Re: [Seed7-users] Functions & Procedures Confusion

[Thomas M. <tho...@gm...>]

There are two things that use the keyword 'func'.

1. There are types like 'func integer' or 'func boolean'.
2. There is the 'func ... begin ... end func' construct.

The type 'proc' is defined as 'func void'. The type 'void'
describes that there is no value. In fact 'void' has a value,
but there is just one value: 'empty'. So the type 'func void'
aka 'proc' means: A function that returns nothing. In Pascal
and other languages this is called procedure. In Seed7 the
name function refers also to procedures as they are functions
that return 'void'.

The 'func ... begin ... end func' construct comes in several
variants.

An example of a procedure declarations is:

  const proc: main is func
    begin
      writeln("hello world");
    end func;

The 'func ... begin ... end func' construct is used to initialize
the 'main' procedure.

A variant of this func construct is used to define a procedure
with local variables. E.g.:

  const proc: main is func
    local
      var integer: number is 0;
    begin
      for number range 10 downto 0 do
        writeln(number);
      end for;
    end func;

Functions (that do not return void) are initialized with
another variant of the construct:
'func result ... begin ... end func'.

  const func string: foo is func
    result
      var string: stri is "";
    begin
      for 3 do
        stri &:= rand('a', 'z');
      end for;
    end func;

A function with a local variable is:

  const func string: bar is func
    result
      var string: stri is "";
    local
      var integer: number is 0;
    begin
      for number range 1 to rand(1, 10) do
        stri &:= str(number);
      end for;
    end func;

So 'func begin ...' and 'func local ...' are used to
define procedures (aka proc).

And 'func result ...' is used to define functions (except
func void aka proc).

As you figured out the 'func ...' construct is overloaded.

There is another way to define a function. This way is
used when an expression can describe the function body:

  const func integer: random10 is
    return rand(1, 10);

I hope this helps.

Regards Thomas