Function

Function is used to encapsulate a series of calculations and algorithms.

There are two mode:

• function definition
• function call

Definition

Syntax:

@funcname (parameters) {
  ...//statements
}

funcname is the name of function, it has to follow the rule:

start with letter or underscore and the rest part can be number, letter or underscore.

parameters is a series of variables, like: name, age or anything you need.

e.g.

@plus(a, b)
{
  return a+b;
}

Here is a function named plus. It has two parameters named a and b. And its function is to calculate the sum of two parameters.

Call

Syntax:

funcname(arguments);

funcname is the name of defined function.

arguments is a series of values.

e.g.

plus(1, 2);

plus is the funcname, and 1, 2 correspond to parameter a and b.

Reference

Let’s see an example at first.

@foo(data)
{
  return data + 100;
}

a = 0;
a = foo(a);

This program just modified a from 0 to 100, and that is what we wish it to be.

But the last statement is a little bit clumsy. How to make it better?

@foo(&data)
{
  data += 100;
}

a = 0;
foo(a);

We change function parameter data to be &data.

Operator & makes argument a to be a reference variable named data in function foo. Every modification on data will directly effect on a.

Note:

1. & only can be used on the parameters of function definition.
2. array and object will be treated as reference all the time no matter & given or not.

Lack of arguments

@foo(data)
{
  Dump(data);
}

foo();

This program will not report error. Because interperter will set nil to data automatically.

Return function

Let’s see an example:

@foo() {
  @bar() {
    sys = Import('sys');
    sys.print('bar');
  }
  return bar;
}

@foo()();

Guess what happened?

‘bar’ will be printed on terminal.

It is possible because function definition is a statement. So we can define a function in another function’s definition.

Variable arguments

In most programming languages, they all support variable arguments. In melang, we have an alternative plan.

@log()
{
  sys = Import('sys');

  s = 'argument list: ';
  for (i = 0; i < sys.size(args); ++i) {
      s += args[i] + ' ';
  }
  sys.print(s);
}

log('this', 'is', 'a', 'variable', 'arguments', 'example');

The result of this program is:

argument list: this is a variable arguments example 

The key point is variable args. It’s a internal variable in Melang function.

It is an array to record every arguments passed to this function.

Function sys.size returns the number of array elements.

Closure

Let us see an example at first.

@foo()
{
  a = 1;
  @bar()
  {
    sys = Import('sys');

    sys.print(a);
  }
  return bar;
}

b = foo();
b();

In this example, I want to output the value of a which is defined in function foo in function bar. Obviously, the output is nil, because a can not be found in function bar.

But there is a way to get a in bar.

@foo()
{
  a = 1;
  @bar() $(a)
  {
    sys = Import('sys');
    sys.print(a);
  }
  return bar;
}

b = foo();
b();

Now, the output is 1.

Let us modify this example again:

@foo()
{
  a = 1;
  @bar() $(a)
  {
    sys = Import('sys');
    sys.print(a);
  }
  a = 100; //change to another value
  return bar;
}

b = foo();
b();

Now, the output still be 1. How can I do if I want the value a in function bar is the modified value (100)?

@foo()
{
  a = 1;
  @bar() $(&a) //to become a reference
  {
    sys = Import('sys');
    sys.print(a);
  }
  a = 100; //change to another value
  return bar;
}

b = foo();
b();