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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 program symbol 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 simplest (generic, i.e. without an explicit signature) message consists of an action and a parameter list. |
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The statement should be terminated by a dot (ELENA is inspired by Smalltalk and uses its syntax notations). |
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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 literal 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 separated by a semicolon: |
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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 literal 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 normal case 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 still possible to specify the variable expected type: |
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T<LiteralValue> s := "Hello". |
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console writeLine(s). |
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where system'LiteralValue 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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literal s := "Hello". // literal is a LiteralValue alias |
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console writeLine(s). |
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Note that despite it we may still assign the objects of different types without a compile-time error: |
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literal s := "Hello". |
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s := T<literal>(2). |
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Why? ELENA is a dynamic language and in most cases resolves the types in run-time. So our code will be actually |
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compiled as follow: |
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literal s := "Hello". |
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s := T<literal>(2) |
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It is guaranteed that the result of the cast message is an instance of LiteralValue, so if the object supports the message the conversion will be done quietly. |
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The output will be: |
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system'RealNumber : Method $system'IntNumber not found |
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Call stack: |
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system'Exception#class.new$system'LiteralValue[1]:exceptions.l(125) |
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system'MethodNotFoundException#class.new$system'Object$system'Message[2]:exceptions.l(213) |
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system'#inline1BF.start[1]:win32_app.l(252) |
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mytest'program.#invoke[0]:test.l(5) |
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system'BaseFunction.eval[0]:control.l(172) |
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system'#inline1BF.start[1]:win32_app.l(37) |
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system'startUp(5) |
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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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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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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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LiteralValue is used to store the text encoded in UTF-8. LiteralValus is 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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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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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$system'LiteralValue[1]:exceptions.l(125) |
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system'OutOfRangeException#class.new[0]:exceptions.l(149) |
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system'LiteralValue.getAt$system'IntNumber[1]:memory.l(1191) |
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mytest'program.#invoke[0]:test.l(8) |
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system'BaseFunction.eval[0]:control.l(172) |
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system'#inline1BF.start[1]:win32_app.l(37) |
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system'startUp(5) |
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We may use another class representing UTF-16 text (WideLiteralValue) to solve this problem: |
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import extensions. |
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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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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 enumerator; firstMember). |
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console printLine("The last character of ",s," is ", s enumerator; 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 type === |
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It is possible to declare a dynamic or static array. |
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import extensions. |
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program = |
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[ |
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var staticArray := (1,2,3). |
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var dynamicArray := Array new(3). |
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dynamicArray[0] := 1. |
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dynamicArray[1] := "b". |
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dynamicArray[2] := 2.3r. |
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console printLine("static array ",staticArray). |
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console printLine("dynamic array ",dynamicArray). |
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]. |
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The output is: |
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static array 1,2,3 |
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dynamic 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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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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== 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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[ /* doSomething if TRUE*/ ]; |
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[ /*doSomehting if ELSE*/ ]. |
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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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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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[ console writeLine("Me too") ]; |
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[ console writeLine("What happends?") ] |
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]. |
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Several conditions can be checked: |
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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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[ console writeLine("Me too") ]; |
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[ console writeLine("What happens?") ] |
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]. |
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A switch statement can be implemented using => operator: |
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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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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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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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== 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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literal myString. |
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// a constructor |
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constructor new(literal s) |
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[ |
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myString := s. |
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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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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 := MyClass new("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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print |
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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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print |
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[ |
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// calling the parent method |
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$super print. |
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console printLine("I'm a Child Class.") |
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] |
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} |
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program = |
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[ |
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var myClass := MyChild new. |
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myClass print. |
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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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// $self is a reference to the current object |
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self printPrivate. |
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] |
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} |
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program = |
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[ |
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// Note that if the constructor explicitly is not declared |
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// the system'Object one (without input parameters) is inherited |
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var myClass := MyClass new. |
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myClass printPublic. |
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myClass printPrivate. |
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]. |
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The output is: |
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Calling from public print - private print. |
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mytest'MyClass : Method mytest#printPrivate not found |
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Call stack: |
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system'Exception#class.new$system'LiteralValue[1]:exceptions.l(125) |
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system'MethodNotFoundException#class.new$system'Object$system'Message[2]:exceptions.l(213) |
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system'#inline1BF.start[1]:win32_app.l(252) |
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mytest'program.#invoke[0]:test.l(24) |
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system'BaseFunction.eval[0]:control.l(172) |
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system'#inline1BF.start[1]:win32_app.l(37) |
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system'startUp(5) |
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=== Properties === |
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In normal case the class fields cannot be accessed outside the class. That's why we may declare a special method 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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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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program = |
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[ |
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var myClass := MyClass new. |
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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 |
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We may simplify our code if we will use prop attribute: |
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import extensions. |
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class MyClass |
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{ |
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int prop x :: _x. |
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} |
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program = |
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[ |
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var myClass := MyClass new. |
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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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== Exception Handling == |
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We may use try-catch statement to handle the possible exceptions: |
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import extensions. |
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import system'io. |
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program = |
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[ |
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try(console printLine(File new("notexistingfile.txt"); content)) |
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{ |
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on(Exception ex) |
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[ |
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console printLine("Unknown error - ",ex). |
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] |
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on(IOException ex) |
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[ |
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console printLine("I/O error - ",ex). |
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] |
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} |
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]. |
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The output is : |
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I/O error - Cannot open the file |
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Call stack: |
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system'Exception#class.new$system'LiteralValue[1]:exceptions.l(125) |
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system'io'IOException#class.new$system'LiteralValue[1]:io\ioexceptions.l(10)system'io'FileStream#class.new$system'WideLiteralValue$system'IntNumber$system'IntNumber$system'IntNumber$system'IntNmber[5]:io\win32_files.l(52) |
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system'io'FileStream#class.openForRead[1]:io\win32_files.l(29) |
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system'io'StreamReader#class.new[1]:io\win32_files.l(207) |
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system'io'fileControl.reader[1]:io\win32_files.l(269) |
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system'io'File.read$system'text'TextBuilder[1]:io\files.l(59) |
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system'io'File.content[0]:io\files.l(33) |
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mytest'program.#invoke[0]:test.l(6) |
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system'BaseFunction.eval[0]:control.l(172) |
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system'#inline1BF.start[1]:win32_app.l(37) |
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system'startUp(5) |
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== 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 |
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Execution method: | Compiled (bytecode) |
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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 241 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
- Associative array/Iteration
- 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