Re: [Haskell-cafe] Infinite loop?
On Fri, 17 Feb 2006 17:26:08 + Jon Fairbairn [EMAIL PROTECTED] wrote: On 2006-02-17 at 09:22PST Jared Updike wrote: Yep. change one line to: entry - if isdir name /= . name /= .. and it does in fact work. Only if no-one has been tricky with symbolic links. And how can you, in Haskell, detect symbolic links ? -- You have an unusual understanding of the problems of human relationships. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: libreadline dependency
J. Scott Thayer, M.D. wrote: Haskell wants libreadline 4 while I have libreadline 5. I'm not sure about SUSE, but Fedora has libreadline_compat packages. HTH, Jim ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] classes inheritance seems not to work.
On 2/18/06, asker [EMAIL PROTECTED] wrote: Hi, I'm trying to make three haskell classes and an instance this way: -- class (Eq a) = Graph a where vert :: [a] ady :: a - [a] class (Graph a) = Paths a where gps :: a - a - [[a]] class (Paths a) = Minimum a where mgps :: a - a - [a] instance Minimum Char where vert = ['a' .. 'f'] -- This is the line of the error message. ady 'a' = ['b', 'c'] ady 'b' = ['d', 'c', 'e'] ady 'd' = ['f'] gps = bepgr -- bepgr is defined and implemented in other code's part mgps = head gps -- When I try to run this I get: ERROR: filepath:line -No member vert in class Minimum I don't know why does this happen, am I doing something wrong? The class Minimum doesn't have a member 'vert', Graph does, though. You need to instantiate your data type in all three classes separately. So three separate instance declarations, one for each class. -- Sebastian Sylvan +46(0)736-818655 UIN: 44640862 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Infinite loop?
Quoth Barbier de Reuille Pierre [EMAIL PROTECTED]: | On Fri, 17 Feb 2006 17:26:08 + | Jon Fairbairn [EMAIL PROTECTED] wrote: | | On 2006-02-17 at 09:22PST Jared Updike wrote: | Yep. change one line to: | | entry - if isdir name /= . name /= .. | | and it does in fact work. | | Only if no-one has been tricky with symbolic links. | | | And how can you, in Haskell, detect symbolic links ? I refer you to the documentation in System.Posix.Files, especially getFileStatus :: FilePath - IO FileStatus, and isSymbolicLink :: FileStatus - Bool. I don't think I've used this function, but it looks promising. Donn Cave, [EMAIL PROTECTED] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Infinite loop?
Barbier de Reuille Pierre wrote: And how can you, in Haskell, detect symbolic links ? One can use System.Posix.Files.isSymbolicLink function for that purpose. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Infinite loop?
Barbier de Reuille Pierre [EMAIL PROTECTED] writes: (snip) And how can you, in Haskell, detect symbolic links ? I use System.Posix.Files. getSymbolicLinkStatus is like lstat(2) under Unix. It returns a value to which you can apply the isSymbolicLink predicate. Of course, you can't be sure the file won't change in between you checking and you acting on that result. -- Mark ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GADTs and bar :: Foo t1 - Foo t2
My thanks for the responses received off-list. Dimitrios pointed out that a 'successor' class solution would require the typechecking to depend somehow on whether the lists were empty or not. Probably a clue that I was on the wrong track. Both Cale and Dimitrios suggested better solutions involving different data types: data FooA = A data FooB = B [FooA] data FooC = C [FooB] data Foo = FA FooA | FB FooB | FC FooC or data Node a = N [a] deriving Show data Tree a = Zero a | Succ (Tree (Node a)) deriving Show or data EXFoo where EXFoo :: Foo a - EXFoo Embarrassingly simple! :) Thanks Daniel On Friday 17 February 2006 19:18, Daniel McAllansmith wrote: Hello, I have a recursive type data Foo = A | B [Foo] | C [Foo] that I would like to restrict so that a C can only contain Bs, and a B can only contain As. If I use a GADT as follows the bar function, understandably, will not type check. data AType data BType data CType data Foo a where A :: Foo AType B :: [Foo AType] - Foo BType C :: [Foo BType] - Foo CType --get the successor of the Foo bar c@(C [] ) = c bar (C (b:_)) = b bar b@(B [] ) = b bar (B (a:_)) = a bar [EMAIL PROTECTED] = a How do I achieve this restriction? Do I need to have some sort of successor class with dependent types? Ta Daniel ___ 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] Shapes Compiling Error
