Category: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.
The simplest program
To create a simple console program we have to declare the public **program** closure in the project root namespace:
public program() { }
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*.
The statement should be terminated by a semicolon.
public program() { console.writeLine("Hello!"); }
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).
Several message operations can be done in a single statement:
public program() { console.writeLine("Hello!").writeLine("How are you?"); }
The result will be:
Hello! How are you?
We may read a user input by sending **readLine** message without parameters:
public program() { console.write("What is your name:").writeLine("Hello " + console.readLine()) }
The result will be:
What is your name:Alex Hello Alex
- Console::write** method is similar to **writeLine** except that it writes to the output screen without a new line character.
Declaring a variable
A variable can be declared in an assignment statement starting with **var** attribute:
var myVariable := "A text";
where we declare a variable **myVariable** and initialize it with a string constant value.
The assigning value can be an expression itself:
public program() { console.writeLine("Hello!").writeLine("How are you?"); var s := console.readLine() }
ELENA is a dynamic language and in most cases we may not specify the variable type:
public program() { var s := "Hello"; console.writeLine(s);
s := 2; console.writeLine(s); }
The output will be:
Hello 2
But it is possible to specify the variable expected type:
String s := "Hello"; console.writeLine(s);
- where system'String is a class representing text as a sequence of UTF-8 characters.*
We may use a class alias to simplify the code:
string s := "Hello"; // string is a String class alias console.writeLine(s);
ELENA does not enforce types in compilation-time, so the following code will be successfully compiled:
string s := "Hello"; s := 2;
But it will raise an exception in the run-time:
system'IntNumber : Method #cast[0] not found Call stack: system'Exception#class.new[1]:exceptions.l(125) system'MethodNotFoundException#class.new[2]:exceptions.l(236) system'$inlineC.start[0]:win32_app.l(313) mytest'program.#invoke[0]:test.l(5) system'$inlineC.start[0]:win32_app.l(39) system'#startUp:win32_app.l(52)
As you may see, the compiler injects the typecasting code, so the actual code looks like this:
string s := "Hello"; s := cast string(2);
- where* **cast string(2)** *is a construction to typecast the target expression* - **a numeric constant** - *to the expected type* - **System'String**
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:
public program() { real r := 2; console.writeLine(r) }
will be successfully executed with the result:
2.0
Basic Types
The Boolean Type
Boolean type is used in conditional operations and may accept only two Boolean literals - **true** and **false**.
import extensions; public program() { bool b1 := true; bool b2 := false; console.printLine(b1,"==",b1," is ",b1==b1); console.printLine(b2,"==",b2," is ",b2==b2); console.printLine(b1,"==",b2," is ",b1==b2); console.printLine(b2,"==",b1," is ",b1==b2); }
- Note that implicit extension method - **extensions'outputOp.printLine[]** - was used to simplify the output operations.*
The output is:
true==true is true false==false is true true==false is false false==true is false
The Numeric types
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**):
import extensions; public program() { int n := -234; long l := 1235456765l; real r := 2.3456r; console.printLine("Integer number - ",n); console.printLine("Long integer number - ",l); console.printLine("Real number - ",r) }
The output is:
Integer number - -234 Long integer number - 1235456765 Real number - 2.3456
The String Type
- 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!*.
import extensions; public program() { var s := "Hello"; console.printLine("The first character of ",s," is ", s[0]); console.printLine("The last character of ",s," is ", s[s.Length - 1]) }
The output is:
The first character of Hello is H The last character of Hello is o
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.
