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Minor cleanup. This is pretty nice. 

It's hard to believe this datastructure is so obscure!
This commit is contained in:
Simon Forman 2023-02-16 11:45:54 -08:00
parent a6a2c2d955
commit 55b48a0655
1 changed files with 28 additions and 31 deletions
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59
vlist.py
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@ -13,25 +13,6 @@ a Pointer to a VList is a pair of (VList and offset).
''' '''
def new_VList(base=(), offset=0, size=1):
assert size >= 1
return (base, offset, size, [0], [None] * length)
# In Fig 2 a list has been created with the integers (8,7,6,5,4,3)
o1 = ((), 0, 1, [1], [3])
o2 = (o1, 0, 2, [2], [4, 5])
o3 = (o2, 1, 4, [3], [6, 7, 8, None])
p0 = (o3, 2) # points to 8
p1 = (o3, 0) # points to 6
# cons(9, p1) = o4
o4 = (o3, 0, 1, [1], [9])
p2 = (o4, 0) # points to 9
def cons(thing, vlist_ptr): def cons(thing, vlist_ptr):
if not vlist_ptr: if not vlist_ptr:
@ -62,16 +43,10 @@ def cons(thing, vlist_ptr):
entry can now be made and additional elements added. entry can now be made and additional elements added.
''' '''
# Is this where we increase the size x 2? # Is this where we increase the size x 2?
size <<= 1 ; l = [None] * size ; l[0] = thing size <<= 1 ; l = [None] * size ; l[0] = thing
return (vlist_ptr[0], pointer_offset, size, [1], l), 0 return (vlist_ptr[0], pointer_offset, size, [1], l), 0
#return (vlist_ptr[0], pointer_offset, 1, [1], [thing]), 0
#p3 = cons(10, p0)
def head(vlist_ptr): def head(vlist_ptr):
if not vlist_ptr: if not vlist_ptr:
@ -94,10 +69,8 @@ def iter_vlist(vlist_ptr):
vlist_ptr = tail(vlist_ptr) vlist_ptr = tail(vlist_ptr)
##for i, p in enumerate((p0, p1, p2, p3)): def repr_vlist(vlist_ptr):
## print(f'p{i}') return ' '.join(map(str, iter_vlist(vlist_ptr)))
## print(' '.join(map(str, iter_vlist(p))))
## print()
p = () p = ()
@ -107,8 +80,32 @@ p = cons(5, p) ; print(p)
p = cons(6, p) ; print(p) p = cons(6, p) ; print(p)
p = cons(7, p) ; print(p) p = cons(7, p) ; print(p)
p = cons(8, p) ; print(p) p = cons(8, p) ; print(p)
print(' '.join(map(str, iter_vlist(p)))) print(repr_vlist(p))
assert p[0] == o3
# There is no such thing as a vlist_ptr with a null () vlist. That's an invariant. # There is no such thing as a vlist_ptr with a null () vlist. That's an invariant.
## # In Fig 2 a list has been created with the integers (8,7,6,5,4,3)
##
## o1 = ((), 0, 1, [1], [3])
## o2 = (o1, 0, 2, [2], [4, 5])
## o3 = (o2, 1, 4, [3], [6, 7, 8, None])
##
## p0 = (o3, 2) # points to 8
## p1 = (o3, 0) # points to 6
##
## # cons(9, p1) = o4
##
## o4 = (o3, 0, 1, [1], [9])
## p2 = (o4, 0) # points to 9
##
##
## p3 = cons(10, p0)
##for i, p in enumerate((p0, p1, p2, p3)):
## print(f'p{i}')
## print(' '.join(map(str, iter_vlist(p))))
## print()