Calculator
This Brain4it module implements a simple calculator that can perform the four basic arithmetic operations: sum, subtract, multiply and division. It's is a good example to understand how the Brain4it dashboards work.
As shown in the image, the dashboard of this module paints a 3 line display and a numeric pad with some additional keys.
Internally, this module stores 3 variables:
- previous_value: the previous entered number.
- operator: the operator selected (a reference to +, -, * or /).
- current_value: the number that is being entered.
The display widget shows the text returned by the @display exterior function, that is the result of concatenating the previous variables:
(function (context data)
(concat
(if (= null previous_value)
""
(concat previous_value "\n")
)
(if (= null operator)
""
(concat operator "\n")
)
current_value
)
)
When a numeric button is pressed the @digit function is invoked to append the corresponding digit to the current_value variable:
(function (context digit)
(set current_value (concat current_value digit))
(module-notify "@display")
)
The module-notify function is called to notify the clients that the value of @display has changed.
When the user press a operator button (+, -, *, /) the @operator function is executed:
(function (context key)
(do_operation)
(set current_value "")
(set operator (reference key))
(module-notify "@display")
)
This function stores in the operator variable the selected operator and calls the do_operation function to perform the corresponding arithmetic operation:
(function ()
(if (> (length current_value) 0)
(do
(set current_value (number current_value))
(set previous_value
(if (= null operator)
current_value
(if (= null previous_value)
(eval (list operator current_value))
(eval
(list
operator
previous_value
current_value
)
)
)
)
)
)
)
)