import extensions;
public program() { var s := "Привет"; console.printLine("The first character of ",s," is ", s[0]); console.printLine("The last character of ",s," is ", s[s.Length - 1]) }
The output is:
The first character of Привет is П An index is out of range Call stack: system'Exception#class.new[1]:exceptions.l(125) system'OutOfRangeException#class.new[1]:exceptions.l(156) system'OutOfRangeException#class.new[0]:exceptions.l(156) system'String.at[1]:memory.l(1243) mytest'program.#invoke[0]:test.l(8) system'$inlineC.start[0]:win32_app.l(39) system'#startUp:win32_app.l(52)
We may use another class representing UTF-16 text (**WideString**) to solve this problem:
import extensions; public program() { var s := "Привет"w. // UTF-16 string console.printLine("The first character of ",s," is ", s[0]); console.printLine("The last character of ",s," is ", s[s.Length - 1]); }
The output will be correct this time:
The first character of Привет is П The last character of Привет is т
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:
import system'routines; import extensions; public program() { var s := "Привет"; console.printLine("The first character of ",s," is ", s.FirstMember); console.printLine("The last character of ",s," is ", s.LastMember) }
The output will be correct for any UTF-8 text:
The first character of Привет is П The last character of Привет is т
Array types
It is possible to declare a generic (_system'Array_) or strong-typed template-based (_system'Array#1_) array.
import extensions; public program() { var strongTypedArray := new int[] {1,2,3}; var genericArray := Array.allocate(3); genericArray[0] := 1; genericArray[1] := "b"; genericArray[2] := 2.3r; console.printLine("strong-typed array ",strongTypedArray.asEnumerable()); console.printLine("dynamic-typed array ",genericArray.asEnumerable()); }
The output is:
strong-typed array 1,2,3 dynamic-typed array 1,b,2.3
Basic arithmetic operations
ELENA supports basic arithmetic operations with integer and floating-point numbers:
import extensions; public program() { var n1 := 12; var n2 := 5; var n3 := -3; var r1 := 2.3r; console.printLine(n1, " + ", n2, " = ", n1 + n2); console.printLine(n1, " - ", n2, " = ", n1 - n2); console.printLine(n1, " * ", n3, " = ", n1 * n3); console.printLine(n1, " / ", n2, " = ", n1 / n2);
console.printLine(n1, " + ", n2, " * ", r1 ," = ", n1 + n2 * r1) }
The result is:
12 + 5 = 17 12 - 5 = 7 12 * -3 = -36 12 / 5 = 2 12 + 5 * 2.3 = 23.5
?? operator
Operator ?? is used to deal with nil.
_a ?? b_ - will return _a_ if _a_ is not _nil_ or _b_
See the following code:
import extensions; public program() { var a := nil; var b := a ?? 0 + 2; console.printLine(a ?? "nil", " ?? 0 + 2 = ", b); a := 1; b := a ?? 0 + 2; console.printLine(a ?? "nil", " ?? 0 + 2 = ", b); }
The output is:
nil ?? 0 + 2 = 2 1 ?? 0 + 2 = 3
The operator can be used for typecasting operations as well:
_cast type(a) ?? b_ - will typecast _a_ to _type_ or return _b_ if it is not possible.
