# How do Racket's basic list functions compare to Python?
# Suppose I have this list:

my_list = [1, 2, 3, 4]

# Here are the two basic accessors:

def first(a_list):           # aka 'car'
    return a_list[0]

def rest(a_list):            # aka 'cdr'
    return a_list[1:]

print( first(my_list) )
print( rest(my_list) )

# Racket provides named list accessors for the first ten items in
# a list: first, second, ... tenth.  It also provides a position-
# based function, list-ref, for accessing list items as if they
# were in an array.
#
# In Python, lists *are* variable-length arrays.
# In Racket, lists are linked lists.

# What about cons?  Python makes it easy to add items to the end:
#    my_list.append(0)
#
# In Racket, we add to the front of a list, not the back.
# Here is cons:

def cons(item, a_list):
    return [item] + a_list

print( cons(0, my_list) )

# In Python, we might also use
#    a_list.insert(0, item)
# but that *changes* a_list.  cons does not change its list!