A parameterless function used as an expression is not called

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This bug report demonstrates a problem with parameterless functions.

The following piece of code

#lang algol60
begin
  integer procedure getvalue;
     getvalue := 4;

  integer i;
  i := getvalue;
  printnln(i)
end

fails with this message: bad value: expected a number, got #<procedure:getvalue> In my understanding, the problem is that in

i := getvalue;

the function getvalue is not called. Instead, the generated code attempts to assign a function to an integer, which of course fails. The following modified example works:

#lang algol60
begin
  integer procedure getvalue(arg);
     Boolean arg;
     getvalue := 4;
  integer i;
  i := getvalue(true);
  printnln(i)
end

This works because the call of a function with parameters is unambiguous.

To further clarify the more tricky aspects of parameterless functions, consider the following example:

#lang algol60

begin
  real procedure r;
  begin
    r := 5.0;
  end;

  real procedure p1(rv, rp);
    real rv;
    real procedure rp;
  begin
    p1 := rv + rp
  end;
  printnln(p1(r, r))
end

In Racket Algol 60 this does not work. Note that in the expression p1(r, r) the first occurance of r is a function call, while the second isn't. For some reason, Racket Algol 60 does not see the difference because r is parameterless.

Again, the introduction of a dummy parameter (to function r) disambiguates a function call from a reference to a function:

#lang algol60
begin
  real procedure r(x);
    Boolean x;
  begin
    r := 5.0;
  end;

  real procedure p1(rv, rp);
    real rv;
    real procedure rp;
  begin
    p1 := rv + rp(true)
  end;

  printnln(p1(r(true), r))
end

Now a function call requires a syntax that is different from a function reference and everything is fine.