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ELENA is a general-purpose, object-oriented, polymorphic language with late binding. It features message dispatching/manipulation, dynamic object mutation, a script engine / interpreter and mix-ins. |
ELENA is a general-purpose, object-oriented, polymorphic language with late binding. It features message dispatching/manipulation, dynamic object mutation, a script engine / interpreter and mix-ins. |
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* ELENA on [https://github.com/ELENA-LANG/elena-lang/wiki/ Github] |
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== The simplest program == |
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To create a simple console program we have to declare the public **program** closure in the project root namespace: |
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public program() |
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{ |
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} |
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Everything in ELENA is an object. To interact with it we have to send a message. The message consists of *an action* and a *parameter list*. |
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The statement should be terminated by a semicolon. |
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public program() |
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{ |
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console.writeLine("Hello!"); |
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} |
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In our example the action is **writeLine** and the parameter list consists of a single string constant. The message target is **console** object (implementing input / output operations with a program console). |
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Several message operations can be done in a single statement: |
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public program() |
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{ |
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console.writeLine("Hello!").writeLine("How are you?"); |
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} |
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The result will be: |
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Hello! |
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How are you? |
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We may read a user input by sending **readLine** message without parameters: |
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public program() |
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{ |
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console.write("What is your name:").writeLine("Hello " + console.readLine()) |
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} |
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The result will be: |
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What is your name:Alex |
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Hello Alex |
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**Console::write** method is similar to **writeLine** except that it writes to the output screen without a new line character. |
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== Declaring a variable == |
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A variable can be declared in an assignment statement starting with **var** attribute: |
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var myVariable := "A text"; |
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where we declare a variable **myVariable** and initialize it with a string constant value. |
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The assigning value can be an expression itself: |
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public program() |
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{ |
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console.writeLine("Hello!").writeLine("How are you?"); |
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var s := console.readLine() |
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} |
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ELENA is a dynamic language and in most cases we may not specify the variable type: |
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public program() |
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{ |
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var s := "Hello"; |
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console.writeLine(s); |
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s := 2; |
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console.writeLine(s); |
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} |
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The output will be: |
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Hello |
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2 |
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But it is possible to specify the variable expected type: |
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String s := "Hello"; |
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console.writeLine(s); |
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*where system'String is a class representing text as a sequence of UTF-8 characters.* |
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We may use a class alias to simplify the code: |
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string s := "Hello"; // string is a String class alias |
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console.writeLine(s); |
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ELENA does not enforce types in compilation-time, so the following code will be successfully compiled: |
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string s := "Hello"; |
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s := 2; |
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But it will raise an exception in the run-time: |
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system'IntNumber : Method #cast[0] not found |
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Call stack: |
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system'Exception#class.new[1]:exceptions.l(125) |
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system'MethodNotFoundException#class.new[2]:exceptions.l(236) |
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system'$inlineC.start[0]:win32_app.l(313) |
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mytest'program.#invoke[0]:test.l(5) |
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system'$inlineC.start[0]:win32_app.l(39) |
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system'#startUp:win32_app.l(52) |
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As you may see, the compiler injects the typecasting code, so the actual code looks like this: |
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string s := "Hello"; |
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s := cast string(2); |
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*where* **cast string(2)** *is a construction to typecast the target expression* - **a numeric constant** - *to the expected type* - **System'String** |
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As a result if the object supports casting method the operation will work. For example, system'IntNumber can be implicitly converted into system'RealNumber so the following code: |
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public program() |
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{ |
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real r := 2; |
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console.writeLine(r) |
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} |
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will be successfully executed with the result: |
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2.0 |
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== Basic Types == |
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=== The Boolean Type === |
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Boolean type is used in conditional operations and may accept only two Boolean literals - **true** and **false**. |
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import extensions; |
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public program() |
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{ |
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bool b1 := true; |
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bool b2 := false; |
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console.printLine(b1,"==",b1," is ",b1==b1); |
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console.printLine(b2,"==",b2," is ",b2==b2); |
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console.printLine(b1,"==",b2," is ",b1==b2); |
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console.printLine(b2,"==",b1," is ",b1==b2); |
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} |
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*Note that implicit extension method - **extensions'outputOp.printLine[]** - was used to simplify the output operations.* |
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The output is: |
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true==true is true |
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false==false is true |
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true==false is false |
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false==true is false |
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=== The Numeric types === |
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The most used numeric types in ELENA are 32-bit signed integer number (represented by **IntNumber**), 64-bit signed integer number (represented by **LongNumber**) and 64-bit floating-point number (represented by **RealNumber**): |
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import extensions; |
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public program() |
