如何在ABAP里用函数式编程思想打印出非波拉契Fibonacci（数列）

在JavaScript里能够用ES6提供的FunctionGenerator这种黑科技来打印非波拉契数列，具体细节参考我这篇文章。

在ABAP里也有不少种方式实现这个需求。

下面这个report分别用递归和ABAP internal table的方式实现了非波拉契数列的打印。

REPORT Z_FIBO.

PARAMETERS: N type i,

v1 RADIOBUTTON GROUP v default 'X',

v2 RADIOBUTTON GROUP v.

data: f type i,

t type i.

data: product_guid type comm_product-product_guid.

get run time field t.

case 'X'.

when v1\. perform fibonacci using n changing f.

when v2\. perform fibonacci_2 using n changing f.

endcase.

write: / 'Fibonacci(', n, ') =', f.

get run time field t.

write: / 'Runtime', t, 'microseconds'.

*&---------------------------------------------------------------------*

*& Form fibonacci

*&---------------------------------------------------------------------*

form fibonacci using in type i

changing fib type i.

data: f_1 type i, f_2 type i,

n_1 type i, n_2 type i.

case in.

when 0\. fib = 1.

when 1\. fib = 1.

when others.

n_1 = in - 1.

n_2 = in - 2.

perform fibonacci using n_1 changing f_1.

perform fibonacci using n_2 changing f_2.

fib = f_1 + f_2.

endcase.

endform. "fibonacci

*&---------------------------------------------------------------------*

*& Form fibonacci_2

*&---------------------------------------------------------------------*

form fibonacci_2 using in type i

changing fib type i.

data: f_1 type i, f_2 type i,

n_1 type i, n_2 type i,

l type i.

data: fibo type table of i.

append 1 to fibo. " fibonacci(0)

append 1 to fibo. " fibonacci(1)

n_1 = 1.

n_2 = 2.

l = in - 1.

do l times.

read table fibo index n_1 into f_1.

read table fibo index n_2 into f_2.

fib = f_1 + f_2.

add 1 to n_1\. add 1 to n_2.

append fib to fibo.

enddo.

endform. "fibonacci_2