# define a hash to count the unique elements in @arr
my %check;

# @check{@arr} is a hash slice. It gives to all of the 
# values in %check where the key is an element from @arr.
# This is a list and it's also an lvalue (i.e. you can 
# assign values to it.
# 
# (1) x @arr (and I've corrected this from the original
# version. Uses the 'x' operator as a list constructor.
# In a list context it creates a list containing its
# left operand repeated the number of times given by
# the right operand (which is a scalar). @arr in a scalar
# context gives the number of elements in @arr. Hence
# we get a list containing scalar(@arr) 1s.
#
# We then assign this list to the list of lvalues created
# by @check{@arr}. This assigns a 1 to each value associated
# with a key found %check. The keys of %check are given by
# @arr, therefore we effectively create a key/value pair
# in %check for each element of @arr where the key is the
# element of @arr and the value is 1. If any element of
# @arr occurs multiple times we assign to the relevant
# value in %check multiple times.
# 
# We can then use 'keys' to extract this list of keys. If
# all the elements of @arr are the same the list of keys
# in %create only has one element.

@check{@arr} = (1) x @arr;

print "All the same" if keys %check == 1;