EPL Programming Elements
This chapter describes the basic elements of EPL.
EPL Naming Rule
In the source code of an EPL application, whatever variable/function/data type etc, their name must start from english character and without non-english or non-number character in it.
EPL supports unlimited length name, and the name will never conflict to EPL language keywords due to EPL is an command-base language, such as ”If”, “While” those are all commands (functions).
Data Types
EPL data types are classified by System-Basic data type, Library-Defined data type and User-Defined data type.
System-Basic Data Type
| Data Type | Description |
|---|---|
| Byte | Contains an integer value between 0 to 255. 1 byte size (8 bits). |
| Short | Contains an integer value between -32768 to 32767. 2 bytes size (16 bits). |
| Integer | Contains an integer value between -2147483648 to 2147483647. 4 bytes size (32 bits). |
| Int64 | Contains an integer value between -9223372036854775808 to 9223372036854775807. 8 bytes size (64bits). |
| Float | Contains a floating point value between 3.4E-38 to 3.4E38. 4 bytes size (32 bits). |
| Double | Contains a floating point value between 1.7E-308 to 1.7E308. 8 bytes size (64 bits). |
| Boolean | Contains a value to indicate True or False. 2 bytes size (16 bits) |
| DateTime | Records date and time. 8 bytes size (64 bits). |
| String | A character string terminated with 0. Stores text data. |
| Bin | A data section in binary format. The Bin and Byte Array convert between from each other. The difference between Bin and Byte Array is Bin can change length automatically or manually, but Byte Array can only change length manually. |
| FunctionAddress | A pointer to a function to indicate function's address. 4 bytes size (32 bits). This data type is only valid in Dll command parameter. |
Byte/Short/Integer/Int64/Float/Double can be named as "Number", converting between each number type is possible.
Number: converting may possibly lose data precision.
All data type only be valid in internal EPL system, matches all supported data types
Library-Defined Data Type
Library-Defined data type is provided by EPL internal library, it can be used directly in EPL, just like system basic data type
User-Defined Data Type
You can freely to define your own data type (User-Defined Data Type), the data type can contain System-Basic Data Type and Library-Defined Data Type. To add a new user-defined data type, just click “Insert” -> “Data Type” menu.
Constants
EPL supports constants to store & express constant value that won’t be changed when the application is running. The data type of constant value can be Number, String, Boolean and DataTime. To define a new constant, just click “Insert” ->”Constant menu”. To use a constant value, plus a “#” mark before the constant name in source code. Such as: “#Pi” to instead of number “3.1415926535”.
Variable
EPL Variable has three different Operating-Domains, they are Global, Module and Local. The Global Variable can be used in any code-able place, the Module Variable can be used in any code-able place of a module, and the Local Variable can be used in any code-able place of its contained function.
The variable also can be static type as usual. Unstatic Variable in EPL can be initialized automatically. To evaluate a variable, just use a “=” operator or “Set” function.
EPL also supports Variable Array, to use array just use mark “[][]” to specify the element index of an array.
Operator
Using operator in EPL, there are two ways, using operator or using command (function) name to instead, because EPL is a command-based programming language. The following lists all the operator of EPL. Notice that, smaller priority number for higher priority
| Operator | Priority | Command Name | Description |
|---|---|---|---|
| - | 1 | Neg | Returns the negative value of a numeric value |
| * | 2 | Mul | Returns the product of two numeric values |
| / | 2 | Div | Returns the quotient of two numeric values |
| \ | 3 | DivE | Returns the integer part of the quotient of two numeric values |
| % | 4 | Mod | Returns the remainder of two numeric values |
| + | 5 | Add | 1, Returns the sum of two numbers; 2, Concatenates two String and return the result; 3,Concatenates two Bin and returns the result |
| - | 5 | Sub | Returns the difference between two numeric values |
| <> | 6 | Unequal | Returns True if the "Value1" is not equal to "Value2", otherwise returns False |
| = | 6 | Equal | Returns True if the "Value1" is equal to "Value2", otherwise returns False |
| < | 6 | Less | Returns True if "Value1" is less than "Value2", otherwise returns False |
| > | 6 | Greater | Returns True if "Value1" is greater than "Value2", otherwise returns False |
| <= | 6 | LessEqual | Returns True if "Value1" is less than or equal to "Value2", otherwise returns False |
| >= | 6 | GreaterEqual | Returns True if "Value1" is greater than or equal to "Value2", otherwise returns False |
| && | 7 | And | Returns True if the two parameters are both True, otherwise returns False. |
| || | 8 | Or | Returns True if any one of the two parameters is True, otherwise returns False |
| = | 9 | Set | Value assignment |
Function
For user-defined functions, it is very often to use by developer, the EPL function represents very flexible & powerful way to write your own-defined functions.
