Basic concepts > Function calls

System functions

GPScript includes a large and growing collection of system functions for a variety of purposes such as math functions (rounding or scaling numbers), creation and modification of MIDI messages, management of function generators.

User functions

You can also write your own functions in GPScript.

Syntax:

Function <name> ([<identifier> : <type> [, <identifier> : <type>]]) [Autotype] [Returns <type>]
<Local variable declarations>
<Statements>
End

Functions must have a unique name. Zero or more parameters can be defined and parameters are always passed in by value. Note that types such as Widgets, Plugins and dynamic arrays are objects and so what's really being passed by value is the reference (a pointer) to the object.

The Autotype keyword is used to let a function be a little (not a lot) more forgiving about the types of the parameters that are passed into it. In the example here, the use of Autotype allows a function to accept integers or doubles (and strings of course):

Function Add(x, y : String) Autotype

Print(x + y)

End

Initialization

Add(1, 2)

End

An autotyped function with a MidiMessage parameter will accept calls with specific kinds of messages such as NoteMessage or ControlChangeMessage.

Functions can optionally return a value in which case the Returns clause must be present. If the Returns clause is present, then a variable called result exists in the function scope and whatever is assigned to that variable will be the return value.

There is deliberately no mechanism to return from the middle of a function.

Example:

Function SumNumbers(a,b,c : integer) returns integer

result = a + b + c

End

Function PlayMajorChord(keyboard : MidiInBlock, root : NoteMessage)

SendNow(keyboard, root) // Original note

SendNow(keyboard, Transpose(root, 4)) // The third

SendNow(keyboard, Transpose(root, 7)) // The fifth

End