On 2007-01-18, sturlamolden <[EMAIL PROTECTED]> wrote:
>
> Paul Rubin wrote:
>
>> But that's what Lisp does too.
>
> Ok, I may have to reread Paul Graham's book on ANSI Common Lisp
> then.
Here's something silly I whipped up to play with.
r""" Lisp style singly-linked lists called llist.
"""
def consp(o):
return isinstance(o, Cons)
def car(c):
""" Return the car of a lisp-list. Undefined for nil. """
if null(c):
raise AttributeError("nil has no cdr")
return c.car
def cdr(c):
""" Return the cdr of a lisp=list. """
if null(c):
return nil
return c.cdr
def cons(o, c):
""" Build a new cons cell from an object and a Cons. """
return Cons(o, c)
def null(c):
return c is nil
def rplaca(c, o):
c.car = o
return c
def rplacd(c, o):
c.cdr = o
return c
def llist(li):
""" Build a llist from a list. """
c = nil
for a in reversed(li):
if isinstance(a, list):
c = cons(llist(a), c)
else:
c = cons(a, c)
return c
class Cons(object):
def __init__(self, car, cdr):
self.car = car
self.cdr = cdr
def __repr__(self):
def helper(li, s):
if null(li):
return s + ")"
else:
return helper(cdr(li), s + " %s" % repr(car(li)))
return helper(self.cdr, "(" + repr(self.car))
class Nil(Cons):
def __init__(self):
Cons.__init__(self, None, None)
def __repr__(self):
return '()'
nil = Nil()
print cons(5, nil)
print cons(5, cons(3, nil))
print cons(cons(5, (cons(7, nil))), cons(cons(5, cons(3, nil)), nil))
print nil
print llist([1, ['a', 'b', 'c'], 2, 3])
There's lots more more stuff to add, but the fun wore out. I'd
like if it the cdr of nil could actually be nil, instead of None
with a special case in cdr, but I couldn't figure out a neat way
to do it.
--
Neil Cerutti
I've had a wonderful evening, but this wasn't it. --Groucho Marx
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