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VList: Difference between revisions
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[6]
</pre>
=={{header|Nim}}==
{{trans|Go}}
<lang Nim>type
VSeg[T] = ref object
next: VSeg[T]
elems: seq[T]
VList[T] = ref object
base: VSeg[T]
offset: int
func newVList[T](): VList[T] = new(VList[T])
func `[]`[T](v: VList[T]; k: int): T =
## Primary operation 1: locate the kth element.
if k >= 0:
var i = k + v.offset
var sg = v.base
while not sg.isNil:
if i < sg.elems.len:
return sg.elems[i]
dec i, sg.elems.len
sg = sg.next
raise newException(IndexDefect, "index out of range; got " & $k)
func cons[T](v: VList[T]; a: T): VList[T] =
## Primary operation 2: add an element to the front of the VList.
if v.base.isNil:
return VList[T](base: VSeg[T](elems: @[a]))
if v.offset == 0:
let l2 = v.base.elems.len * 2
var elems = newSeq[T](l2)
elems[l2 - 1] = a
return VList[T](base: VSeg[T](next: v.base, elems: move(elems)), offset: l2 - 1)
dec v.offset
v.base.elems[v.offset] = a
result = v
func cdr[T](v: VList[T]): VList[T] =
## Primary operation 3: obtain a new array beginning at the second element of an old array.
if v.base.isNil:
raise newException(NilAccessDefect, "cdr on empty list")
if v.offset + 1 < v.base.elems.len:
inc v.offset
return v
result = VList[T](base: v.base.next, offset: 0)
func len[T](v: VList[T]): Natural =
## Primary operation 4: compute the length of the list.
if v.base.isNil: return 0
result = v.base.elems.len * 2 - v.offset - 1
func `$`[T](v: VList[T]): string =
if v.base.isNil: return "[]"
result = '[' & $v.base.elems[v.offset]
var sg = v.base
var sl = v.base.elems[v.offset+1..^1]
while true:
for e in sl: result.add ' ' & $e
sg = sg.next
if sg.isNil: break
sl = sg.elems
result.add ']'
proc printStructure[T](v: VList[T]) =
echo "offset: ", v.offset
var sg = v.base
while not sg.isNil:
echo " ", sg.elems
sg = sg.next
echo()
when isMainModule:
var v = newVList[string]()
echo "Zero value for type. Empty vList:", v
v.printStructure()
for a in countdown('6', '1'): v = v.cons($a)
echo "Demonstrate cons. Six elements added:", v
v.printStructure()
v = v.cdr()
echo "Demonstrate cdr. One element removed:", v
v.printStructure()
echo "Demonstrate length. Length = ", v.len()
echo()
echo "Demonstrate element access. v[3] = ", v[3]
echo()
v = v.cdr().cdr()
echo "Show cdr releasing segment. Two elements removed: ", v
v.printStructure()</lang>
{{out}}
<pre>Zero value for type. Empty vList:[]
offset: 0
Demonstrate cons. Six elements added:[1 2 3 4 5 6]
offset: 1
@["", "1", "2", "3"]
@["4", "5"]
@["6"]
Demonstrate cdr. One element removed:[2 3 4 5 6]
offset: 2
@["", "1", "2", "3"]
@["4", "5"]
@["6"]
Demonstrate length. Length = 5
Demonstrate element access. v[3] = 5
Show cdr releasing segment. Two elements removed: [4 5 6]
offset: 0
@["4", "5"]
@["6"]</pre>
=={{header|ooRexx}}==
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