Re: [Haskell-cafe] Typing problems with basic arithmetic - help!
On Sat, 24 Sep 2005, Marcin Tustin wrote: > For some reason the following code is producing an error message from ghci > that the the patterns are non-exhaustive. Does anyone have any idea why that > could be, given that the patterns are, at least in my meaning, provably > exhaustive? > > choosenonuniqueset n (a:r) > | (length r) > (n-1) = [ (sort (a:x)) | x <- (choosenonuniqueset (n-1) > r)] > `union` > [ (sort (a:x)) | x <- (choosenonuniqueset n r)] > | (length r) == (n-1) = [a:r] > | (length r) < (n-1) = [] You need to compare only once. Better write: choosenonuniqueset n (a:r) = case compare (length r) (n-1) of GT -> ... EQ -> [a:r] LT -> [] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Typing problems with basic arithmetic - help!
On Fri, 23 Sep 2005, Marcin Tustin wrote: > Thanks for this: All I have to do now is fix the fact that my maths is > stupidly screwed! 'div' is the integer division and rounds down. You should either use Rational (or Double) everywhere or use % which builds a ratio from two integers. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Typing problems with basic arithmetic - help!
Well...your recursion will fail if (a:r) is matched against the empty set. That will trigger your Exception. So does your code avoid this ? No, it does not. cus 2 [1,2,3,4,5] recurses to cus 1 [2,3,4,5] to cus 0 [3,4,5] to cus (-1) [4,5] to cus (-2) [5] to cus (-3) [] ---Exception You need a n<=0 guard case AND an empty list base case chooseuniqueset _ [] = [] choosenonuniqueset n (a:r) | n<=0 = [] -- This needs to be the first guard Also, you're sorting is poor. The first case sorts too much and the second case does no sorting. Marcin Tustin wrote: > For some reason the following code is producing an error message from ghci > that the the patterns are non-exhaustive. Does anyone have any idea why that > could be, given that the patterns are, at least in my meaning, provably > exhaustive? > > choosenonuniqueset n (a:r) > | (length r) > (n-1) = [ (sort (a:x)) | x <- (choosenonuniqueset (n-1) > r)] > `union` > [ (sort (a:x)) | x <- (choosenonuniqueset n r)] > | (length r) == (n-1) = [a:r] > | (length r) < (n-1) = [] > > Error message is: > > *Main> :reload > Compiling Main ( birthday.hs, interpreted ) > Ok, modules loaded: Main. > *Main> choosenonuniqueset 2 [1..5] > *** Exception: birthday.hs:(22,0)-(27,29): Non-exhaustive patterns in > function choosenonuniqueset > > *Main> choosenonuniqueset 5 [1..5] > [[1,2,3,4,5]] > *Main> > ___ > 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] Typing problems with basic arithmetic - help!
For some reason the following code is producing an error message from ghci that the the patterns are non-exhaustive. Does anyone have any idea why that could be, given that the patterns are, at least in my meaning, provably exhaustive? choosenonuniqueset n (a:r) | (length r) > (n-1) = [ (sort (a:x)) | x <- (choosenonuniqueset (n-1) r)] `union` [ (sort (a:x)) | x <- (choosenonuniqueset n r)] | (length r) == (n-1) = [a:r] | (length r) < (n-1) = [] Error message is: *Main> :reload Compiling Main ( birthday.hs, interpreted ) Ok, modules loaded: Main. *Main> choosenonuniqueset 2 [1..5] *** Exception: birthday.hs:(22,0)-(27,29): Non-exhaustive patterns in function choosenonuniqueset *Main> choosenonuniqueset 5 [1..5] [[1,2,3,4,5]] *Main> ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Typing problems with basic arithmetic - help!
Thanks for this: All I have to do now is fix the fact that my maths is stupidly screwed! On Fri, Sep 23, 2005 at 02:23:10PM -0400, J. Garrett Morris wrote: > Haskell doesn't do automatic numeric conversion for you - you need to > use fromIntegral to go from an integral type (like 2) to a floating > point type (as you'd need for division) and you can use round or trunc > to go the other direction. There's similarly a fromRational function > to convert from rational numbers to just about anything else you'd > need. A couple of applications of those functions - probably mainly > around your divisions - should fix things up. > > /g ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Typing problems with basic arithmetic - help!
