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: [marcin@ah-m2b2 ~]$ 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 <interactive>:1:0: Ambiguous type variable `a' in the constraints: `Fractional a' arising from use of `pnorep' at <interactive>:1:0-5 `Integral a' arising from use of `pnorep' at <interactive>: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!
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:
[marcin@ah-m2b2 ~]$ 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
<interactive>:1:0: Ambiguous type variable `a' in the constraints: `Fractional a' arising from use of `pnorep' at <interactive>:1:0-5 `Integral a' arising from use of `pnorep' at <interactive>: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
participants (2)
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Marcin Tustin -
robert dockins