Difference between revisions of "EDT:Language Overview"

Latest revision as of 10:41, 10 July 2012

This overview introduces the EGL language as defined in EGL Core and as extended by Eclipse IDE for the EGL Web Developer. Reference details are in the EDT help system, which is made available when you install a download from the following site: www.eclipse.org/edt/download/.

In many ways, EGL is like other programming languages. It includes familiar constructs such as loops and transfers of control. It is built on a set of types, each of which defines the operations that are available for each value of the type. Last, it involves a process for validating source code and for converting the source code into a less abstract form, closer to the runtime need.

EGL is special in its reliance on stereotypes, which are declarations used by the software that transforms the source code to another form such as Java or JavaScript.

Stereotypes offer simplicity. First, they ensure that the output created for a source-code element such as "Handler" includes details for a particular use; for example, to be runnable on a full-page web browser. The developer who writes a custom Handler element and declares the appropriate stereotype does not need to know a lot about a browser to write the code. He can rely on the pre-tested logic that is created by an EGL JavaScript generator. The pre-tested logic supplements the custom logic.

Second, stereotypes provide a way to extend the language. The creation of a new kind of stereotype enables an existing source-code element to have an alternative use. For example, a future stereotype might allow a developer to write a custom Handler element and then to create output for a mobile device that runs under the Android operating system. This alternative option requires that the extender create Java classes that add to the existing generator logic.

The mechanism for using stereotypes is provided by EGL Core, which includes the basic rules of EGL syntax. Most stereotypes are provided by an EGL extension, and the first extension is Eclipse IDE for the EGL Developer.

We describe stereotypes in the first of the following pages and proceed to other aspects of the language:

@@ Line 1: / Line 1: @@
-= Introduction  =
+<span style="font-size:smaller;">&lt;&nbsp;[[EDT| EDT wiki home]]</span>
-This essay gives an overview of the EGL language.&nbsp;
+This overview introduces the EGL language as&nbsp;defined&nbsp;in EGL Core and as extended&nbsp;by Eclipse IDE for the EGL Web Developer.&nbsp;Reference details are in the EDT help system, which is made available when you install a download from the following site:&nbsp; [http://www.eclipse.org/edt/download/ www.eclipse.org/edt/download/].
-== Types and values  ==
+In many ways, EGL is like other programming languages. It includes familiar constructs such as loops and transfers of control. It is built on a set of '''types''', each of which defines the operations that are available for each value of the type. Last, it involves a process for validating source code and for converting the source code into a less abstract form, closer to the runtime need.
-In general usage, a '''type''' such as integer or string defines a set of values and a set of operations that can be applied to those values. For example, integers are whole numbers that can be added, subtracted, and so forth; and the number 5 is a value of that type.
+EGL is special in its reliance on '''stereotypes''', which are declarations used by the software that&nbsp;transforms the source code to another form such as Java or JavaScript.
-The meaning is much the same in programming, where every value is “of a type.” The type defines the structure of the value and the set of operations that can be applied to the value.
+Stereotypes&nbsp;offer simplicity. First,&nbsp;they ensure&nbsp;that the&nbsp;output&nbsp;created for a&nbsp;source-code&nbsp;element such as&nbsp;"Handler" includes details for a particular use;&nbsp;for example, to be runnable on a&nbsp;full-page web browser.&nbsp;The developer who&nbsp;writes a custom Handler element and declares the appropriate&nbsp;stereotype does not need to know a lot about a browser to write&nbsp;the code. He can rely on&nbsp;the pre-tested logic that is created by an EGL JavaScript generator.&nbsp;The pre-tested&nbsp;logic&nbsp;supplements the custom logic.&nbsp;&nbsp;&nbsp;
-=== Reference and value types  ===
+Second, stereotypes provide a way to extend the language.&nbsp;The creation of a&nbsp;new kind of stereotype&nbsp;enables an existing source-code element&nbsp;to have an&nbsp;alternative use. For example, a&nbsp;future stereotype might allow a developer to write a custom Handler element and then to&nbsp;create output for a mobile device that&nbsp;runs under&nbsp;the Android operating system. This alternative&nbsp;option requires that the extender&nbsp;create Java classes that&nbsp;add to the&nbsp;existing generator logic.&nbsp;
-In general, types are of two kinds, reference and value:
+The mechanism for using stereotypes is provided by&nbsp;EGL Core, which includes the&nbsp;basic rules of EGL syntax.&nbsp;Most stereotypes are provided by an EGL extension, and the first extension is Eclipse IDE for the EGL&nbsp;Developer.<br>
-*A '''reference type''' defines an '''object''', which is a value in a memory area that was allocated specifically to hold&nbsp;the value. The object is referenced from some logic and is an instance of the type. In this case, the words "value," "object," and "instance" are interchangeable.
+We describe stereotypes in the&nbsp;first of&nbsp;the following pages and&nbsp;proceed to&nbsp;other aspects of the language:&nbsp;<br>
-*A '''value type '''defines a value that is embedded in an object rather than being referenced from it.
-In general, a '''field declaration''' is a coded statement that has two effects: <br>
+*[[EDT:Language Overview02|EGL types and values]]
+*[[EDT:Language Overview03|Packages and type-name resolution]]
+*[[EDT:Language Overview04|Syntax and scope]]
-*Declares a value of a type.
+<br> <br>
-*Names a memory area that provides access to the value. If the value is based on a reference type, the memory area holds an address or other detail that points to the value. If the value is based on a value type, the memory area contains the value itself.
-Turning now to the syntax of EGL, here are two field declarations:<br>
+&nbsp;
-<pre>&nbsp;&nbsp;&nbsp;// variable declaration
-&nbsp;&nbsp; NumberOfCars INT;&nbsp;&nbsp;&nbsp;&nbsp;
-&nbsp;&nbsp;
-&nbsp;&nbsp; // constant declaration
-&nbsp;&nbsp; const MINIMUMNUMBER INT = 2; </pre>
-The type is each case is INT, which is a value type for four-byte integers. The first statement declares a '''value variable''', the second declares a '''value constant'''.
-For a second example, you might declare a list of five integers by coding a statement like one of these:<br>
+&nbsp;
-<pre>   // variable declaration
-   NumberOfVehicles INT[5];
-   // constant declaration
+[[Category:EDT]]
-   const MINIMUMNUMBERS INT[5] = [1,2,3,4,5];</pre>
-The type in this case is INT List or INT[], which is a reference type. The first statement declares a reference variable, which means that you can assign a different list to <code>NumberOfVehicles</code> in a later assignment. Incidentally, you can also change the values inside the list and can change the number of elements.
-The second statement declares a reference constant, which means that you cannot assign a different list to <code>MINIMUMNUMBERS</code> in a later assignment. However, even in this case, you can alter the values inside the list and can change the number of elements.
-The behavior is consistent because each declaration in the second example identifies a memory area that contains an address of a second memory area. The constant is only constant in the sense that the area identified as <code>MINIMUMNUMBERS</code> must always contain the same address, which refers to the same list. The following, subsequent assignment is not valid even though the values are the same:<br>
-<pre>   // An invalid assignment
-   MINIMUMNUMBERS = [1,2,3,4,5]; </pre>

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Difference between revisions of "EDT:Language Overview"

Latest revision as of 10:41, 10 July 2012