Category:Elena: Difference between revisions

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Several parameters can be passed in the message as well:

control foreach: (1,2,3) &do:printingLn.

control foreach: (1,2,3) do:printingLn.

Ampersand is used to indicate that the signature has several arguments (subjects). The actual message name is eval&foreach&do(2).

The generic message can have several parameters as well:

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class DerivedClass :: BaseClass

{

constructor new &field1:aField2 &field2:aField2

constructor new field1:aField2 field2:aField2

[

theField1 := aField1.

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]

add &field1:aField2 &field2:aField2

add field1:aField2 field2:aField2

= MyClass new &Field1:(theField1 + aField1) &Field2:(theField2 + aField2).

= MyClass new Field1:(theField1 + aField1) Field2:(theField2 + aField2).

}

To create a class instance we have to send a message (usually new) to its symbol (a class symbol is declared implicitly for every class and can be used as a normal one)

var anObject := DerivedClass new &field1:1 &field2:1. // DerivedClass is a symbol

var anObject := DerivedClass new field1:1 field2:1. // DerivedClass is a symbol

Singletons cannot have constructors and their symbols can be used directly

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{

sumOf:a:b

= a add &field1:b &field2:a.

= a add field1:b field2:a.

}

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In general the symbol is a named expression and can be used to declare initialized objects, constants, reusable expressions and so on.

symbol ZeroClass = DerivedClass new &field:0 &field:0.

symbol ZeroClass = DerivedClass new field:0 field:0.

A static symbol is the class instance which state is preserved. There could be only one instance of static symbol.

static SingletonClass = DerivedClass new &field:0 &field:0.

static SingletonClass = DerivedClass new field:0 field:0.

== Code blocks ==

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ELENA code block consists of a sequence of statements. The block is enclosed in square brackets and may contain nested sub code blocks (which in fact are inline action classes). The statement terminator is a dot.

printAckermann &n:n &m:m

printAckermann n:n m:m

[

control forrange &int:0 &int:n &do: (&int:i)

control forrange int:0 int:n do: (&int:i)

[

control forrange &int:0 &int:m &do: (&int:j)

control forrange int:0 int:m do: (&int:j)

[

...

console writeLine.

console writeLine

].

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...

^ aRetVal / anArray length.

^ aRetVal / anArray length

]

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Number = convertor toReal:theValue.

or there is an alternative block expression

[ convertor toReal:theValue ]

Note: it should not end with the terminator symbol

It is possible to declare the block variable and assigns the value to it. The variable name must be unique within the code block scope.

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(m == 0)

? [ n + 1 ]

? [ ^n + 1 ]

! [ m + n ].

! [ ^m + n ].

Note: the main difference between using explicit messages and conditional operators is that the compiler may optimize the resulting code in the later case.

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(m == 0)

! [ m / n ].

! [ ^m / n ].

It is possible to use *if* template code :

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if (aChar >= 48) and:(aChar < 58)

[

theToken += aChar.

theToken append:aChar.

];

[

Exception new:"Invalid expression" raise.

Exception new:"Invalid expression"; raise.

]

Note that in this case both condition will be evaluated even if the first one is false If we want to use short-circuit evaluation expression brackets should be used

if ((x >= 0)and:[ array@x != 0])

if ((x >= 0)and:$(array@x != 0))

[

...

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A switch statement can be implemented using => operator

^ aBulls =>

aBulls =>

-1 [ consoleEx writeLine:"Not a valid guess.". ^ true. ];

-1 [ consoleEx writeLine:"Not a valid guess.". ^ true ];

4 [

consoleEx writeLine:"Congratulations! You have won!".

^ false.

^ false

];

! [

theAttempt += 1.

theAttempt append:1.

consoleEx writeLine:

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: " bulls and " : aCows : " cows".

^ true.

^ true

].