Editing Io (programming language) (section)

== Syntax ==
{{Unreferenced section|date=June 2013}}
In its simplest form, Io [[Syntax (programming languages)|syntax]] is composed of one identifier:<ref>{{Cite web |title=io guide |url=https://iolanguage.org/guide/guide.html#Syntax |access-date=2023-06-22 |website=iolanguage.org}}</ref>

<syntaxhighlight lang="io">
 doStuff
</syntaxhighlight>

Assuming the above doStuff is a [[Method (computer programming)|method]], it is being called with zero arguments and as a result, explicit parentheses are not required.

If doStuff had arguments, it would look like this:

<syntaxhighlight lang="io">
 doStuff(42)
</syntaxhighlight>

Io is a [[message passing]] language, and since everything in Io is a message (excluding [[Comment (computer programming)|comment]]s), each message is sent to a receiver. The above example demonstrates this well, but not fully. To describe this point better, let's look at the next example:

<syntaxhighlight lang="io">
 System version
</syntaxhighlight>

The above example demonstrates message passing in Io; the "version" message is sent to the "System" object.

[[Operator (computer programming)|Operators]] are a special case where the syntax is not as cut-and-dried as the above examples. The Io [[Syntax analysis|parser]] intercepts a set of operators defined by the interpreter, and translates them to method calls. For example, the following:

<syntaxhighlight lang="io">
 1 + 5 * 8 + 1
</syntaxhighlight>

translates to:

<syntaxhighlight lang="io">
 1 +(5 *(8)) +(1)
</syntaxhighlight>

All operators in Io are methods; the fact that they do not require explicit parentheses is a convenience. As you can see, there is also a little bit of [[operator precedence]] happening here, and the precedence levels are the same as with the [[Operator precedence in C|C precedence levels]].

=== Methods and blocks ===
In Io there are two ways of creating [[anonymous function]]s: methods and blocks. Between them, they are almost identical except for [[Scope (programming)|scope]]. While blocks have [[lexical scope]], methods have [[dynamic scope]].

Both ''method'' and ''block'' are [[higher-order function]]s.

=== Examples ===
The ubiquitous [[Hello world program]]:

<syntaxhighlight lang="io">
 "Hello, world!" println
</syntaxhighlight>

New objects are created by [[Cloning (programming)|cloning]] objects. In Io specifically, a new, empty object is created and only the differences between it and its parent are stored within the new object; this behavior is known as [[differential inheritance]]. An example of this behavior is shown:

<syntaxhighlight lang="io">
 A := Object clone         // creates a new, empty object named "A"
</syntaxhighlight>

A simple non-recursive factorial function, in Io:

<syntaxhighlight lang="io">
factorial := method(n,
    if(n == 0, return 1)
    res := 1
    Range 1 to(n) foreach(i, res = res * i)
)
</syntaxhighlight>

Because assignment of <code>res * i</code> to <code>res</code> is the last action taken, the function implicitly returns the result and so an explicit return expression is not needed. The above demonstrates the usage of [[Range (computer programming)|ranges]], and doesn't use a <code>for()</code> loop, which would be faster.