''' Plist class is simply a wrapper for nodePS. It is initialized with a

PStructStor so OIDs can be made in somewhere. '''

def __init__(self, pstor):

''' Initialize with a PStructStor. All nodePS OIDs will be made in

that pstor '''

self.pstor = pstor

def cons(self, val, lnode):

return nodePS.make(self.pstor, value=val, nxt=lnode)

def car(self, lnode):

if not lnode:

raise ValueError("car: emptylist")

fields = nodePS.getfields(self.pstor, lnode)

return fields['value']

def cdr(self, lnode):

if not lnode:

raise ValueError("cdr: emptylist")

fields = nodePS.getfields(self.pstor, lnode)

return fields['nxt']

def plist(self, *args):

''' A plist constructor that takes variable number of values and make

them into a plist '''

if len(args) == 0:

return emptylist

return nodePS.make(self.pstor, value=args[0], nxt=self.plist(*args[1:]))

def liter(self, ll):

''' returns a generator of the linked list '''

while ll is not emptylist:

yield self.car(ll)

ll = self.cdr(ll)

def map(self, func, ll):

''' This map returns a "regular" list of Oids '''

if not ll:

return []

return [func(i) for i in self.liter(ll)]

def insertAfter(self, ll, compare, newvalue):

''' Inserts a new value @newvalue into a plist @ll after the

node whose value is equal to @compare. If @compare is not found then an

exception is raised. '''

stack = []

i = ll

while i:

found = self.car(i) == compare

stack.append(i)

i = self.cdr(i)

if found:

break

if not i:

# compare not found in ll

raise RuntimeError("compare value not found in list!")

newll = self.cons(newvalue, i)

while stack:

n = stack.pop()

newll = self.cons(self.car(n), newll)