Re: [Haskell-cafe] Producing MinimumValue
2007/7/19, Jason Dagit [EMAIL PROTECTED]: I prefer, allEqual [] = True allEqual xs = foldl1 (==) xs But, unfortunately, it's not a one liner like yours (unless you allow allEqual [] = undefined). Oh and silly me, that only works for [Bool]. My natural instinct is, allEqual [] = True allEqual (x:xs) = all (== x) xs with the same caveat about allEqual [] as in your case. - Benja ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re[2]: [Haskell-cafe] Producing MinimumValue
Hello Benja, Friday, July 20, 2007, 6:10:15 PM, you wrote: My natural instinct is, allEqual [] = True allEqual (x:xs) = all (== x) xs with the same caveat about allEqual [] as in your case. allEqual xs = all (== head xs) xs -- Best regards, Bulatmailto:[EMAIL PROTECTED] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Re[2]: [Haskell-cafe] Producing MinimumValue
2007/7/20, Bulat Ziganshin [EMAIL PROTECTED]: allEqual [] = True allEqual (x:xs) = all (== x) xs with the same caveat about allEqual [] as in your case. allEqual xs = all (== head xs) xs Rght. Not evaluated in the edge case, because xs is empty. Didn't think of that, nice :-) - Benja ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Producing MinimumValue
The question suggests to use some functions defined in the section, and one of them is iSort. So i used the function but without using higher-order functions - i don't know though how correct is it? minimumValue :: [Int] - Int minimumValue ns = head (iSort ns) The other question is to test whether the values of allEqual on inputs 0 to n are all equal. Again, I defined the method but not sure if its concise? allEqual :: [Int] - Bool allEqual xs = length xs == length (filter isEqual xs) where isEqual n = (head xs) == n Excuse me for questions like these, probably they are not interested ones but I am just trying to learn the thinking behind the function definitions. Thank you Joachim Breitner-2 wrote: Hi, Am Mittwoch, den 18.07.2007, 13:42 -0700 schrieb Alexteslin: I am trying to define a function as part of the exercises that gives a result of a minimum value of the input list of ints. Such as this: minimumValue :: [Int] - Int minimumValue ns ... using either filter or map functions but Not foldr1, because the exercise precedes the section on foldr1. I am confused because using filter - it generates a list on some constraint function for each element. Any hints will be very appreciated. Thank you Are you allowed to define the function without any of filter or map, just yourself? minimumValue [a] = ... minimumValue (x:xs) = .. x .. minimumValue xs .. Greetings, Joachim -- Joachim Breitner e-Mail: [EMAIL PROTECTED] Homepage: http://www.joachim-breitner.de ICQ#: 74513189 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- View this message in context: http://www.nabble.com/Producing-MinimumValue-tf4106379.html#a11694422 Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Producing MinimumValue
You can get the head and the tail by pattern matching. Lets say you have a function that takes a list: myfunction list = -- do something here go = myfuction [1,4,2,6] ... you can write the list bit of the function as (x:xs), where x is the head, or first element, of the list, and xs is the tail, or the rest of the list: myfunction (x:xs) = -- do something here then you can call myfunction on xs, and compare that to x, to give the result. This is recursive: the function calls itself over and over again, until at some point it's going to execute myfuction [] or myfunction [6], which is easy to handle, for example by adding the definition: myfunction [a] = -- the value of myfunction given a Go here for a really great tutorial: http://www.cs.nott.ac.uk/~gmh/book.html Recursive functions are in slides, number 6, but the tutorials are really great: just start from 1 and work your way through. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Producing MinimumValue
On Thu, 19 Jul 2007 10:55:19 -0700 (PDT), you wrote: The question suggests to use some functions defined in the section, and one of them is iSort. Aha. Well, that one certainly lends itself better to this particular proplen than either map or filter. minimumValue :: [Int] - Int minimumValue ns = head (iSort ns) If I were going to use a sort, then yes, that's the way I would do it. Of course, sorting isn't the best way to solve the problem, as sorting will always be at least O(n * log n), whereas a more straightforward algorithm would be O(n). The other question is to test whether the values of allEqual on inputs 0 to n are all equal. Again, I defined the method but not sure if its concise? allEqual :: [Int] - Bool allEqual xs = length xs == length (filter isEqual xs) where isEqual n = (head xs) == n Simple recursion is probably the most conceptually straightforward approach here. One little difficulty with this problem (and with minimumValue, too) is that the problem isn't completely specified, because we don't know what answer we're supposed to give when the list is empty. Let's assume that allEqual is supposed to return True on an empty list. In that case, we can write it like this: allEqual :: [Int] - Bool allEqual (x1:x2:xs) = ??? allEqual _ = ??? where the two ???s are left as an exercise for the reader. -Steve ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Producing MinimumValue
