[Haskell-cafe] Noob question about list comprehensions
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 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Noob question about list comprehensions
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 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Noob question about list comprehensions
Might better ways, but the following work: length [c | x - [1..100], let c = chain x , length c 15] length [c | x - [1..100], c - [chain x] , length c 15] On Wed, Feb 16, 2011 at 9:19 AM, Tako Schotanus t...@codejive.org wrote: 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 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Noob question about list comprehensions
On 16 February 2011 09:19, Tako Schotanus t...@codejive.org 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 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Noob question about list comprehensions
Ok, thanks all, that was what I was looking for :) -Tako On Wed, Feb 16, 2011 at 10:46, Ozgur Akgun ozgurak...@gmail.com wrote: On 16 February 2011 09:19, Tako Schotanus t...@codejive.org 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 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
