我试图使用一个可能包含以下类型元素的无限列表：
#include< stdio.h>
#include< string.h>
#include< stdlib.h>
#include< process.h>
//USER-DEFINED FUNCTIONS
char top_down();
char copy_function();
char compare_function();
//char adder_function();
void header(void);
#define MAX 1000
void header()
{
printf("*-*-*-*-*TASK_PERFORMER*-*-*-*-*");
printf("\n\n");
}
//PROGRAM STARTS HERE
main()
{
//VARIABLE DECLARATION
char x =
{ 0 };
//HEADING FUNCTION
header();
//USER-DEFINED FUNCTION CONSISTING OF ALL INPUTS.
top_down();
//TERMINAL-PAUSE
system("pause");
}
char top_down()
{
char s1[MAX] =
{ 0 }, s2[MAX] =
{ 0 }, x =
{ 0 };
printf("Enter the First String : \n");
fgets(s1, MAX, stdin);
printf("\n");
printf("The Entered First String : \n");
printf("%s", s1);
printf("\n");
printf("Enter the Second String : \n");
fgets(s2, MAX, stdin);
printf("\n");
printf("The Entered Second String : \n");
printf("%s", s2);
printf("\n");
printf("*-*-*-TYPE ANY OPTION TO PERFORM TASK-*-*-*");
printf("\n");
//GIVEN OPTIONS FOR SELECTOR
printf("Enter one option from the following : \n\n");
printf("(a) To Copy one string to another. \n");
printf("(b) To Compare two string. \n");
printf("(c) To Add a string to the end of another string. \n");
printf("\n");
repeat:
printf("Enter Your Option : \n");
scanf_s("%c", &x);
printf("\n");
//OPTION-SELECTOR
switch (x)
{
case 'a':
copy_function(s1, s2);
break;
case 'b':
compare_function(s1, s1);
break;
case 'c':
//adder_function(s1, s2);
break;
default:
printf("INVALID OPTION \n");
printf("Please Try Again \n");
goto repeat;
break;
return;
}
}
char copy_function(char s_1[], char s_2[])
{
int x = 0;
x = strlen(s_2);
printf("Second String will be copied to First string now \n");
//strcpy(s_1, s_2);
strcpy_s(s_1, x, s_2);
printf("\n");
printf("First String Output : \n");
printf("%s", s_1);
return;
}
char compare_function(char s_1[], char s_2[])
{
int a = 0, l1 = 0, l2 = 0, i = 0;
printf("First String will be compared to Second String now \n ");
//printf("\n");
if (strcmp(s_1, s_2) == 0)
printf("Both String are equal to each other \n");
else if (strcmp(s_1, s_2) > 0)
printf("First String is greater than Second String");
else
printf("First String is lesser than Second String \n");
return;
}
IO (Either Throwable a)类型的元素感兴趣。 Right个元素始终是第一个，然后是Right个元素问题在于我使用的实现是错误的，因为函数Left评估无限列表，因此函数永远不会结束。
sequence有关如何正确使用该列表的任何想法？
答案 0 :(得分：2)
是的，这不适用于sequence
您需要执行类似
的操作takeWhileRight (x:xs) = do
y <- x
case y of
Right -> (y:) <$> takeWhileRight xs
Left -> pure []
takeWhileRight [] = pure []
（未测试）。
请注意，仍然必须运行提供Left的第一个IO操作。这是不可避免的。