An exported function must be a niladic or monadic defined function (dfns and derived functions are not allowed) and may optionally return a result. Ambivalent functions (functions with optional left argument) are allowed, but will be called monadically by the host application.

COM syntax differs from APL syntax in many ways and the SetFnInfo method is required to declare an APL function to COM in terms that COM understands. In particular, although monadic APL functions take just one argument, COM functions may take several parameters, and some may be optional.

A function exported by SetFnInfo will be called by a host application with the number of parameters that SetFnInfo has described. The argument received when the function is called by a host application, will be a nested vector of this length.

Function info

This specifies an optional help string which describes what the function does, the data type of the result (if any) and the names and data types of its arguments.

If the function syntax is fully described, each element of Function Info is a 2-element vector of character vectors. The first element contains the help string and the COM data type of the function's result. Subsequent elements contain the name and COM data type of each parameter.

However, both the help string and the names of the parameters are optional and may be omitted. If so, one or more elements of Function Info may be a simple character vector.

Consider a very basic function ADD in an ActiveXControl called F.dbase, that is designed to add a record to a personnel database. The database consists only of a list of names, ages and addresses.

Function ADD expects to be called with a name (character string), age (number) and address (character string), and returns a result 0 or 1 (Boolean) according to whether the record was successfully added. This function could be declared as follows:

      HELP←'Adds a new record to the personnel database'
      SPEC←⊂(HELP 'VT_BOOL')      ⍝ Result is Boolean     
      SPEC,←⊂('Name' 'VT_BSTR')   ⍝ 1st param called 'Name' is a string   
      SPEC,←⊂('Age' 'VT_I4')      ⍝ 2nd param called 'Age' is an integer  
      SPEC,←⊂('Address' 'VT_BSTR')⍝ 3rd param called 'Address' is a string

      F.dbase.SetFnInfo 'ADD' SPEC

Alternatively, but much less helpfully, the function could be declared to take a single unnamed nested argument, leaving it to the host application programmer to guess at its structure :

      SPEC←⊂('' 'VT_BOOL')              ⍝ No help string, result is Boolean
      SPEC,←⊂('' 'VT_ARRAY OF VT_VARIANT') ⍝ Param is a nested array
      F.dbase.SetFnInfo 'ADD'SPEC

In both these last two cases, the name of the property, which is totally independent of the name of the APL function, is given as Property name.

If omitted, the function type is method.