- Added the Array .differences(n=1) method.

It returns the n-th differences of the array (calling `sub`).

Example:

	var a = [43, 97, 128, 999]

	say a.diffs			#=> [54, 31, 871]
	say a.diffs(2)			#=> [-23, 840]
	say a.diffs(3)			#=> [863]

- Added the Array `acc` and `acc_by` aliases for methods `accumulator` and `accumulator_by`.

lib/Sidef/Types/Array/Array.pm

@@ -2250,6 +2250,8 @@ package Sidef::Types::Array::Array {
         bless \@acc, ref($self);
     }
 
+    *acc_by = \&accumulate_by;
+
     sub accumulate {
         my ($self, $block) = @_;
 
@@ -2272,6 +2274,28 @@ package Sidef::Types::Array::Array {
         bless \@acc, ref($self);
     }
 
+    *acc = \&accumulate;
+
+    sub differences {
+        my ($self, $n) = @_;
+
+        if (defined($n)) {
+            $n = CORE::int($n);
+        }
+        else {
+            $n = 1;
+        }
+
+        foreach my $i (1 .. $n) {
+            $self = $self->map_cons(2, Sidef::Types::Block::Block->new(code => sub { $_[1]->sub($_[0]) }));
+        }
+
+        $self;
+    }
+
+    *diffs           = \&differences;
+    *nth_differences = \&differences;
+
     sub reduce {
         my ($self, $obj, $initial) = @_;
 

lib/Sidef/Types/Array/Array.pod

@@ -260,20 +260,24 @@ Aliases: I<abbreviations>
 
 =cut
 
-=head2 accumulate
+=head2 acc
 
-Array.accumulate() -> I<Obj>
+Array.acc() -> I<Obj>
 
 Return the
 
+Aliases: I<accumulate>
+
 =cut
 
-=head2 accumulate_by
+=head2 acc_by
 
-Array.accumulate_by() -> I<Obj>
+Array.acc_by() -> I<Obj>
 
 Return the
 
+Aliases: I<accumulate_by>
+
 =cut
 
 =head2 all
@@ -670,6 +674,16 @@ Return the
 
 =cut
 
+=head2 diffs
+
+Array.diffs() -> I<Obj>
+
+Return the
+
+Aliases: I<differences>, I<nth_differences>
+
+=cut
+
 =head2 dig
 
 Array.dig() -> I<Obj>