loops - 如何在haskell中使用do和while循环

Question

我尝试使用添加并打印每个步骤，但它不起作用，有人可以帮助我吗？

addition x = x+1
acc_addition xs = do print xs
                     let result = addition xs
                         if result == 5
                            then return ()
                            else do
                                 print result
                                 addition result

Answer 1

你已经很接近了，你只需要打电话acc_addition而不是addition最后一步。从语法上讲，您还需要一个inforlet语句：

addition x = x+1
acc_addition xs = do print xs
                     let result = addition xs in
                         if result == 5
                            then return ()
                            else do
                                 print result
                                 acc_addition result

通过以下方式运行时ghci：

*Main> acc_addition 1
1
2
2
3
3
4
4

它打印两次的原因当然是你有两个打印语句。