On 19/07/07, Steve Schafer [EMAIL PROTECTED] wrote: On Thu, 19 Jul 2007 10:55:19 -0700 (PDT), you wrote: The question suggests to use some functions defined in the section, and one of them is iSort. Aha. Well, that one certainly lends itself better to this particular proplen than either map or filter. minimumValue :: [Int] - Int minimumValue ns = head (iSort ns) If I were going to use a sort, then yes, that's the way I would do it. Of course, sorting isn't the best way to solve the problem, as sorting will always be at least O(n * log n), whereas a more straightforward algorithm would be O(n). Actually, since Haskell is lazy and only the first element is required for minimumValue, the above algorithm should be O(n). -- Sebastian Sylvan +44(0)7857-300802 UIN: 44640862 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Producing MinimumValue
On Thu, 19 Jul 2007 19:26:39 +0100, you wrote: Actually, since Haskell is lazy and only the first element is required for minimumValue, the above algorithm should be O(n). You're right (as long as the sort algorithm itself is sufficiently lazy, of course). Steve Schafer Fenestra Technologies Corp. http://www.fenestra.com/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Producing MinimumValue
I have defined the first line it seems right to me but second line not sure. I have True or False and whatever value i give it produces that value. allEqual :: [Int] - Bool allEqual (x1:x2:xs) = (x1 == x2) allEqual xs allEqual _ = ??? Steve Schafer wrote: On Thu, 19 Jul 2007 10:55:19 -0700 (PDT), you wrote: The question suggests to use some functions defined in the section, and one of them is iSort. Aha. Well, that one certainly lends itself better to this particular proplen than either map or filter. minimumValue :: [Int] - Int minimumValue ns = head (iSort ns) If I were going to use a sort, then yes, that's the way I would do it. Of course, sorting isn't the best way to solve the problem, as sorting will always be at least O(n * log n), whereas a more straightforward algorithm would be O(n). The other question is to test whether the values of allEqual on inputs 0 to n are all equal. Again, I defined the method but not sure if its concise? allEqual :: [Int] - Bool allEqual xs = length xs == length (filter isEqual xs) where isEqual n = (head xs) == n Simple recursion is probably the most conceptually straightforward approach here. One little difficulty with this problem (and with minimumValue, too) is that the problem isn't completely specified, because we don't know what answer we're supposed to give when the list is empty. Let's assume that allEqual is supposed to return True on an empty list. In that case, we can write it like this: allEqual :: [Int] - Bool allEqual (x1:x2:xs) = ??? allEqual _ = ??? where the two ???s are left as an exercise for the reader. -Steve ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- View this message in context: http://www.nabble.com/Producing-MinimumValue-tf4106379.html#a11696192 Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Producing MinimumValue
On Thursday 19 July 2007, Alexteslin wrote: I have defined the first line it seems right to me but second line not sure. I have True or False and whatever value i give it produces that value. allEqual :: [Int] - Bool allEqual (x1:x2:xs) = (x1 == x2) allEqual xs allEqual _ = ??? Try defining just allEqual [x1, x2, x3] and then generalize that. Jonathan Cast http://sourceforge.net/projects/fid-core http://sourceforge.net/projects/fid-emacs ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Producing MinimumValue
The standard (and simplest) definition for universally quantified predicates (all) starts with True and looks for a False occurrance: Prelude all even [] True Conversely, existentially-quantified predicates (any) start with False and looks for a True occurrance: Prelude any even [] False I would define: allEqual [] = True allEqual [_]= True allEqual (x1:x2:xs) = (x1 == x2) allEqual xs As a purely stylistic note, (per a previous mail thread) you don't need to worry about the order that mutually-exclusive patterns are listed, so I find it clearer to put the base case of an induction first, so I don't forget it. Dan Alexteslin wrote: I have defined the first line it seems right to me but second line not sure. I have True or False and whatever value i give it produces that value. allEqual :: [Int] - Bool allEqual (x1:x2:xs) = (x1 == x2) allEqual xs allEqual _ = ??? Steve Schafer wrote: On Thu, 19 Jul 2007 10:55:19 -0700 (PDT), you wrote: The question