The EPL Function Parameter can be passed by reference, also can be optional and with a default value setting. To pass variable array is also be allowed.
To exit your function and return a value, just call "Return(YourReturnValue)” function.
Flow Control
To control the flow of EPL source code, it is by commands that list below.
| Command Name | Description | Picture |
|---|---|---|
| If | Determines the executing flow according to the condition. The routine will execute ordinally if the parameter is True, otherwise the routine will jump to the code pointed by the left arrow |  |
| IfTrue | Determines the executing flow according to Boolean parameter. The routine will execute ordinally if the parameter is True, otherwise the routine will jump to the code that pointed by the left arrow. Notice: This function has no "False" part, that's different like "If" function |  |
| Case | Determines the executing flow according to the Boolean parameter. The routine will execute ordinally if the parameter is True, otherwise the routine will jump to the next branch of "Case" to determine | |
| Do | Enters the loop | None |
| For | Repeats the loop body that between "For" and corresponding "Next". Initializes "LoopVar" by "StartingValue" when executes this command first time. Determines whether the "LoopVar" is greater than "EndingValue" when executes to this command every time, exits the loop body to executes the statement after the corresponding "Next" if True, otherwise continues the loop |  |
| Continue | Jumps to the ending of the current loop body immediately | None |
| Break | Exits the current loop body immediately to execute the statement after current loop | None |
| Return | Stops the execution of a function and returns control to the calling function. A return statement can also returns a value to the calling function | None |
| End | Stops current running EPL program | None |
Form
Under windows, EPL provides very rich & powerful form programming elements than ever. Form in EPL is like an object, contains Method, Property and Event. All the necessary & basic function is supported. Without that, EPL provides a very rich form shape effects.
The following describes Form in details.
EPL 4.0 Form Properties List
| Property Name | Description |
|---|---|
| Left | Specifies the location of the left edge of the form |
| Top | Specifies the location of the top edge of the form |
| Width | Specifies the width of form, in pixels units |
| Height | Specifies the height of form, in pixels units |
| Tag | Specifies extra string type value for form or program |
| Visible | Specifies the visibility of a form |
| Disable | Specifies whether the form is disabled |
| MousePointer | Specifies the mouse pointer for the form |
| Caption | Specifies caption for the form |
| Border | Specifies the type of the form border |
| BackColor | Specifies background color for form |
| Picture | Specifies the background picture for form displaying |
| PictureMode | Specifies the displaying style if there's background picture |
| BackMusic | Specifies the music for playing when the form is loaded |
| RepeatTime | Specifies how many times the back music will be played |
| ControlButtons | Specifies whether display all the control button and menu |
| MaxButton | Specifies whether display maximize button and restore button |
| MinButton | Specifies whether display minimize button |
| Position | Sets the position and state of the form |
| Moveable | Specifies whether the form can move |
| EnterFocusDown | If this property is True, the focus will be moved to next control when Enter key is press on the form. If this property is False, the Enter key refers to the default button |
| EscToClose | Specifies whether allow user to use Esc key to close form |
| F1ToHelp | Specifies whether user can press F1 to open the help-information about this form |
| HelpFileName | The help file name. If this is not specified, the default help file name(exe file name, exclude suffix, + .hlp) is used |
| HelpContext | Specifies the help tag |
| InTaskBar | Specifies whether the window showed in the windows task |
| FreeMove | Sets whether the form can be drag when left mouse button is down at any position of the form. If this property is True, all the controls in the form that cannot have focus does not received "LButtonDown" and "LButtonUp" event |
| FormShape | Specifies form shape for looking |
| AlwasyOnTop | Specifies whether the form is always on the top of any other forms |
| TitleBarActive | Specifies this property to be True if you wish the title bar always be active |
EPL 4.0 Form Methods List
| Method Name | Description |
|---|---|
| GetHWnd | Returns a handle to a form or a control, the handle is just Win32 HWND |
| Destroy | Destroys this form and all controls on this from. Loads the form again to use if the form has been destroyed |
| SetFocus | Moves the focus to this form or control. For a form, the focus will move to the first control that can accept focus |
| HasFocus | Indicates whether the control has the focus |
| GetClientWidth | Returns the width of client area, in pixels units. For a form, the client area is the entire area of the window excludes title bar, menu bar, frames. For a control, its client area is equal to its entire area |
| GetClientHeight | Returns the height of client area, in pixels units. For a form, the client area is the entire area of the window excludes title bar, menu bar, frames. For a control, its client area is equal to its entire area |