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{ |
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int n := -234; |
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long l := 1235456765l; |
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real r := 2.3456r; |
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console.printLine("Integer number - ",n); |
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console.printLine("Long integer number - ",l); |
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console.printLine("Real number - ",r) |
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} |
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The output is: |
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Integer number - -234 |
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Long integer number - 1235456765 |
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Real number - 2.3456 |
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=== The String Type === |
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**String** is used to store the text encoded in UTF-8. String is a read-only collection of **CharValue** classes each representing UTF-32 symbol. *Note that one character may be encoded with more than one byte!*. |
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import extensions; |
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public program() |
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{ |
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var s := "Hello"; |
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console.printLine("The first character of ",s," is ", s[0]); |
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console.printLine("The last character of ",s," is ", s[s.Length - 1]) |
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} |
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The output is: |
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The first character of Hello is H |
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The last character of Hello is o |
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The same code for example with a Russian text will not work. Because every character is encoded with a two bytes and this should be taken into account. |
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import extensions; |
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public program() |
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{ |
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var s := "Привет"; |
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console.printLine("The first character of ",s," is ", s[0]); |
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console.printLine("The last character of ",s," is ", s[s.Length - 1]) |
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} |
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The output is: |
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The first character of Привет is П |
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An index is out of range |
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Call stack: |
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system'Exception#class.new[1]:exceptions.l(125) |
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system'OutOfRangeException#class.new[1]:exceptions.l(156) |
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system'OutOfRangeException#class.new[0]:exceptions.l(156) |
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system'String.at[1]:memory.l(1243) |
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mytest'program.#invoke[0]:test.l(8) |
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system'$inlineC.start[0]:win32_app.l(39) |
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system'#startUp:win32_app.l(52) |
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We may use another class representing UTF-16 text (**WideString**) to solve this problem: |
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import extensions; |
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public program() |
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{ |
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var s := "Привет"w. // UTF-16 string |
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console.printLine("The first character of ",s," is ", s[0]); |
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console.printLine("The last character of ",s," is ", s[s.Length - 1]); |
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} |
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The output will be correct this time: |
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The first character of Привет is П |
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The last character of Привет is т |
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But this code will not work with Chinese text or any other requiring more than 2 bytes per symbol. So instead we may use enumerators: |
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import system'routines; |
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import extensions; |
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public program() |
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{ |
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var s := "Привет"; |
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console.printLine("The first character of ",s," is ", s.FirstMember); |
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console.printLine("The last character of ",s," is ", s.LastMember) |
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} |
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The output will be correct for any UTF-8 text: |
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The first character of Привет is П |
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The last character of Привет is т |
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=== Array types === |
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It is possible to declare a generic (_system'Array_) or strong-typed template-based (_system'Array#1_) array. |
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import extensions; |
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public program() |
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{ |
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var strongTypedArray := new int[] {1,2,3}; |
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var genericArray := Array.allocate(3); |
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genericArray[0] := 1; |
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genericArray[1] := "b"; |
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genericArray[2] := 2.3r; |
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console.printLine("strong-typed array ",strongTypedArray.asEnumerable()); |
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console.printLine("dynamic-typed array ",genericArray.asEnumerable()); |
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} |
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The output is: |
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strong-typed array 1,2,3 |
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dynamic-typed array 1,b,2.3 |
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== Basic arithmetic operations == |
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ELENA supports basic arithmetic operations with integer and floating-point numbers: |
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import extensions; |
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public program() |
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{ |
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var n1 := 12; |
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var n2 := 5; |
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var n3 := -3; |
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var r1 := 2.3r; |
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console.printLine(n1, " + ", n2, " = ", n1 + n2); |
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console.printLine(n1, " - ", n2, " = ", n1 - n2); |
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console.printLine(n1, " * ", n3, " = ", n1 * n3); |
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console.printLine(n1, " / ", n2, " = ", n1 / n2); |
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console.printLine(n1, " + ", n2, " * ", r1 ," = ", n1 + n2 * r1) |
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} |
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The result is: |
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12 + 5 = 17 |
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12 - 5 = 7 |
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12 * -3 = -36 |
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12 / 5 = 2 |
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12 + 5 * 2.3 = 23.5 |
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== ?? operator == |
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Operator ?? is used to deal with nil. |
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_a ?? b_ - will return _a_ if _a_ is not _nil_ or _b_ |
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See the following code: |
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import extensions; |
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public program() |
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{ |
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var a := nil; |
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var b := a ?? 0 + 2; |
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console.printLine(a ?? "nil", " ?? 0 + 2 = ", b); |
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a := 1; |
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b := a ?? 0 + 2; |
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console.printLine(a ?? "nil", " ?? 0 + 2 = ", b); |
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} |
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The output is: |
