length [c | x <- [1..100], let c = chain x, length c > 15] 16.02.2011 12:19, Tako Schotanus пишет:

Hello,

I was going through some of the tuturials and trying out different (syntactic) alternatives to the given solutions and I I got to this line:

*length [chain x | x <- [1..100] , length (chain x) > 15]*

Now, there's nothing wrong with it, it works of course. But the application of chain x is repeated twice and I wondered if there was a way for a guard in a list comprehension to refer to the item being produced?

Like this for example (invented syntax):

*length [@c(chain x) | x <- [1..100] , length c > 15]*

NB: Just to make clear, I'm not asking if there is an alternative way of preventing the repetition, of course there is, I'm just wondering about this very specific case within list comprehensions.

-Tako

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On 16 February 2011 09:19, Tako Schotanus wrote:

I wondered if there was a way for a guard in a list comprehension to refer to the item being produced?

I'm just wondering about this very specific case

Then, the answer is no. As others have noted, let binding is the way to go. Ozgur