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discard """
output: '''start
false
0
1
2
end
@[2, 4, 6, 8, 10]
@[4, 8, 12, 16, 20]'''
"""
# bug #3837
proc iter1(): (iterator: int) =
let coll = [0,1,2]
result = iterator: int {.closure.} =
for i in coll:
yield i
proc iter2(it: (iterator: int)): (iterator: int) =
result = iterator: int {.closure.} =
echo finished(it)
for i in it():
yield i
echo "start"
let myiter1 = iter1()
let myiter2 = iter2(myiter1)
for i in myiter2():
echo i
echo "end"
# start
# false
# end
from sequtils import toSeq
type Iterable*[T] = (iterator: T) | Slice[T]
## Everything that can be iterated over, iterators and slices so far.
proc toIter*[T](s: Slice[T]): iterator: T =
## Iterate over a slice.
iterator it: T {.closure.} =
for x in s.a..s.b:
yield x
return it
proc toIter*[T](i: iterator: T): iterator: T =
## Nop
i
iterator map*[T,S](i: Iterable[T], f: proc(x: T): S): S =
let i = toIter(i)
for x in i():
yield f(x)
proc filter*[T](i: Iterable[T], f: proc(x: T): bool): iterator: T =
## Iterates through an iterator and yields every item that fulfills the
## predicate `f`.
##
## .. code-block:: nim
## for x in filter(1..11, proc(x): bool = x mod 2 == 0):
## echo x
let i = toIter(i)
iterator it: T {.closure.} =
for x in i():
if f(x):
yield x
result = it
iterator filter*[T](i: Iterable[T], f: proc(x: T): bool): T =
let i = toIter(i)
for x in i():
if f(x):
yield x
var it = toSeq(filter(2..10, proc(x: int): bool = x mod 2 == 0))
echo it # @[2, 4, 6, 8, 10]
it = toSeq(map(filter(2..10, proc(x: int): bool = x mod 2 == 0), proc(x: int): int = x * 2))
echo it # Expected output: @[4, 8, 12, 16, 20], Actual output: @[]
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