% To declare things you can either write an .spc file or you can use
% the clu file itself as a specfile.  For a small program a common
% idiom is to spec and compile the same source file:
%
%   pclu -spec mutrec.clu -clu mutrec.clu
%
start_up = proc ()
    print_first_16("F", F)
    print_first_16("M", M)
  end start_up

% Print the first few values for F and M
print_first_16 = proc (name: string, fn: proctype (int) returns (int))
    po: stream := stream$primary_output()
    stream$puts(po, name || ":")
    for i: int in int$from_to(0, 15) do
        stream$puts(po, " " || int$unparse(fn(i)))
      end
    stream$putl(po, "")
  end print_first_16

F = proc (n: int) returns (int)
    if n = 0 then
        return (1)
      else
        return (n - M(F(n-1)))
      end
  end F

M = proc (n: int) returns (int)
    if n = 0 then
        return (0)
      else
        return (n - F(M(n-1)))
      end
  end M