Hi everybody, I have written some code for several shapes, and i get a compiling error: parse error on input `:' though I can't find where the error is... data Shape = Ellipse Radius Radius | Polygon [Vertex] deriving Show type Radius = Float type Vertex = (Float, Float) area :: Shape - Float area (Rectangle s1 s2) = s1 * s2 area (RtTriangle s1 s1) = s1 *s2 /2 area (Ellipse r1 r2) = pi * r1 * r2 area (Polygon(v1:v2:v3:vs)) = triArea v1 v2 v3 + area(Polygon(v1:v3:vs)) area(Polygon _ ) = 0 area (Polygon(v1:vs')) = polyArea vs where polyArea :: [Vertex] - Float polyArea(v2:v3:vs') = triArea v1 v2 v3 + polyArea(v3:vs') polyArea _= 0 triArea :: Vertex - Vertex - Vertex - Float triArea v1 v2 v3 = let a = distBeetween v1 v2 b = distBeetween v2 v3 c = distBeetween v3 v1 s = 0.5 * (a + b + c) in sqrt (s * (s - a) * (s - b) * (s - c)) distBeetween :: Vertex - Vertex - Float distBeetween (x1, y1) (x2, y2) = sqrt ((x1 - x2) ^ 2 + (y1 - y2) ^ 2) Any suggestions? Thanks in advance, Skag55 _ On the road to retirement? Check out MSN Life Events for advice on how to get there! http://lifeevents.msn.com/category.aspx?cid=Retirement ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Shapes Compiling Error
Hi, Am Sonntag, 19. Februar 2006 22:57 schrieb Chatzianastassiou Achilleas: Hi everybody, I have written some code for several shapes, and i get a compiling error: parse error on input `:' though I can't find where the error is... [snip code] ever heard of the layout-rule? You must indent the cases for polyArea to exactly the same level as the type-declaration, and all declarations in the let-binding to the same level. Once the indentation is corrected, you get the real error messages -- those you should understand easily. Cheers, Daniel -- In My Egotistical Opinion, most people's C programs should be indented six feet downward and covered with dirt. -- Blair P. Houghton ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Shapes Compiling Error
Watch how deeply things are indented. The definitions for polyArea should be indented to the same level as its type signature. Currently, they're indented a little more, so the first line of polyArea's definition is being treated as part of the type signature, which is why you're getting the error. GHC/GHCi/hugs should be telling you also what line the error happens on, which should be a good clue here :) - Cale On 19/02/06, Chatzianastassiou Achilleas [EMAIL PROTECTED] wrote: Hi everybody, I have written some code for several shapes, and i get a compiling error: parse error on input `:' though I can't find where the error is... data Shape = Ellipse Radius Radius | Polygon [Vertex] deriving Show type Radius = Float type Vertex = (Float, Float) area :: Shape - Float area (Rectangle s1 s2) = s1 * s2 area (RtTriangle s1 s1) = s1 *s2 /2 area (Ellipse r1 r2) = pi * r1 * r2 area (Polygon(v1:v2:v3:vs)) = triArea v1 v2 v3 + area(Polygon(v1:v3:vs)) area(Polygon _ ) = 0 area (Polygon(v1:vs')) = polyArea vs where polyArea :: [Vertex] - Float polyArea(v2:v3:vs') = triArea v1 v2 v3 + polyArea(v3:vs') polyArea _= 0 triArea :: Vertex - Vertex - Vertex - Float triArea v1 v2 v3 = let a = distBeetween v1 v2 b = distBeetween v2 v3 c = distBeetween v3 v1 s = 0.5 * (a + b + c) in sqrt (s * (s - a) * (s - b) * (s - c)) distBeetween :: Vertex - Vertex - Float distBeetween (x1, y1) (x2, y2) = sqrt ((x1 - x2) ^ 2 + (y1 - y2) ^ 2) Any suggestions? Thanks in advance, Skag55 _ On the road to retirement? Check out MSN Life Events for advice on how to get there! http://lifeevents.msn.com/category.aspx?cid=Retirement ___ 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] Shapes Compiling Error
Thanks everybody, I think it was the layout thing that I misstyped plus the area (RtTriangle s1 s1) = s1 *s2 /2 (silly me!) Skag55 _ Dont just search. Find. Check out the new MSN Search! http://search.msn.click-url.com/go/onm00200636ave/direct/01/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Unexpected results with simple IO
What version of GHC are you using? Your code works for me in rxvt in Cygwin, with GHC 6.4.1. But I remember having that same problem earlier (in some earlier GHC version, so it may be fixed by now). The solution was to run hFlush after each putStr, like so: import System.IO (hFlush, stdout) do putStr ... hHlush stdout ... If I remember correctly, the problem only occurred in GHCi and Hugs -- not when compiling the code. / Emil Maurício skrev: You're right... I was running the example in rxvt, in cygwin. Now I tried in Windows command shell and it works. Thanks, Maurício Cale Gibbard wrote: That doesn't happen for me at all, it works just fine. Maybe it's something wrong with your terminal? You could possibly try playing with the buffering settings on stdout, using hSetBuffering in System.IO. - Cale On 17/02/06, Maurício [EMAIL PROTECTED] wrote: Dear Haskell users, I have a problem using IO. The small test program below asks the user to guess from a list of random numbers between 1 and 10. Everything works well excepts for one problem: all the messages (Guess a number..., Right... and Wrong...) are printed after the program finishes, i.e., I have to use it blind. I'm afraid I misunderstand something important about lazyness or monads... What am I doing wrong? Thanks, Maurício module Main where import Random main = do r_gen - getStdGen --random generator let r_list = (randomRs (1,10) r_gen) --random list guess_loop (r_list) guess_loop (r:r_others) = do putStrLn Guess a number between 1 and 10: n - readLn if n==r then do putStrLn Right! :) return () else do putStrLn Wrong... :( guess_loop r_others ___ 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