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nil ?? 0 + 2 = 2 |
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1 ?? 0 + 2 = 3 |
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The operator can be used for typecasting operations as well: |
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_cast type(a) ?? b_ - will typecast _a_ to _type_ or return _b_ if it is not possible. |
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See the code: |
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import extensions; |
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public program() |
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{ |
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string s := "a"; |
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var n := 2; |
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console.printLine("cast int(",s,") ?? 0 = ", cast int(s) ?? 0); |
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console.printLine("cast int(",n,") ?? 0 = ", cast int(n) ?? 0); |
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} |
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The output is: |
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cast int(a) ?? 0 = 0 |
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cast int(2) ?? 0 = 2 |
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== Conditions, Multi-select, Loops == |
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Conditional statement in ELENA are defined as follows: |
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if(<Boolean expression>) |
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{ |
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/* doSomething if TRUE*/ |
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} |
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else |
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{ |
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/*doSomehting if ELSE*/ |
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}; |
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We could omit else part |
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if(<Boolean expression>) |
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{ /*doSomehting if TRUE*/ }; |
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Usually Boolean expression is a result of a comparison operation: |
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public program() |
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{ |
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console.writeLine("Hello!").writeLine("How are you?"); |
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var s := console.readLine(); |
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if(s == "good") |
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{ |
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console.writeLine("Me too") |
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} |
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else |
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{ |
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console.writeLine("What happends?") |
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} |
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} |
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Several conditions can be checked: |
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public program() |
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{ |
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console.writeLine("Hello!").writeLine("How are you?"); |
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var s := console.readLine(); |
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if((s == "good") || (s == "fine")) |
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{ |
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console.writeLine("Me too") |
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} |
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else |
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{ |
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console.writeLine("What happends?") |
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} |
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} |
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A switch statement can be implemented using => operator: |
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public program() |
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{ |
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console.writeLine("Hello!").writeLine("How are you?"); |
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var s := console.readLine(); |
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s => |
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"good" { console.writeLine("Me too") } |
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"fine" { console.writeLine("Glad to hear") } |
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"bad" { console.writeLine("What's wrong?") } |
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"so so" { console.writeLine("It happens") } |
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: { console.writeLine("What happens?") }; |
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} |
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We could declare *while* loop which will be repeated until the condition is true: |
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public program() |
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{ |
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console.writeLine("Hello!").writeLine("Guess what?"); |
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var s := console.readLine(); |
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while (s != "nothing") |
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{ |
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console.writeLine("Guess what?"); |
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s := console.readLine(); |
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} |
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} |
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Alternatively *until* loop is executed until the condition is met : |
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public program() |
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{ |
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console.writeLine("Hello!").writeLine("Guess what?"); |
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var s := console.readLine(); |
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until (s == "nothing") |
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{ |
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console.writeLine("Guess what?"); |
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s := console.readLine(); |
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} |
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} |
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ELENA supports C-styled *for* loop as well: |
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public program() |
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{ |
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for(int n := 0, n < 5, n += 1) |
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{ |
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console.write("*") |
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} |
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} |
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The output is: |
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***** |
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_Note that comma is used instead of semicolon!_ |
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*doUntil* loop is similar to *for*, but the loop is executed at least once: |
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var text := new StringWriter(); |
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doUntil(string line, line.isEmpty(), line := console.readLine()) |
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{ |
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text.writeLine(line) |
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}; |
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== Classes, Fields Methods, Constructors == |
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Everything in ELENA is a class. So to implement some tasks we will have to declare our own classes. |
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=== Declaring a simple class === |
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Let's create a simple class : |
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import extensions; |
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class MyClass |
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{ |
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// a field |
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string myString; |
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// an implicit constructor |
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constructor(string s) |
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{ |
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myString := s |
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} |
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// an explicit constructor |
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constructor fromNuber(int n) |
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{ |
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myString := n.toString(); |
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} |
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// a method |
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printString() |
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{ |
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console.printLine(myString) |
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} |
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} |
