斐波那契数在Haskell中 [英] Fibonacci Numbers in Haskell
问题描述
您好我需要将我的F#代码更改为Haskell代码,但我在Haskell中是如此新颖,我不能这样做我的代码只是从键盘读取数据,如果数据不是整数返回错误消息,则计算n斐波那契数然后写入列表之后,将列表写入txt文件这里是我的代码
打开系统
let rec fib n =
匹配n与
| 0-> 0
| 1-> 1
| 2-> 1
| n-> fib( N-1)+ FIB(N-2);;
让printFibonacci list =
为i = 0 to(List.length list)-1 do
printf%d(list.Item(i));;
let writeToFile list =
let file = System.IO.File.Create(C:\out2.txt)
let mutable s =
让writer = new System.IO.StreamWriter(file)
尝试
(对于i = 0)(List.length list)-1 do
s< --list.Item(i)。 ToString()
writer.Write(s +)
finally
writer.Close()
file.Dispose()
printfnWrited To文件
让mutable control = true
让mutable num = 0
while control do
try
printfn输入数字:
num < - Convert.ToInt32(stdin.ReadLine())
let listFibonacci = [for i in 0 .. num-1-> fib(i)]
printFibonacci(listFibonacci)
printfn\\\
%A(listFibonacci)
writeToFile(listFibonacci)
control< -false
with
| :? System.FormatException - > printfn数字格式异常;
Console.ReadKey true |>忽略
main = do putStrLn输入一个数字:
num < - readLn
fibs = map fib [0..n]
mapM'print fibs
然而,由于haskell是懒惰的,所以有一个巧妙的方法来定义所有斐波那契数列表。既然你想要这个列表的前缀,那么使用这个定义更自然(也更有效):
fibs = 0 :1:zipWith(+)fibs(tail fibs)
main = do putStrLn输入一个数字:
num < - readLn
mapM'print(take n fibs )
编辑:要写入文件而不是stdout,请替换 print
(\ num - > appendFilefilename(show num))或
(appendFilefilename。show)
。
Hi everbody I need to change my F# code to Haskell code but I am so new in Haskell and I can not this My code simply read data from keyboard if data not an integer return an error message then calculate the n fibonacci number then writes to a list after that writes the list into a txt file Here is my code
open System
let rec fib n =
match n with
|0->0
|1->1
|2->1
|n->fib(n-1)+fib(n-2);;
let printFibonacci list =
for i=0 to (List.length list)-1 do
printf "%d " (list.Item(i));;
let writeToFile list =
let file = System.IO.File.Create("C:\out2.txt")
let mutable s =""
let writer = new System.IO.StreamWriter(file)
try
for i=0 to (List.length list)-1 do
s <- list.Item(i).ToString()
writer.Write(s+" ")
finally
writer.Close()
file.Dispose()
printfn "Writed To File"
let mutable control = true
let mutable num = 0
while control do
try
printfn "Enter a Number:"
num <- Convert.ToInt32(stdin.ReadLine())
let listFibonacci = [for i in 0 .. num-1->fib(i)]
printFibonacci(listFibonacci)
printfn "\n%A"(listFibonacci)
writeToFile(listFibonacci)
control<-false
with
| :? System.FormatException->printfn "Number Format Exception";
Console.ReadKey true|>ignore
fib 0 = 0
fib 1 = 1
fib n = fib (n-1) + fib (n-2)
main = do putStrLn "Enter a number:"
num <- readLn
fibs = map fib [0..n]
mapM' print fibs
However since haskell is lazy there is a clever way to define the list of all fibonacci numbers. And since you want a prefix of that list, it's more natural to use this definition (also more efficient):
fibs = 0 : 1 : zipWith (+) fibs (tail fibs)
main = do putStrLn "Enter a number:"
num <- readLn
mapM' print (take n fibs)
Edit: To write to a file instead of stdout replace print
with (\num -> appendFile "filename" (show num))
or (appendFile "filename" . show)
.
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