089.对函数的递归

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本文介绍了一个使用Ada语言实现的阶乘程序，通过定义阶乘函数和判断阶乘是否可能的辅助函数，展示了从-2到5的整数阶乘计算过程，并通过具体数值验证了函数的正确性。

with Ada.Text_IO,Ada.Integer_Text_IO;
use Ada.Text_IO,Ada.Integer_Text_IO;

procedure FuncRecr is
   
   START :constant :=-2;
   STOP  :constant :=5;
   Result:Integer;
   Data_Value:Integer;
   
   function Factorial_Possible(Number:Integer)return Boolean;
   
   function Factorial(Number :Integer)return Integer is
   begin
      if not Factorial_Possible(Number)then
         Put("Factorial not possible for");
         Put(Number,4);
         New_Line;
         return 0;
      end if;
      if Number =0 then
         return 1;
      elsif Number =1 then
         return 1;
      else
         return Factorial(Number-1)*Number;
      end if;
   end Factorial;
   
   
   function Factorial_Possible(Number:Integer)return Boolean is
   begin
      if Number >=0 then
         return TRUE;
      else
         return FALSE;
      end if;
   end Factorial_Possible;
   
begin
   Put("Factorial program!");
   New_Line(2);
   
   for Number_To_Try in START..STOP loop
      Put(Number_To_Try,3);
      if Factorial_Possible(Number_To_Try) then
         Result:=Factorial(Number_To_Try);
         Put(" is legal to factorialize and the result is!");
         Put(Result,6);
      else
         Put(" is not legal to factoialize");
      end if;
      New_Line;
   end loop;
   
   New_Line;
   Data_Value:=4;
   Result:=Factorial(2-Data_Value);
   Result:=Factorial(Data_Value+3);
   Result:=Factorial(2*Data_Value-3);
   Result:=Factorial(Factorial(3));
   Result:=Factorial(4);
   Result:=Factorial(0);
   
end FuncRecr;