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Front End Functions

Summary:

• Basics
• The frontCall method
• Standard built-in front end functions

See also: Interface built-in class

Basics

The BDL language provides a specific method to call functions defined in the front end that will be executed locally on the workstation where the front end resides. When you call a user function from BDL, you specify a module name and a function name. Input and output parameters can be passed/returned in order to transmit/receive values to/from the front end. A typical example is an "open file" dialog window that allows you to select a file from the front end workstation file system.

A set of standard front end functions is built-in by default in the front end. It is possible to write your own functions in order to extend the front end possibilities. For example, you can write a set of functions to wrap an existing API, such as Window DDE or OLE. A set of user functions is defined in a module, implemented as a Windows DLL or UNIX shared library. These modules are loaded automatically according to the module name. See the front end documentation for more details about creating user function modules in the front end.

The frontCall method

Purpose:

The Interface built-in class provides a special method to perform front end calls.

Syntax:

Notes:

1. module is a string defining the name of the module (DLL or shared lib) where the function is defined. When you specify "standard", it references built-in functions provided by default by the front end.
2. function is a string defining the name of the function to be called.
3. parameter-list is a list of input parameters.
4. returning-list is a list of output parameters.

Usage:

Module and function names are case-sensitive.

Input and output parameters are provided as a variable list of parameters, with the square braces notation ([param1,param2,...]). Input parameters can be an expression supported by the language, while all output parameters must be variables only, to receive the returning values. An empty list is specified with [].

Errors:

If the function could not be executed properly, one of the following exceptions might occur:

Example:

01 MAIN
02   DEFINE data STRING
03   CALL ui.Interface.frontCall( "mymodule", "connect", ["client1",128], [] )
04   LET data = "Hello!"
05   CALL ui.Interface.frontCall( "mymodule", "send", [data, data.getLength()], [] )
06   CALL ui.Interface.frontCall( "mymodule", "receive", [], [data] )
07   DISPLAY data
08   CALL ui.Interface.frontCall( "mymodule", "disconnect", ["client1"], [] )
09 END MAIN

Standard built-in front end functions

The following table shows the built-in functions implemented by the front ends in the "standard" module. Note that most of these functions are supported by desktop front-ends (GDC/GJC) only.

Warning: Additional modules and functions are available for front-ends, but are specific to the front-end type. Please refer to the front-end documentation for more details.