, mortgages, etc., or positive, such as annuities, bonds, investments, etc.
The AmFn Wasm can simultaneously handle multiple open cashflows. Each cashflow is represented by a tab. Clicking on a tab shows the coresponding cashflow. Each cashflow has an event grid at the top, an amortization grid under the event grid, a status line under the amortization grid, and summary information that can be shown when needed.
Event-driven
The AmFn Wasm is an "event-driven" amortization cashflow calculator. The top event grid for a cashflow is editable. In contrast, the amortization grid, status line, and summary information are all products of processing the events in the event grid.Cashflow events are always preserved and not merged or lost. One of the benefits of event-driven is that repeatedly asking involved "what if?" questions is a quick and easy task. Another benefit is that events also decrease the amount of user input required to create and actively maintain a cashflow.
Amortization schedule
The continuity of the cashflow is maintained even through certain types of events, such as interest rate changes. This preserves any unresolved accrued interest from previous interest rate periods.
All events are based upon real dates and can occur on "any" date within the cashflow, which can also result in stub periods and odd days interest. This allows for powerful "whatever scenarios" within cashflows that can easily service increasingly competitive, consumer oriented markets and financial products.
When event fields are updated by the user, the amortization grid, status line, and summary information are all automatically recalculated.
Templates
AmFn Wasm can be functionally customized to a high degree by it's built-in template facility in order to create different functional processes for each type of cashflow such as mortgage loans, consumer loans, bonds, annuities, investments, etc.
Locales and initialization.
Multiple locale information is consistently used throughout AmFn Wasm, along with applicable ISO (International Standards Organization) standards, to allow for the simultaneous calculation and display of different currencies, date formats, number formats, and spoken languages. The AmFn Wasm is internationalized and globalized, thus allowing it to be adapted to another spoken language, all from external locale definitions.
A locale is an externally defined collection of JSON and other files under the "locales" folder followed by the locale string (e.g., "locales/en-US"). The locale's files include the user preferences, core locale information, templates, help, and tutorials.
When the AmFn Wasm is initialized, it attempts to determine an appropriate locale by checking "navigator.languages" against the available locales. In the event a locale cannot be found, the default available locale will be used ("en-US").
Event combinations.
A number of approaches can create event combinations meant to handle different scenarios:
-
Combining standard events, as all events are merged into the amortization. For example,
on a loan there might be a normal monthly payment and an annual bump payment. Advantage:
Payments are standard separate events. Disadvantage: More work to recalulate a new
term if the payments amounts change.
- Using event expressions with parameters offers a great deal of flexibility. This is typically accomplished by using template events. For example, the same loan with normal monthly payments and annual bumps can be handled using this method. Advantage: More natural to recalulate a new term if the payments amounts change. Disadvantage: Upfront work to setup in the template if an appropriate template event does not already exist.
An example of the last event combination approach can be found with the "Normal+bump pymt" event in the "Standard Loan" template. When we insert this event into the cashflow, we'll immediately see the following dialog to initially set the parameters (the event parameters can also be subsequently changed):
Event grid keyboard conventions.
When two or more simultaneous keystrokes are involved, each keystroke is visually separated by a plus sign ("+"). For example, "Shift+Enter" means to press the "Shift" and the "Enter" keys simultaneously.
| Keystrokes | Description |
|---|---|
| Enter | Behaves like a Tab except when positioned in the last column of the last row. In that case, a new event is automatically placed into the cashflow if the current event specifies a "next event" name. If the current event does not specify a next event name, the new event dialog is shown to the user allowing the next event to be explicitly selected. |
| Tab | Selects the next cell in the current row unless the last cell of the current row is reached, in which case the first cell of the next row is selected. If the last cell of the last row is reached, the first cell of the first row is then selected. |
| Shift+Tab | Selects the previous cell in the current row unless the first cell of the current row is reached, in which case the last cell of the previous row is selected. If the first cell of the first row is reached, the last cell of the last row is then selected. |
Basic event types.
