Citrine (programming language): Difference between revisions

Revision as of 18:10, 16 May 2020

Revision as of 21:14, 21 May 2020

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A Citrine program is basically a sequence of messages sent to objects. For instance, to determine whether 5 is an even number, the message 'even?' is sent to the number 5.

<sourcesyntaxhighlight lang="smalltalk">

5 even?

</syntaxhighlight>

</source>

This is called a ''unary'' message because it takes no arguments. A ''binary'' message is always a single UTF-8 character; this differs from Smalltalk, where there is a fixed set of binary messages. Here is an example:

<sourcesyntaxhighlight lang="smalltalk">

6 + 7.

</syntaxhighlight>

</source>

Here a binary message '+' is sent to number 6, the argument of this binary message is '7', this will result in a new number object '13'. Assigning the outcome of this operation to a variable uses the assignment operator: :=.

<sourcesyntaxhighlight lang="smalltalk">

total := money + debt.

</syntaxhighlight>

</source>

Also note that each line in a Citrine program ends with a dot, just like in Smalltalk. Besides unary and binary messages, Citrine offers ''keyword messages'', which take arguments interspersed with the message itself just like Smalltalk and [[Objective-C]].

<sourcesyntaxhighlight lang="smalltalk">

☞ x := Number between: 1 and: 5.

</syntaxhighlight>

</source>

The code snippet above will return a boolean object ''True''.

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Just like Smalltalk, control flow in Citrine is implemented by strategic use of messages. For instance, writing a conditional statement requires sending a block of code to a boolean.

<sourcesyntaxhighlight lang="smalltalk">

(money > price) true: { ✎ write: 'Yes, you can afford this'. }.

</syntaxhighlight>

</source>

Likewise, a for-loop is written as:

<sourcesyntaxhighlight lang="smalltalk">

{ :step ✎ write: 'this is step:' + step. } * 10.

</syntaxhighlight>

</source>

To break out of a loop in Citrine one has to send the message 'break' to a boolean, this allows a conditional break from a loop without having to factor out the break conditions:

<sourcesyntaxhighlight lang="smalltalk">

{ :i

(i = 3) break.

✎ write: i.

} * 5.

</syntaxhighlight>

</source>

==Pipelines==

Unlike Smalltalk, Citrine has no semi-colon to send a message to the original receiver. Instead Citrine has a comma token ',' used to chain keyword messages, this allows writing Unix-like ''[[Pipeline (Unix)|pipelines]]''. The following code uses a pipeline-like syntax to replace all the 'o' characters with zeroes, the resulting string would be something like: '1010101...'.

<sourcesyntaxhighlight lang="smalltalk">

onesAndZeroes := '1o1o1o1o1o1' split: 'o', map: mapUp, join: '0'.

</syntaxhighlight>

</source>

==Prototypes==

The biggest difference from Smalltalk is the use of prototypes. Citrine does not have a concept of a class, it only knows about objects. An object is created using the new message:

<sourcesyntaxhighlight lang="smalltalk">

cat := Object new.

</syntaxhighlight>

</source>

This object can be made to respond to messages by ordering the object to listen to events. This is kind of similar to

adding methods in languages like [[Java (programming language)|Java]]:

<sourcesyntaxhighlight lang="smalltalk">

cat on: 'meow' do: {

Pen write: 'meow!'.

}.

</syntaxhighlight>

</source>

As stated above, inheritance is based on prototypes. To derive an object from another object, the new message must be sent to the object to be extended:

<sourcesyntaxhighlight lang="smalltalk">

☞ Animal := Object new.

Animal on: 'makeSound' do: {

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☞ Tom := Cat new.

Tom makeSound.

</syntaxhighlight>

</source>

==Unicode==

Citrine uses UTF-8 unicode extensively, both objects and messages can consist of unicode symbols. All string length are calculated using UTF-8. Citrine distinguishes string length and size in bytes:

<sourcesyntaxhighlight lang="smalltalk">

'text' length.

</syntaxhighlight>

</source>

returns the length of the string in UTF-8 code pointes, while:

<sourcesyntaxhighlight lang="smalltalk">

'text' bytes.

</syntaxhighlight>

</source>

returns the number of bytes.

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The following demonstration makes the Mailer object available in the module:

<sourcesyntaxhighlight lang="smalltalk">

Application := {

☞ mailer := Mailer new.

module run.

}.

</syntaxhighlight>

</source>

==See also==