[m-rev.] diff: additions to the integer module

[Julien Fischer]

Additions to the integer module.

library/integer.m:
 	Add some more functions that return constants: negative_one/0 and ten/0.

 	Export (and rename) the predicate that is used to test whether an integer
 	is equal to zero.

NEWS:
 	Announce the above (and also two/0, which was added recently).

Julien.


diff --git a/NEWS b/NEWS
index eb6f7f2..ffcf4cd 100644
--- a/NEWS
+++ b/NEWS
@@ -110,6 +110,8 @@ Changes to the Mercury standard library:
     - to_int/2
     - det_to_int/1
     - to_base_string/2
+   - negative_one/0, two/0, ten/0
+   - is_zero/1

    The following functions in the integer module have been deprecated:

diff --git a/library/integer.m b/library/integer.m
index fe3d5b2..7f8d813 100644
--- a/library/integer.m
+++ b/library/integer.m
@@ -185,6 +185,19 @@
  :- func int(integer) = int.
  :- pragma obsolete(int/1).

+    % True if the argument is equal to integer.zero.
+    %
+:- pred is_zero(integer::in) is semidet.
+
+%---------------------------------------------------------------------------%
+%
+% Constants.
+%
+
+    % Equivalent to integer(-1).
+    %
+:- func negative_one = integer.
+
      % Equivalent to integer(0).
      %
  :- func zero = integer.
@@ -197,6 +210,10 @@
      %
  :- func two = integer.

+    % Equivalent to integer(10).
+    %
+:- func ten = integer.
+
  %---------------------------------------------------------------------------%
  %---------------------------------------------------------------------------%

@@ -416,10 +433,6 @@ neg_list([H | T], [-H | NT]) :-

  big_isnegative(i(Sign, _)) :- Sign < 0.

-:- pred big_iszero(integer::in) is semidet.
-
-big_iszero(i(0, [])).
-
  :- func big_neg(integer) = integer.

  big_neg(i(S, Digits0)) = i(-S, Digits) :-
@@ -468,7 +481,7 @@ big_mod(X, Y) = Mod :-
  :- func big_right_shift(integer, int) = integer.

  big_right_shift(X, I) =
-    ( big_iszero(X) ->
+    ( is_zero(X) ->
          X
      ; big_isnegative(X) ->
          \ pos_right_shift(\ X, I)
@@ -505,7 +518,7 @@ rightshift(Mod, InvMod, i(Len, [H | T]), Carry) = Integer :-
  :- func big_left_shift(integer, int) = integer.

  big_left_shift(X, I) =
-    ( big_iszero(X) ->
+    ( is_zero(X) ->
          X
      ; big_isnegative(X) ->
          big_neg(pos_left_shift(big_neg(X), I))
@@ -672,9 +685,9 @@ pos_cmp(X, Y) = Result :-
  :- func big_plus(integer, integer) = integer.

  big_plus(X, Y) = Sum :-
-    ( X = integer.zero ->
+    ( is_zero(X) ->
          Sum = Y
-    ; Y = integer.zero ->
+    ; is_zero(Y) ->
          Sum = X
      ;
          AbsX = big_abs(X),
@@ -923,9 +936,9 @@ pos_mul_list([X | Xs], Carry, Y) =
      integer::out) is det.

  big_quot_rem(X, Y, Quot, Rem) :-
-    ( big_iszero(Y) ->
+    ( is_zero(Y) ->
          throw(math.domain_error("integer.big_quot_rem: division by zero"))
-    ; big_iszero(X) ->
+    ; is_zero(X) ->
          Quot = integer.zero,
          Rem  = integer.zero
      ;
@@ -1182,11 +1195,24 @@ integer.int(Integer) = integer.det_to_int(Integer).
  int_list([], Accum) = Accum.
  int_list([H | T], Accum) = int_list(T, Accum * base + H).

-integer.zero = i(0, []).
+%---------------------------------------------------------------------------%
+
+is_zero(i(0, [])).
+
+%---------------------------------------------------------------------------%
+%
+% Constants.
+%
+
+negative_one = i(-1, [-1]).
+
+zero = i(0, []).
+
+one = i(1, [1]).

-integer.one = i(1, [1]).
+two = i(1, [2]).

-integer.two = i(1, [2]).
+ten = i(1, [10]).

  %---------------------------------------------------------------------------%
  %