Paradox KB: OPAL: Language Basics Topic

If you've never programmed in ObjectPAL, spend 10 minutes and see how easy it is to program Paradox for Windows.

This detailed ObjectPAL primer will get you up and running developing in Paradox/ObjectPAL within a few hours.

Part 3.

Before you code in ObjectPAL, ask yourself two questions. Does Paradox already do this? Is there a better and easier way? Remember, simple solutions for simple problems.

If, in experimentation, you use sleep(), doDefault, or DisableDefault to overcome some odd or misunderstood behavior, do not leave the commands in your code. If using the command didnt seem to make a difference, then take it out. Use commands only when they are called for. One great way to really learn the event model and the power of these and other commands is to experiment with adding them. Remember to take them out, however, if they do not do what you wanted.

Think levels when you code in the Pardox ObjectPAL development environment.

The syntax of object.method() is consistent throughout ObjectPAL. If an object with the name box has code on its mouseClick event, you can access that code with box.mouseClick() method from any other object. When this code executes, the UIObject method mouseClick() calls the mouseClick event.

How do you know when you can call the code in a built-in method of an object? Easy, if the run-time library has a method equivalent, then you can use itfor example, mouseClick() and pushButton().

ObjectPAL uses = for it's assignment operator.

ObjectPAL is not case sensitive. My preference for ObjectPAL is to follow the camel casing promoted in the examples and help files originally developed by Borland.

ObjectPAL code blocks are surrounded by statement ending keywords that all use End with camel caps such as endMethod, endVar, endIf, endSwitch, and endTry.

Commenting Code
ObjectPAL uses ; for a single line comment and { } for a multiple line comment.

Common comparison operators:

In ObjectPAL, you declare one or more constant values within a const..endConst block. Optionally, you can specify the dataType by casting the value as part of the declaration. If you do not specify the data type, the data type is inferred from the value as either a LongInt, a Number, a SmallInt, or a String. As with variables, the const..endConst block can come within a method or procedure as the first bit of code, or in the Const window. Putting it above the method or procedure is allowed but has no significance so don't.

Corel Paradox for Windows (was Borland Paradox). Also, Borland used to offer a Paradox for DOS tool which support it's Paradox Application Language (PAL) which is not compatible with ObjectPAL. The biggest drawback to Paradox is that Corel does not have anyone at Corel actively developing Paradox for Windows (as opposed to Microsoft Access which does).

In ObjectPAL, you use Cursor.InsertRecord to add a new record, Cursor.postRecord to post the record, and Cursor.deleteRecord() to delete it. To edit a record, you must put the cursor into edit mode, Cursor.Edit(). (A cursor applies to both a TCursor and UIObject.)

ObjectPAL gives you tremendous flexibility with editing data and includes many additional commands such as insertAfterRecord and isEdit. For dBASE tables, you can also use unDeleteRecord() to un-delete a record. See the ObjectPAL help for more commands.

In ObjectPAL, an empty variable can be unassigned (essentially null) or blank (equivalent to ""). You have to use both isBlank and isAssigned to check for an empty string.

Languages Focus: End of Statement

In coding languages, common End of statement specifiers include a semicolon and return (others exist too). Also of concern when studying a language is can you put two statements on a single code line and can you break a single statement into two or more code lines.

ObjectPAL supports a simple If...Else...EndIf statement.

Notice ObjectPAL does not support an ElseIf feature as part of an if statement. Instead use a switch statement

Literals are quoted as in "Prestwood".  If you need to embed a quote use a slash in front of the quote as in \". 

In ObjectPAL, string literals are limited to 255 characters but there's nothing preventing you from using multiple string literals together as in:

ObjectPAL logical operators:

String literals s are limited to 255 characters but you can simply add two strings together as in:

The ObjectPAL unary operators are:

Declaring variables is optional unless you click Program | Compiler Warnings while in the ObjectPAL editor for every form, script, and library you create. Using Compiler Warnings is strongly recommended to avoid incorrectly typing an existing variable and to avoid any confusion about variable scope. Also recommended is turning on Compile with Debug for every form, script, and library too for tighter, cleaner code.

Undeclared variables are AnyType variables. Common data types include Currency, Date, Datetime, Logical, LongInt, Number, SmallInt, String, and Time.

Declare local variables within a method. If you want a local static variable (retains it's value because it is not destroyed), declare the varialbes above the method. Variables declared in an object's Var window are visible to all methods attached to that object, and objects that it contains.

Paradox provides experts that generate code at the field level, in the form open, etc. It is a good idea to study the ObjectPAL generated by these experts.