When using a function in a formula, type the name of the function and supply the arguments required. For example, the Length function requires a String argument and computes the length of the string.
Local StringVar x := "hello"; Length (x) //The formula returns the Number 5
Supplying arguments of the incorrect type required by the function produces an error. For example, calling Length (3) would produce an error since Length does not accept a Number argument.
Functions sometimes can accept different numbers of arguments or types of arguments. For example, the CDate function which could accept a single String argument to form a Date value or three Number values holding the year, month and day respectively and form a Date value from them. See Date, Time, and DateTime.
Example with the Mid function
Local StringVar x := "hello"; Local StringVar y; //Start at position 2, go to the end of the string y := Mid (x, 2); //y is now "ello" //Start at position 2, extract 1 character y := Mid (x, 2, 1) //y is now "e"
These classes of functions are: Math, Summary, Financial, String, Date/Time, Date Range, Array, Type Conversion, Programming Shortcuts, Evaluation Time, Print State, Document Properties and Additional Functions. There are also some functions specific to conditional formatting formulas.