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public program() |
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{ |
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// creating a class instance by sending new message to the class |
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var myClass := new MyClass("This is printed by my class."); |
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myClass.printString() |
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} |
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The output will be: |
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This is printed by my class. |
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*Note that in ELENA a class is an object itself and can be used by like any other object* |
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=== Class Inheritance === |
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We may inherit our class. When the parent is not explicitly declared - the class inherits *system'Object* super class |
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import extensions; |
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class MyParent |
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{ |
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constructor new() |
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{ |
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console.printLine("Parent Constructor.") |
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} |
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printMe() |
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{ |
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console.printLine("I'm a Parent Class.") |
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} |
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} |
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class MyChild : MyParent |
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{ |
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constructor new() |
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<= new() // calling the parent constructor |
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{ |
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console.printLine("Child Constructor.") |
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} |
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printMe() |
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{ |
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// calling the parent method |
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super.printMe(); |
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console.printLine("I'm a Child Class.") |
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} |
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} |
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public program() |
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{ |
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var myClass := MyChild.new(); |
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myClass.printMe() |
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} |
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The output is: |
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Parent Constructor. |
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Child Constructor. |
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I'm a Parent Class. |
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I'm a Child Class. |
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=== Private methods === |
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It is possible to declare the private methods which cannot be called outside the class. |
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import extensions; |
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class MyClass |
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{ |
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private printPrivate() |
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{ |
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console.printLine("private print.") |
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} |
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printPublic() |
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{ |
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console.print("Calling from public print - "); |
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// self is a reference to the current object |
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self.printPrivate() |
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} |
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} |
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public program() |
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{ |
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// Note that if the constructor explicitly is not declared |
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// the system'Object one (without input parameters) is inherited |
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var myClass := new MyClass(); |
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myClass.printPublic(); |
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myClass.printPrivate() |
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} |
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The output is: |
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Calling from public print - private print. |
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mytest'$private'MyClass : Method printPrivate[0] not found |
|||
Call stack: |
|||
system'Exception#class.new[1]:exceptions.l(125) |
|||
system'MethodNotFoundException#class.new[2]:exceptions.l(236) |
|||
system'$inline16.start[0]:win32_app.l(313) |
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mytest'program.#invoke[0]:test.l(26) |
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system'$inline16.start[0]:win32_app.l(39) |
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system'#startUp:win32_app.l(52) |
|||
=== Properties === |
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In normal case the class fields cannot be accessed outside the class. That's why we may declare special methods to access it: |
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import extensions; |
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class MyClass |
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{ |
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int _x; |
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get int x() = _x; // get accessor |
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set x(int o) // set accessor |
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{ |
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_x := o |
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} |
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} |
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public program() |
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{ |
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var myClass := new MyClass(); |
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myClass.x := 2; |
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console.printLine("MyClass.x=", myClass.x) |
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} |
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The output is: |
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MyClass.x=2 |
|||
We may simplify our code if we will use **prop** field template: |
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import extensions; |
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class MyClass |
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{ |
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int _x; |
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prop int x |
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{ |
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get() = _x; |
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set(int val) |
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{ |
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_x := val; |
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} |
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} |
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} |
|||
public program() |
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{ |
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var myClass := new MyClass(); |
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myClass.x := 2; |
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console.printLine("MyClass.x=", myClass.x) |
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} |
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Simple accessors can be omitted: |
|||
import extensions; |
|||
class MyClass |
|||
{ |
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prop int x; |
|||
} |
|||
public program() |
|||
{ |
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var myClass := new MyClass(); |
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myClass.x := 2; |
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console.printLine("MyClass.x=", myClass.x) |
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} |
|||
== Exception Handling == |
|||
We may use try-catch statement to handle the possible exceptions: |
|||
import extensions; |
|||
public program() |
|||
{ |
|||
try |
|||
{ |
|||
new Object().nonExistingMethod(); |
|||
} |
|||
catch(MethodNotFoundException e) |
|||
{ |
|||
console.printLine("Method not found") |
|||
} |
|||
catch(Exception e) |
|||
{ |
|||
console.printLine("Unknown error") |
|||
} |
|||
} |
|||
The output is : |
|||
Method not found |
|||
== See also == |
|||
* ELENA on [https://github.com/ELENA-LANG/elena-lang/ Github] |
|||
* ELENA on [https://www.reddit.com/r/elena_lang/ Reddit] |
* ELENA on [https://www.reddit.com/r/elena_lang/ Reddit] |
Latest revision as of 07:31, 4 September 2019
Elena
This programming language may be used to instruct a computer to perform a task.
