1:- module(thousands, [n/2,n/3,n/4]).    2:- use_module(library(function_expansion)).    3
    4% The following definitions for n/{2,3,4} are strictly for the
    5% documentation system.  These macros are expanded away.

 n(Thousands, Hundreds:integer)

Represents an integer less than 1 million.

   10n(_,_).

 n(Millions, Thousands, Hundreds:integer)

Represents an integer less than 1 billion.

   15n(_,_,_).

 n(Billions, Millions, Thousands, Hundreds:integer)

Represents an integer less than 1 trillion.

   20n(_,_,_,_).
   21
   22user:function_expansion(n(Thousands,Ones), X, true) :-
   23    calc_n(0, 0, Thousands, Ones, X).
   24
   25user:function_expansion(n(Millions,Thousands,Ones), X, true) :-
   26    calc_n(0, Millions, Thousands, Ones, X).
   27
   28user:function_expansion(n(Billions,Millions,Thousands,Ones), X, true) :-
   29    calc_n(Billions, Millions, Thousands, Ones, X).
   30
   31calc_n(Billions, Millions, Thousands, Ones, X) :-
   32    integer(Billions),
   33    integer(Millions),
   34    integer(Thousands),
   35    integer(Ones),
   36    X is 1000000000*Billions + 1000000*Millions + 1000*Thousands + Ones.
   37
   38:- begin_tests(thousands).   39test(billions) :-
   40    1123456789 =:= n(1,123,456,789).
   41test(millions) :-
   42    123456789 =:= n(123,456,789).
   43test(thousands) :-
   44    123456 =:= n(123,456).
   45
   46test(nested) :-
   47    a(9876,b(1234),c(d(6542))) = a(n(9,876),b(n(1,234)),c(d(n(6,542)))).
   48
   49test(variable) :-
   50    X = n(9,876,543),
   51    9876543 =:= X.
   52
   53test(hundreds_not_expanded) :-
   54    n(123) =.. [n, 123].
   55test(variables_not_expanded) :-
   56    n(A,123) =.. [n, A, 123].
   57:- end_tests(thousands).