Haskell调试

Question

如何在每次调用时打印haskell中的列表或内容,例如:

funct a list = funct (a + 1) (a : list) 
               print list here ??????? but how ? 

Answer 1

对于调试,有

import Debug.Trace

funct :: Integer -> [Integer] -> Bool 
funct a list = trace (show list) $ funct (a + 1) (a : list)

哪里trace :: String -> a -> a.它unsafePerformIO在引擎盖下使用,所以它是邪恶的,仅用于调试.

请注意,由于延迟评估,调试输出可能会以令人惊讶的顺序出现,并与程序通常会生成的输出交错.

同

module TraceIt where

import Debug.Trace

funct :: Integer -> [Integer] -> Bool
funct 10 list = null list
funct a list = trace (show list) $ funct (a + 1) (a : list)

我明白了

*TraceIt> funct 1 []
[]
[1]
[2,1]
[3,2,1]
[4,3,2,1]
[5,4,3,2,1]
[6,5,4,3,2,1]
[7,6,5,4,3,2,1]
[8,7,6,5,4,3,2,1]
False

正如所料.