There are four basic event types in AmFn from which all events are derived. When used with the templates and expressions, the four basic event types provide the necessary basis to create an unlimited number of different kinds of events. The four basic event types are as follows:
Interest change.
Interest change events are used to cause changes in the currently active interest rate event (i.e., method, day-count, nominal annual rate, compounding frequency, effective frequency, etc.). Interest change events run in perpetuity until the end of the cashflow or until explicitly changed.
Principal change.
Principal change events account for any change in the principal balance of a cashflow. The 4 sub-types of principal change events are as follows:
| Label | Description |
|---|---|
| Increase | Increase the principal balance of the cashflow by a certain amount (normally used). |
| Decrease | Decrease the principal balance of the cashflow by a certain amount (normally used). |
| Positive | Assign or overwrite the principal balance of the cashflow by a positive amount (rarely used). |
| Negative | Assign or overwrite the principal balance of the cashflow by a negative amount (rarely used). |
Current value.
Current value events indicate the current value of the cashflow at any point in time. The 3 kinds of current value events are as follows:
| Label | Description |
|---|---|
| Passive | A passive current value does not affect the balance of the cashflow. An example would be reporting the balance of a loan as of a specific date without causing a normal period to be actively split. |
| Active | An active current value event affects the balance of the cashflow. An example would be an initial investment that reports the balance on an annual basis, with no periodic re-investments. |
| Present Value (PV) | The Present Value (PV) current value event is a special form of an active current balance event. This event is normally used to separate the "past" from the "future" as of a certain date. |
Statistic value.
Statistic value events are used to collect and report on totals within the cashflow such as annual, quarterly, trimester, 4-week, 2-year, or any length of period desired by the user. Any number and combination of statistic value events may be used with other statistic events as desired. Statistic value events automatically run in perpetuity until the end of the cashflow or until explicitly discontinued by the user.
User, template and cashflow preferences.
Preference elements exist at the user (top-tier), template (middle-tier) and cashflow (bottom-tier) levels. When new templates or Cashflows are created, preference elements are propagated from the user level to the template level and from the template level to the cashflow level, when the user has explicitly specified that this action is to occur.
All preference elements contain various of fields of information, a descriptor list, and a parameter list that can be used in a number of ways depending upon the level of the preference element.
Locale sensitive information descriptors.
Descriptors (i.e., lists of descriptor elements) exist within user, template and cashflow preferences as well as within each event of a cashflow. When indicated by the user, descriptors are propagated from the user preferences into the template preferences and from the template preferences into the cashflow preferences.
Descriptors are also propagated from the event lists of a particular template name element into the event list of a cashflow when new events are created. However, descriptors are never propagated from the various preferences into the event list of a cashflow.
All descriptors within a descriptor list can be "locale sensitive". That is, each descriptor can define a specific locale where the descriptor will be used. When searching for a descriptor within a descriptor list, AmFn Wasm will always consider the locale first on all applicable levels and then subsequently search for a generic descriptor (i.e., a descriptor with no locale set) only if a descriptor cannot be found for a given locale within all applicable levels.
Descriptors can also define specific codes of information other than locales. These codes are customizable by the user and may include General Ledger codes, Tax codes, or literally any other type of code that make sense to the user.
This is especially useful with event descriptor lists, where certain events may need to be marked for further interpretation on a report or for additional processing by another system.
Interface parameters and expressions.
Interface parameters exist within user, template and cashflow preferences as well as within each event of a cashflow. Parameters are used to supply information to various expressions. The declarations of parameters are normally defined within a template, while the values to the previously defined parameters are usually entered by the user.
AmFn defines a robust expression facility that comes complete with common functions for cashflow oriented tasks, and can even store intermediate results of expressions as variables. More than one expression can be specified within a compound expression.
Expressions can be used within any descriptor element at any level. However, expressions used within certain locations, such as descriptors involved with customization, normally make use of variables that are predefined by AmFn.