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我已經寫了一些Go代碼在FP風格生成素數:爲什麼這個代碼失敗?
package main
import (
"fmt"
)
func gen_number_stream() func() (int, bool) {
i := 1
return func() (int, bool) {
i += 1
return i, true
}
}
func filter_stream(stream func() (int, bool), f func(int) bool) func() (int, bool) {
return func() (int, bool) {
for i, ok := stream(); ok; i, ok = stream() {
if f(i) {
return i, true
}
}
return 0, false
}
}
func sieve(stream func() (int, bool)) func() (int, bool) {
return func() (int, bool) {
if p, ok := stream(); ok {
remaining := filter_stream(stream, func(q int) bool { return q % p != 0 })
stream = sieve(remaining)
return p, true
}
return 0, false
}
}
func take(stream func() (int, bool), n int) func() (int, bool) {
return func() (int, bool) {
if n > 0 {
n -= 1
return stream()
}
return 0, false
}
}
func main() {
primes := take(sieve(gen_number_stream()), 50)
for i, ok := primes(); ok; i, ok = primes() {
fmt.Println(i)
}
}
當我運行這段代碼,它變得越來越慢,最後得到一個運行時錯誤是這樣的:
runtime: out of memory: [...]
這裏是Python代碼的一個版本,它運行良好:
def gen_numbers():
i = 2
while True:
yield i
i += 1
def sieve(stream):
p = stream.next()
yield p
for i in sieve(i for i in stream if i % p != 0):
yield i
def take(stream,n):
for i,s in enumerate(stream):
if i == 50: break
yield s
def main():
for i in take(sieve(gen_numbers()),50):
print i
if __name__ == '__main__':
main()
我想知道爲什麼以及如何解決它。這是我的代碼或golang編譯器的問題嗎? 謝謝!附:
PS:對不起,我的英文很差。
您能否爲stream2完成'....'? – VonC
http://play.golang.org/p/in9euT48_Z – Max
仍然不明白。我試過http://play.golang.org/p/LDtWC36c9V,但它不能正常工作 – VonC