For the version with type signatures, you are trying to divide integers using the (/) function. This function expects values in the class Fractional, and Integer isn't a member. Replace with div, which does integer division. pnorep days n = (numeratorex days n) `div` (denominatorex days n) Marcin Tustin wrote: I'm trying to do some basic arithmetic code (in fact it calculates the probability of a birthday clash given year length and group size), and GHC and Hugs are both not liking the code: [EMAIL PROTECTED] ~]$ ghci burthday.hs ___ ___ _ / _ \ /\ /\/ __(_) / /_\// /_/ / / | | GHC Interactive, version 6.4, for Haskell 98. / /_\\/ __ / /___| | http://www.haskell.org/ghc/ \/\/ /_/\/|_| Type :? for help. Loading package base-1.0 ... linking ... done. Compiling Main ( burthday.hs, interpreted ) burthday.hs:14:37: No instance for (Fractional Integer) arising from use of `/' at burthday.hs:14:37 Probable fix: add an instance declaration for (Fractional Integer) In the definition of `pnorep': pnorep days n = (numeratorex days n) / (denominatorex days n) Failed, modules loaded: none. Prelude> :reload Compiling Main ( burthday.hs, interpreted ) Ok, modules loaded: Main. *Main> pnorep 365 30 :1:0: Ambiguous type variable `a' in the constraints: `Fractional a' arising from use of `pnorep' at :1:0-5 `Integral a' arising from use of `pnorep' at :1:0-5 Probable fix: add a type signature that fixes these type variable(s) *Main> The first time is with the type annotations, the second without: import Ratio import Numeric numeratorex days n = (numdays days n) - (subtractex days n) -- :: Rational numdays days n = days * n --numdays :: Integer -> Integer -> Integer subtractex days n = (days * (days - 1)) / 2 --:: Rational denominatorex days n = (days^n) -- denominatorex :: Integer -> Integer -> Integer pnorep days n = (numeratorex days n) / (denominatorex days n) Help! Thanks! ___ 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] Typing problems with basic arithmetic - help!
I'm trying to do some basic arithmetic code (in fact it calculates the probability of a birthday clash given year length and group size), and GHC and Hugs are both not liking the code: [EMAIL PROTECTED] ~]$ ghci burthday.hs ___ ___ _ / _ \ /\ /\/ __(_) / /_\// /_/ / / | | GHC Interactive, version 6.4, for Haskell 98. / /_\\/ __ / /___| | http://www.haskell.org/ghc/ \/\/ /_/\/|_| Type :? for help. Loading package base-1.0 ... linking ... done. Compiling Main ( burthday.hs, interpreted ) burthday.hs:14:37: No instance for (Fractional Integer) arising from use of `/' at burthday.hs:14:37 Probable fix: add an instance declaration for (Fractional Integer) In the definition of `pnorep': pnorep days n = (numeratorex days n) / (denominatorex days n) Failed, modules loaded: none. Prelude> :reload Compiling Main ( burthday.hs, interpreted ) Ok, modules loaded: Main. *Main> pnorep 365 30 :1:0: Ambiguous type variable `a' in the constraints: `Fractional a' arising from use of `pnorep' at :1:0-5 `Integral a' arising from use of `pnorep' at :1:0-5 Probable fix: add a type signature that fixes these type variable(s) *Main> The first time is with the type annotations, the second without: import Ratio import Numeric numeratorex days n = (numdays days n) - (subtractex days n) -- :: Rational numdays days n = days * n --numdays :: Integer -> Integer -> Integer subtractex days n = (days * (days - 1)) / 2 --:: Rational denominatorex days n = (days^n) -- denominatorex :: Integer -> Integer -> Integer pnorep days n = (numeratorex days n) / (denominatorex days n) Help! Thanks! ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