| DisableRedraw | Disables the redraw operation of a Form or control to avoid flicker. "EnableRedraw" can be called to resume |
| Redraw | Notifies the Windows system that the entire area of this Form or Control need to be redrawed |
| RedrawRect | Notifies the Windows system that the specified rectangle of this Form or Control needs to be redrawed |
| CancelRedraw | Notifies the Windows system that this Form or Control does not need to be redrawn, all its display content will be reserved |
| Refresh | Redraws if displaying content of this from or control need to redraw, otherwise returns immediately |
| Move | Changes the position or size of a Form or Control |
| Zorder | Changes the layer of a Form or Control |
| PopupMenu | Displays the menu at the specified position or the current mouse position. Automatically use its container form if called object is window control |
| SendMessage | Sends the specified message to a window or control. It calls the window procedure for the specified window and does not returns until the window procedure has processed the message |
| PostMessage | Places (posts) a message in the message queue associated with the thread that created the specified window and returns without waiting for the thread to process the message |
| GetTagControl | Returns the control that contains the specified numerical string in the current Window Form. An runtime occurs if doesn't exist |
| SetShapePicture | Sets the shape of the form with the picture, Note: the picture format can't be icon or cursor. The contour of the picture should be as solid as possible, that can make the refreshing speed of the Window Form faster. Returns True if succeeds, otherwise returns False |
| Activate | Activate a form |
| SetTrayIcon | Sets an icon that indicated this program to system tray |
| PopupTrayMenu | Pops up menu in the current mouse position, this function is for popuping system tray icon menu |
| SetParent | Sets specified form or form control as parent form of this object |
EPL 4.0 Form Events List
“System Basic-Events” & “Control Self-Events”
“System Basic-Events” is provided by the system, all form controls has these events. In list below will mark as type of “Basic”.
“Control Self-Events” is provided by specified control itself. In list below will mark as type of “Self”.
| Events Name | Events Name | Type |
|---|---|---|
| LButtonDown | Occurs this event when the user presses the left mouse button while the cursor is on the form | Basic |
| LButtonUp | Occurs this event when the user releases the left mouse button while the cursor is on the form | Basic |
| DblClick | Occurs when the user presses and releases a mouse button and then presses and releases it again on the form | Basic |
| RButtonDown | Occur this event when the user presses the right mouse button while the cursor is on the form | Basic |
| RButtonUp | Occurs this event when the user releases the right mouse button while the cursor is on the form | Basic |
| MouseMove | Occurs when the user moves the mouse on the form | Basic |
| GetFocus | Occurs this event when object got inputting focus | Basic |
| LostFocus | Occurs this event when the object losts the focus | Basic |
| KeyDown | Occurs this event when user presses a key | Basic |
| KeyUp | Occurs this event when the user releases a key that previously pressed | Basic |
| KeyPress | Occurs this event when user presses or releases a character key | Basic |
| MouseWheel | Occurs this event when user scrolls mouse wheel | Basic |
| AfterCreate | Occurs this event when all the controls has been created before displaying | Self |
| BeforeClose | Occurs this event before close the form. Returns False if doesn't allow to close, returns True or returns nothing if allow to close | Self |
| BeforeDestroy | Occurs this event before destroy this window. All the controls will be disable after destroy | Self |
| Move | Occurs this event when the position of window has been changed | Self |
| Size | Occurs this event when the size of form has been changed | Self |
| Activate | Occurs this event when the state of the window has been change to be active | Self |
| Deactivate | Occurs this event when the state of the window has been change to be deactivated | Self |
| Idle | Occurs this event when system is in idle state, user can do some processing for background. Returns False or returns nothing to disable this event to occur again. Returns True to enable to occur this event again | Self |
| FirstActivate | Occurs this event when first time to be active | Self |
| TrayEvent | Occurs this event when the try icon set by this form received mouse click event | Self |
| Show | Occurs this event when the form is displayed | Self |
| Hide | Occurs this event when hide form | Self |
EPL form also provides several very easy ways for you to create outstanding form with amazing effect. To set these effects only cost few steps, such as insert a picture, and change a property, even without write any code.
Module
The EPL Module is a form codes and functions container. For each form, its codes is all in a module, such as “FormModuleN”. For functions, module can stores them in it, and name a meaningful module name for represent a serials of functions.
Class
EPL is an OOP supported development environment, EPL Class is implemented of EPL-OOP. For details about EPL Class, please see Object-Oriented Programming chapter.
Resource
EPL Resource is for you to store and use binary data such as picture, sound and any binary file, the data type of resource is Bin.