See the code:
import extensions; public program() { string s := "a"; var n := 2; console.printLine("cast int(",s,") ?? 0 = ", cast int(s) ?? 0); console.printLine("cast int(",n,") ?? 0 = ", cast int(n) ?? 0); }
The output is:
cast int(a) ?? 0 = 0 cast int(2) ?? 0 = 2
Conditions, Multi-select, Loops
Conditional statement in ELENA are defined as follows:
if(<Boolean expression>) { /* doSomething if TRUE*/ } else { /*doSomehting if ELSE*/ };
We could omit else part
if(<Boolean expression>) { /*doSomehting if TRUE*/ };
Usually Boolean expression is a result of a comparison operation:
public program() { console.writeLine("Hello!").writeLine("How are you?"); var s := console.readLine(); if(s == "good") { console.writeLine("Me too") } else { console.writeLine("What happends?") } }
Several conditions can be checked:
public program() { console.writeLine("Hello!").writeLine("How are you?"); var s := console.readLine(); if((s == "good") || (s == "fine")) { console.writeLine("Me too") } else { console.writeLine("What happends?") } }
A switch statement can be implemented using => operator:
public program() { console.writeLine("Hello!").writeLine("How are you?"); var s := console.readLine(); s => "good" { console.writeLine("Me too") } "fine" { console.writeLine("Glad to hear") } "bad" { console.writeLine("What's wrong?") } "so so" { console.writeLine("It happens") } : { console.writeLine("What happens?") }; }
We could declare *while* loop which will be repeated until the condition is true:
public program() { console.writeLine("Hello!").writeLine("Guess what?"); var s := console.readLine(); while (s != "nothing") { console.writeLine("Guess what?"); s := console.readLine(); } }
Alternatively *until* loop is executed until the condition is met :
public program() { console.writeLine("Hello!").writeLine("Guess what?"); var s := console.readLine(); until (s == "nothing") { console.writeLine("Guess what?"); s := console.readLine(); } }
ELENA supports C-styled *for* loop as well:
public program() { for(int n := 0, n < 5, n += 1) { console.write("*") } }
The output is:
*****
_Note that comma is used instead of semicolon!_
- doUntil* loop is similar to *for*, but the loop is executed at least once:
var text := new StringWriter(); doUntil(string line, line.isEmpty(), line := console.readLine()) { text.writeLine(line) };
Classes, Fields Methods, Constructors
Everything in ELENA is a class. So to implement some tasks we will have to declare our own classes.
Declaring a simple class
Let's create a simple class :
import extensions; class MyClass { // a field string myString; // an implicit constructor constructor(string s) { myString := s } // an explicit constructor constructor fromNuber(int n) { myString := n.toString(); } // a method printString() { console.printLine(myString) } } public program() { // creating a class instance by sending new message to the class var myClass := new MyClass("This is printed by my class."); myClass.printString() }
The output will be:
This is printed by my class.
- Note that in ELENA a class is an object itself and can be used by like any other object*
Class Inheritance
We may inherit our class. When the parent is not explicitly declared - the class inherits *system'Object* super class
import extensions; class MyParent { constructor new() { console.printLine("Parent Constructor.") } printMe() { console.printLine("I'm a Parent Class.") } } class MyChild : MyParent { constructor new() <= new() // calling the parent constructor { console.printLine("Child Constructor.") } printMe() { // calling the parent method super.printMe(); console.printLine("I'm a Child Class.") } } public program() { var myClass := MyChild.new(); myClass.printMe() }
The output is:
Parent Constructor. Child Constructor. I'm a Parent Class. I'm a Child Class.
Private methods
It is possible to declare the private methods which cannot be called outside the class.
import extensions; class MyClass { private printPrivate() { console.printLine("private print.") } printPublic() { console.print("Calling from public print - "); // self is a reference to the current object self.printPrivate() } } public program() { // Note that if the constructor explicitly is not declared // the system'Object one (without input parameters) is inherited var myClass := new MyClass(); myClass.printPublic(); myClass.printPrivate() } The output is:
Calling from public print - private print. 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'$inline16.start[0]:win32_app.l(313) mytest'program.#invoke[0]:test.l(26) system'$inline16.start[0]:win32_app.l(39) system'#startUp:win32_app.l(52)
Properties
In normal case the class fields cannot be accessed outside the class. That's why we may declare special methods to access it:
import extensions;
class MyClass { int _x; get int x() = _x; // get accessor set x(int o) // set accessor { _x := o } } public program() { var myClass := new MyClass(); myClass.x := 2; console.printLine("MyClass.x=", myClass.x) }
The output is:
MyClass.x=2
We may simplify our code if we will use **prop** field template:
import extensions; class MyClass { int _x; prop int x { get() = _x; set(int val) { _x := val; } } } public program() { var myClass := new MyClass(); myClass.x := 2; console.printLine("MyClass.x=", myClass.x) }
Simple accessors can be omitted:
import extensions; class MyClass { prop int x; } public program() { var myClass := new MyClass(); myClass.x := 2; console.printLine("MyClass.x=", myClass.x) }
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
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.
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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