suggests to use some functions defined in the section, and one of them is iSort. Aha. Well, that one certainly lends itself better to this particular proplen than either map or filter. minimumValue :: [Int] - Int minimumValue ns = head (iSort ns) If I were going to use a sort, then yes, that's the way I would do it. Of course, sorting isn't the best way to solve the problem, as sorting will always be at least O(n * log n), whereas a more straightforward algorithm would be O(n). The other question is to test whether the values of allEqual on inputs 0 to n are all equal. Again, I defined the method but not sure if its concise? allEqual :: [Int] - Bool allEqual xs = length xs == length (filter isEqual xs) where isEqual n = (head xs) == n Simple recursion is probably the most conceptually straightforward approach here. One little difficulty with this problem (and with minimumValue, too) is that the problem isn't completely specified, because we don't know what answer we're supposed to give when the list is empty. Let's assume that allEqual is supposed to return True on an empty list. In that case, we can write it like this: allEqual :: [Int] - Bool allEqual (x1:x2:xs) = ??? allEqual _ = ??? where the two ???s are left as an exercise for the reader. -Steve ___ 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] Producing MinimumValue
On 7/19/07, Dan Weston [EMAIL PROTECTED] wrote: I would define: allEqual [] = True allEqual [_]= True allEqual (x1:x2:xs) = (x1 == x2) allEqual xs What does this function do for allEqual [1, 1, 2] ? Antoine ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Producing MinimumValue
On Thu, 19 Jul 2007 12:30:06 -0700 (PDT), you wrote: I have defined the first line it seems right to me Close, but not quite. Think of the result that line would give on [1,1,2]. Steve Schafer Fenestra Technologies Corp. http://www.fenestra.com/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Producing MinimumValue
Oops, you got me. I didn't even look at the third line, I just took it from the previous post. My first instinct actually was to write: allEqual x@(h:t) = and (zipWith (==) x t) but I don't think that zipWith is allowed in the question. Dan Antoine Latter wrote: On 7/19/07, Dan Weston [EMAIL PROTECTED] wrote: I would define: allEqual [] = True allEqual [_]= True allEqual (x1:x2:xs) = (x1 == x2) allEqual xs What does this function do for allEqual [1, 1, 2] ? Antoine ___ 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] Producing MinimumValue
Thanks you, that works fine. Sometimes I am not sure what the exercise asks. For example in the section of higher order functions i presume most exercises would be to use those functions, but it seems that that not always true. Dan Weston wrote: The standard (and simplest) definition for universally quantified predicates (all) starts with True and looks for a False occurrance: Prelude all even [] True Conversely, existentially-quantified predicates (any) start with False and looks for a True occurrance: Prelude any even [] False I would define: allEqual [] = True allEqual [_]= True allEqual (x1:x2:xs) = (x1 == x2) allEqual xs As a purely stylistic note, (per a previous mail thread) you don't need to worry about the order that mutually-exclusive patterns are listed, so I find it clearer to put the base case of an induction first, so I don't forget it. Dan Alexteslin wrote: I have defined the first line it seems right to me but second line not sure. I have True or False and whatever value i give it produces that value. allEqual :: [Int] - Bool allEqual (x1:x2:xs) = (x1 == x2) allEqual xs allEqual _ = ??? Steve Schafer wrote: On Thu, 19 Jul 2007 10:55:19 -0700 (PDT), you wrote: The question suggests to use some functions defined in the section, and one of them is iSort. Aha. Well, that one certainly lends itself better to this particular proplen than either map or filter. minimumValue :: [Int] - Int minimumValue ns = head (iSort ns) If I were going to use a sort, then yes, that's the way I would do it. Of course, sorting isn't the best way to solve the problem, as sorting will always be at least O(n * log n), whereas a more straightforward algorithm would be O(n). The other question is to test whether the values of allEqual on inputs 0 to n are all equal. Again, I defined the method but not sure if its concise? allEqual :: [Int] - Bool allEqual xs = length xs == length (filter isEqual xs) where isEqual n = (head xs) == n Simple recursion is probably the most conceptually straightforward approach here. One little difficulty with this problem (and with minimumValue, too) is that the problem isn't completely specified, because we don't know what answer we're supposed to give when the list is empty. Let's assume that allEqual is supposed to return True on an empty list. In that case, we can write it like this: allEqual :: [Int] - Bool allEqual (x1:x2:xs) = ??? allEqual _ = ??? where the two ???s are left as an exercise for the reader. -Steve ___ 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 -- View this message in context: http://www.nabble.com/Producing-MinimumValue-tf4106379.html#a11696723 Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Producing MinimumValue
