Functions

What is a Function

A function is a block of organized, reusable code that is used to perform some actions. Function can accept parameters and can return values.

How to Call a Function

To call a function without parameters and not returning anything, type its name and a pair of brackets:

ClearScreen()

To call a function with parameters, but not returning anything, type its name and parameters separated by commas inside a pair of brackets:

DrawText(10, 10, "Hello World")

To call a function returning a value, call it as above, but use the return value in expressions or for assignment:

a = sin ( 3 )
b = cos ( PI () * 2 )

How to Write a New Function

To write a function without parameters and not returning anything, type keyword FUNCTION, function name and a pair of brackets. Then type some code, and finish it with END FUNCTION keywords:

function ClearAndDraw()
	ClearScreen()
	DrawRectangle(100, 100, 300, 200)
end function

To write a function with parameters, but not returning anything, type keyword FUNCTION, function name and type its parameters separated by commas inside a pair of brackets. Then type some code, and finish it with END FUNCTION keywords. Function parameters can be used as local variables inside the function:

function ClearAndDraw(x1, y1, x2, y2)
	ClearScreen()
	DrawRectangle(x1, y1, x2, y2)
end function

To write a function returning a value, write it as above and assign the return value to a local variable named the same as function name:

function ClearDrawAndGetArea(x1, y1, x2, y2)
	ClearScreen()
	DrawRectangle(x1, y1, x2, y2)
	ClearDrawAndGetArea = abs(x2 - x1) * abs(y2 - y1)
end function
area = ClearDrawAndGetArea(100, 100, 300, 200) ' area is 20000

How to Overload a Function

Functions in Toy Basic can be overloaded. To do so, you just need to write another function with the same name and the same number of parameters. The last function will be used:

' This function will not be used, since it is overloaded later
function ClearAndDraw(x1, y1, x2, y2)
	ClearScreen()
	DrawRectangle(x1, y1, x2, y2)
end function

' This function will be used, since it is a correct overload
function ClearAndDraw(x1, y1, x2, y2)
	ClearScreen()
	DrawImageRectangle(x1, y1, x2, y2, $Image)
end function

' This an example of incorrect overload. 
' Number of parameters is different and
' an error will be reported
function ClearAndDraw(x1, y1, x2, y2, x3, y3, x4, y4)
	ClearScreen()
	DrawImageQuad(x1, y1, x2, y2, x3, y3, x4, y4, $Image)
end function

It is common to overload event functions:

function OnKeyboard(char)
	ClearScreen()
	DrawText(100, 100, char)
end function