c:\@Work\Perl>perl -wMstrict -le
"my $operators = '+-*/';
 my %disp =
   map { $_ => eval qq{ sub { return \$_[0] $_ \$_[1] } } }
   split '', $operators
   ;
 my $int = qr{ [-+]? \d+        }xms;
 my $op  = qr{ [\Q$operators\E] }xms;
 ;;
 my $t = 'foo 1  + 2 bar 34*56 baz 3-  4 and 56  /78 too';
 ;;
 for my $s ($t, @ARGV) {
   print '';
   print qq{'$s'};
   $s =~ s{ ($int) \s* ($op) \s* ($int) }{ $disp{$2}->($1, $3) }xmsge;
   print qq{'$s'};
   }
"  "x-3--4,-3++4"  "foo+bar"

'foo 1  + 2 bar 34*56 baz 3-  4 and 56  /78 too'
'foo 3 bar 1904 baz -1 and 0.717948717948718 too'

'x-3--4,-3++4'
'x1,1'

'foo+bar'
'foo+bar'