On 7/19/07, Dan Weston [EMAIL PROTECTED] wrote: Oops, you got me. I didn't even look at the third line, I just took it from the previous post. My first instinct actually was to write: allEqual x@(h:t) = and (zipWith (==) x t) I prefer, allEqual [] = True allEqual xs = foldl1 (==) xs But, unfortunately, it's not a one liner like yours (unless you allow allEqual [] = undefined). Jason but I don't think that zipWith is allowed in the question. Dan Antoine Latter wrote: On 7/19/07, Dan Weston [EMAIL PROTECTED] wrote: I would define: allEqual [] = True allEqual [_]= True allEqual (x1:x2:xs) = (x1 == x2) allEqual xs What does this function do for allEqual [1, 1, 2] ? Antoine ___ 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 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Producing MinimumValue
On 7/19/07, Jason Dagit [EMAIL PROTECTED] wrote: On 7/19/07, Dan Weston [EMAIL PROTECTED] wrote: Oops, you got me. I didn't even look at the third line, I just took it from the previous post. My first instinct actually was to write: allEqual x@(h:t) = and (zipWith (==) x t) I prefer, allEqual [] = True allEqual xs = foldl1 (==) xs But, unfortunately, it's not a one liner like yours (unless you allow allEqual [] = undefined). Oh and silly me, that only works for [Bool]. I'll hushup :) Jason but I don't think that zipWith is allowed in the question. Dan Antoine Latter wrote: On 7/19/07, Dan Weston [EMAIL PROTECTED] wrote: I would define: allEqual [] = True allEqual [_]= True allEqual (x1:x2:xs) = (x1 == x2) allEqual xs What does this function do for allEqual [1, 1, 2] ? Antoine ___ 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 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Producing MinimumValue
The real lesson here is that 1) no problem is too easy to cheat good software engineering practices. 2) no solution not accompanied by at least a QuickCheck result should be viewed with suspicion I obviously have to go back and relearn these lessons. Dan Jason Dagit wrote: On 7/19/07, Jason Dagit [EMAIL PROTECTED] wrote: On 7/19/07, Dan Weston [EMAIL PROTECTED] wrote: Oops, you got me. I didn't even look at the third line, I just took it from the previous post. My first instinct actually was to write: allEqual x@(h:t) = and (zipWith (==) x t) I prefer, allEqual [] = True allEqual xs = foldl1 (==) xs But, unfortunately, it's not a one liner like yours (unless you allow allEqual [] = undefined). Oh and silly me, that only works for [Bool]. I'll hushup :) Jason but I don't think that zipWith is allowed in the question. Dan Antoine Latter wrote: On 7/19/07, Dan Weston [EMAIL PROTECTED] wrote: I would define: allEqual [] = True allEqual [_]= True allEqual (x1:x2:xs) = (x1 == x2) allEqual xs What does this function do for allEqual [1, 1, 2] ? Antoine ___ 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 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Producing MinimumValue
What wrong with my original solution? allEqual2 :: [Int] - Bool allEqual2 xs = length xs == length (filter isEqual xs) where isEqual n = (head xs) == n It looks simpler to me Dan Weston wrote: The real lesson here is that 1) no problem is too easy to cheat good software engineering practices. 2) no solution not accompanied by at least a QuickCheck result should be viewed with suspicion I obviously have to go back and relearn these lessons. Dan Jason Dagit wrote: On 7/19/07, Jason Dagit [EMAIL PROTECTED] wrote: On 7/19/07, Dan Weston [EMAIL PROTECTED] wrote: Oops, you got me. I didn't even look at the third line, I just took it from the previous post. My first instinct actually was to write: allEqual x@(h:t) = and (zipWith (==) x t) I prefer, allEqual [] = True allEqual xs = foldl1 (==) xs But, unfortunately, it's not a one liner like yours (unless you allow allEqual [] = undefined). Oh and silly me, that only works for [Bool]. I'll hushup :) Jason but I don't think that zipWith is allowed in the question. Dan Antoine Latter wrote: On 7/19/07, Dan Weston [EMAIL PROTECTED] wrote: I would define: allEqual [] = True allEqual [_]= True allEqual (x1:x2:xs) = (x1 == x2) allEqual xs What does this function do for allEqual [1, 1, 2] ? Antoine ___ 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 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- View this message in context: http://www.nabble.com/Producing-MinimumValue-tf4106379.html#a11697071 Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Producing MinimumValue
