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Minor cleanup.

This commit is contained in:
Simon Forman 2023-03-18 11:31:12 -07:00
parent e39b9460bb
commit d735d00016
1 changed files with 17 additions and 38 deletions
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53
vlist.py
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@ -22,33 +22,16 @@ def cons(thing, vlist_ptr):
vlist, pointer_offset = vlist_ptr vlist, pointer_offset = vlist_ptr
base, _offset, size, last_used_list, data = vlist base, _offset, size, last_used_list, data = vlist
[last_used] = last_used_list # Note that we could do this pattern last_used = last_used_list[0]
# matching directly in the assignment statement on the previous line, # Note that we want to keep that length-one list "last_used_list"
# however, we want to keep that length-one list "last_used_list"
# around so we can mutate the last_used value of "vlist". # around so we can mutate the last_used value of "vlist".
'''
During the consing of (9) the pointer offset is compared with the
last used offset, LastUsed. If it is the same and less than the block
size then it is simply incremented, the new entry made and LastUsed
updated.
'''
if pointer_offset == last_used - 1 and last_used < size: if pointer_offset == last_used - 1 and last_used < size:
pointer_offset += 1 pointer_offset += 1
data[pointer_offset] = thing data[pointer_offset] = thing
last_used_list[0] += 1 last_used_list[0] += 1
return vlist, pointer_offset return vlist, pointer_offset
'''
If on the other-hand the pointer offset is less than the LastUsed a
cons is being applied to the tail of a longer list, as is the case
with the (9). In this case a new list block must be allocated and its
Base-Offset pointer set to the tail contained in the original list.
The offset part being set to the point in tail that must be extended.
The new 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 size <<= 1
offset = 0 offset = 0
@ -95,15 +78,15 @@ def pick(n, vlist_ptr):
''' '''
assert n >= 0 assert n >= 0
if not vlist_ptr: if not vlist_ptr:
raise ValueError("Empty list!") raise ValueError('Empty list!')
vlist, pointer_offset = vlist_ptr vlist, pointer_offset = vlist_ptr
q = pointer_offset - n n = pointer_offset - n
while q < 0: while n < 0:
if not vlist: if not vlist:
raise ValueError(f'Pick index {n} greater than length of list.') raise ValueError('Pick index greater than length of list.')
vlist, offset = vlist[:2] vlist, offset = vlist[:2]
q += offset + 1 # Offsets in the paper count from one, not zero? n += offset + 1 # Offsets in the paper count from one, not zero?
return vlist[-1][q] return vlist[-1][n]
def length(vlist_ptr): def length(vlist_ptr):
@ -116,21 +99,17 @@ def length(vlist_ptr):
return n return n
if __name__ == '__main__':
p = ()
for n in range(16):
p = cons(n, p)
#print(p)
p = () print(repr_vlist(p))
p = cons(3, p)# ; print(p)
p = cons(4, p)# ; print(p)
p = cons(5, p)# ; print(p)
p = cons(6, p)# ; print(p)
p = cons(7, p)# ; print(p)
p = cons(8, p)# ; print(p)
print(repr_vlist(p)) for n in range(length(p)):
for n in range(length(p)):
print(pick(n, p), end=' ') print(pick(n, p), end=' ')
print()
print()