Recursive functions

To define a function recursively, refer to it within the function body by the pseudo-identifier $$.

If the function is assigned to an identifier NAME using this syntax:

function NAME(FORMAL_IDFIER, ..., FORMAL_IDFIER)
    STATEMENTS
end function;

instead of:

NAME := function(FORMAL_IDFIER, ..., FORMAL_IDFIER)
    STATEMENTS
end function;

then the function may also be referred to by its own name within the function body.

The parser understands these two forms to be the same, except that any textual reference to NAME inside STATEMENTS is changed to the pseudo-identifier $$.

Example

> Fibonacci := func< n | n le 2 select 1 else $$(n-1) + $$(n-2) >;
> print Fibonacci(8);                                        
21

> function Lucas(n) 
function> if n eq 1 then       
function|if> return 1;                                   
function|if> elif n eq 2 then       
function|if> return 3;                                   
function|if> else            
function|if> return Lucas(n-1)+Lucas(n-2);               
function|if> end if;         
function> end function;   

OR

> Lucas := function(n) 
function> if n eq 1 then       
    ...
function|if> return $$(n-1)+$$(n-2);               
function|if> end if;         
function> end function;