$ perl -e'@a=qw(-1 -2 -3 -4 -5); 
          $max=0; 
          printf "Answer allegedly is %d\n",map { $max=($max < $_ ?  $_ : $max )} @a;'
Answer allegedly is 0

$ perl -e'@a=qw(-1 -2 -3 -4 -5); 
          $max=$a[0]; # Or shift @a, if you can be destructive
          printf "Answer allegedly is %d\n",map { $max=($max < $_ ?  $_ : $max )} @a;'
Answer is -1