The length command is too greedy. It wants to check the entire length of both lists, and only then compare. If you did this by hand, you would know to quit at the first nonequal element. To do this in Haskell, you should generally avoid length. Lazier functions such as and stop as soon as they can: and (map isEqual xs) doesn't really map to every xs. The and keeps asking map to check the next element for equality, but stops asking when it gets a negative answer. length doesn't know to stop asking. Dan Alexteslin wrote: What wrong with my original solution? allEqual2 :: [Int] - Bool allEqual2 xs = length xs == length (filter isEqual xs) where isEqual n = (head xs) == n It looks simpler to me Dan Weston wrote: The real lesson here is that 1) no problem is too easy to cheat good software engineering practices. 2) no solution not accompanied by at least a QuickCheck result should be viewed with suspicion I obviously have to go back and relearn these lessons. Dan Jason Dagit wrote: On 7/19/07, Jason Dagit [EMAIL PROTECTED] wrote: On 7/19/07, Dan Weston [EMAIL PROTECTED] wrote: Oops, you got me. I didn't even look at the third line, I just took it from the previous post. My first instinct actually was to write: allEqual x@(h:t) = and (zipWith (==) x t) I prefer, allEqual [] = True allEqual xs = foldl1 (==) xs But, unfortunately, it's not a one liner like yours (unless you allow allEqual [] = undefined). Oh and silly me, that only works for [Bool]. I'll hushup :) Jason but I don't think that zipWith is allowed in the question. Dan Antoine Latter wrote: On 7/19/07, Dan Weston [EMAIL PROTECTED] wrote: I would define: allEqual [] = True allEqual [_]= True allEqual (x1:x2:xs) = (x1 == x2) allEqual xs What does this function do for allEqual [1, 1, 2] ? Antoine ___ 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 ___ 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] Producing MinimumValue
On 7/19/07, Alexteslin [EMAIL PROTECTED] wrote: What wrong with my original solution? allEqual2 :: [Int] - Bool allEqual2 xs = length xs == length (filter isEqual xs) where isEqual n = (head xs) == n It looks simpler to me I believe it's correct, but the use of length and filter seems forced. For example, for a very long list that has the second element mismatch, the versions with explicit recursion (or fold variants) will terminate with False as soon as a mismatch is found; the length version will not terminate until both have been fully traversed. If you're allowed to use everything, perhaps the clearest would be: allEqual3 [] = True allEqual3 (x:xs) = all (== x) xs (with all built on top of a fold.) Colin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Producing MinimumValue
On 7/19/07, Sebastian Sylvan [EMAIL PROTECTED] wrote: Actually, since Haskell is lazy and only the first element is required for minimumValue, the above algorithm should be O(n). That's pretty cool :-) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Producing MinimumValue
Hello, I am trying to define a function as part of the exercises that gives a result of a minimum value of the input list of ints. Such as this: minimumValue :: [Int] - Int minimumValue ns ... using either filter or map functions but Not foldr1, because the exercise precedes the section on foldr1. I am confused because using filter - it generates a list on some constraint function for each element. Any hints will be very appreciated. Thank you -- View this message in context: http://www.nabble.com/Producing-MinimumValue-tf4106379.html#a11677240 Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Producing MinimumValue
On 18/07/07, Alexteslin [EMAIL PROTECTED] wrote: Hello, I am trying to define a function as part of the exercises that gives a result of a minimum value of the input list of ints. Such as this: minimumValue :: [Int] - Int minimumValue ns ... using either filter or map functions but Not foldr1, because the exercise precedes the section on foldr1. I am confused because using filter - it generates a list on some constraint function for each element. Any hints will be very appreciated. Thank you Are you allowed to use primitive recursion? minimumValue [x] = x minimumValue (x:xs) = ... -- exercise! -- Sebastian Sylvan +44(0)7857-300802 UIN: 44640862 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Producing MinimumValue
Hi, Am Mittwoch, den 18.07.2007, 13:42 -0700 schrieb Alexteslin: I am trying to define a function as part of the exercises that gives a result of a minimum value of the input list of ints. Such as this: minimumValue :: [Int] - Int minimumValue ns ... using either filter or map functions but Not foldr1, because the exercise precedes the section on foldr1. I am confused because using filter - it generates a list on some constraint function for each element. Any hints will be very appreciated. Thank you Are you allowed to define the function without any of filter or map, just yourself? minimumValue [a] = ... minimumValue (x:xs) = .. x .. minimumValue xs .. Greetings, Joachim -- Joachim Breitner e-Mail: [EMAIL PROTECTED] Homepage: http://www.joachim-breitner.de ICQ#: 74513189 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