Listed below are all of the tasks on Rosetta Code which have been solved using Elena.
This programming language may be used to instruct a computer to perform a task.
Official website |
---|
Execution method: | Compiled (bytecode) |
---|---|
Garbage collected: | Yes |
Type safety: | Safe |
Type strength: | Strong |
Type expression: | Implicit |
Type checking: | Dynamic |
See Also: |
ELENA is a general-purpose, object-oriented, polymorphic language with late binding. It features message dispatching/manipulation, dynamic object mutation, a script engine / interpreter and mix-ins.
Subcategories
This category has the following 3 subcategories, out of 3 total.
@
- Elena examples needing attention (empty)
- Elena Implementations (1 P)
- Elena User (2 P)
Pages in category "Elena"
The following 200 pages are in this category, out of 240 total.
(previous page) (next page)2
A
- A+B
- ABC problem
- Abstract type
- Abundant, deficient and perfect number classifications
- Accumulator factory
- Ackermann function
- Add a variable to a class instance at runtime
- AKS test for primes
- Amb
- Amicable pairs
- Anagrams
- Anonymous recursion
- Apply a callback to an array
- Arithmetic evaluation
- Arithmetic/Integer
- Array concatenation
- Array length
- Arrays
- Associative array/Creation
- Averages/Arithmetic mean
- Averages/Median
- Averages/Mode
- Averages/Root mean square
- Averages/Simple moving average
B
C
- Caesar cipher
- Calendar - for "REAL" programmers
- Call a function
- Call an object method
- Case-sensitivity of identifiers
- Catamorphism
- Character codes
- Check that file exists
- Classes
- Closures/Value capture
- Collections
- Combinations
- Command-line arguments
- Comments
- Compare a list of strings
- Compound data type
- Conway's Game of Life
- Copy a string
- Create a file
- Create a two-dimensional array at runtime
D
E
F
G
H
I
J
L
M
P
R
- Random number generator (included)
- Random numbers
- Read a file line by line
- Real constants and functions
- Reflection/List methods
- Reflection/List properties
- Remove duplicate elements
- Repeat a string
- Respond to an unknown method call
- Return multiple values
- Reverse a string
- Reverse words in a string
- Roman numerals/Decode
- Roman numerals/Encode
- Rot-13
- Run-length encoding
- Runtime evaluation
- Runtime evaluation/In an environment
S
- Search a list
- Search a list of records
- Send an unknown method call
- Sequence of primes by trial division
- Set of real numbers
- Short-circuit evaluation
- Simple windowed application
- Singleton
- Singly-linked list/Element definition
- Singly-linked list/Element insertion
- Singly-linked list/Traversal
- Sleep
- Sockets
- Sort an array of composite structures
- Sort an integer array
- Sort disjoint sublist
- Sort three variables
- Sort using a custom comparator
- Sorting algorithms/Bogosort
- Sorting algorithms/Bubble sort
- Sorting algorithms/Cocktail sort
- Sorting algorithms/Comb sort
- Sorting algorithms/Counting sort
- Sorting algorithms/Gnome sort
- Sorting algorithms/Insertion sort
- Sorting algorithms/Pancake sort
- Sorting algorithms/Quicksort
- Sorting algorithms/Selection sort
- Sorting algorithms/Sleep sort
- Sorting algorithms/Stooge sort
- Stack
- Stack traces
- String append
- String case
- String comparison
- String concatenation
- String interpolation (included)
- String length
- String matching
- String prepend
- Strip a set of characters from a string
- Strip whitespace from a string/Top and tail
- Substring
- Substring/Top and tail
- Sum and product of an array