F/fn

F/fn keyword

F <name>(<arguments>) [-> <return_type>]
   <body>

<name>

Name of the function. Can be empty if it is a constructor (when function defined inside type definition, example: {…

T Person
   String name
   Int age

   F (name, age)
      .name = name
      .age  = age

}) or this is a module-default-function, e.g.

os:(command_string)

(see module os documentation).

<arguments>

Comma-separated list of function's arguments. Can be empty.
Each argument is defined as:
[<argument type>] [<qualifier>]<argument name> [= <default value>]

By default all arguments passed to a function are constant and can not be changed inside a function, but this behaviour can be altered via qualifiers.
Qualifiers

Make a local copy of argument. Make it possible to change an argument inside a function. In this case only local copy of argument will be changed.

Pass an argument by reference. Make it possible to change an argument inside a function.

Example:

F f(=i, j)
   i += 1 // this is correct
   j += 1 // but here is an error

Named arguments

F sqlen(x = 0, y = 0, z = 0)
   R x*x + y*y + z*z

print(sqlen(z' 3)) // equivalent to print(sqlen(0, 0, 3))

Named-only [or keyword-only] arguments

F to_html(instr, ohd = 0B, ', habr_html = 0B)
   ...

to_html(s, 0B, 1B) // this is wrong
to_html(s, 0B, habr_html' 1B) // this is correct
to_html(s, habr_html' 1B) // and this is correct

F/fn subkeywords

F.destructor

fn.destructor

is used to define a destructor:

T TypeName
   F.destructor
      print(‘TypeName destructor called’)

Subkeywords

virtual.new

virtual.override

virtual.final

and

virtual.abstract

indicate that this functions is virtual and they specify a "virtual type" of this function.

virtual.new

means that this is a new virtual function.

virtual.override

ensures that the function is virtual and is overriding a virtual function from a base type. The program is ill-formed (a compile-time error is generated) if this is not true.

virtual.final

specifies that a virtual function cannot be overridden in a derived type.

virtual.abstract

subkeyword enables you to create type functions that are incomplete and must be implemented in a derived type.
Small example:

T Shape
   F.virtual.abstract square() -> Float

T Circle(Shape, Object)
   Float radious
   F.virtual.override square() -> Float
      R pi * radious^2

F.args

fn.args

is intended to provide access to the arguments passed to the current function, but it is not implemented yet.