为什么`take`返回大数[]，即使列表是无限的？

Question

I have a doubt on why Haskell couldn't handle the following line

Prelude> take 1000000000000 $ repeat ' '

That line of code will return:

""

Which is obviously not 1,000,000,000,000 spaces.

If I try one less zero, it will print a long time.

And the thing that bothers me the most is that if I just write

Prelude> repeat ' '

It will work, even being a lot of more zeros.

So, why couldn't Haskell just print for a long time like it did with the repeat alone?

Answer 1

Are you on a 32 bit system? I suspect 1000000000000 wraps Int into a negative number. It's equal to about 2^40 .

You can check what's going on by entering 1000000000000 :: Int .

take with a negative number just returns the empty list:

Prelude> take (- 1) [1,2,3]
[]

For reference, take only takes Int :

Prelude> :t take
take :: Int -> [a] -> [a]