Hi, Newbie question. Given the inferred type for square, the inferred types for quad1, quad2 and quad3 are what I would expect. Is there a straightforward explanation (i.e. one that a newbie would understand) as to why the inferred type for quad4 is less general? Regards, dl -- GHC Interactive, version 6.4, for Haskell 98. Prelude> let square x = x * x Prelude> :t square square :: (Num a) => a -> a Prelude> let quad1 x = square (square x) Prelude> :t quad1 quad1 :: (Num a) => a -> a Prelude> let quad2 x = square $ square x Prelude> :t quad2 quad2 :: (Num a) => a -> a Prelude> let quad3 x = (square . square) x Prelude> :t quad3 quad3 :: (Num a) => a -> a Prelude> let quad4 = square . square Prelude> :t quad4 quad4 :: Integer -> Integer ___________________________________________________________ Yahoo! Photos NEW, now offering a quality print service from just 8p a photo http://uk.photos.yahoo.com _______________________________________________ Haskell-Cafe mailing list [hidden email] http://www.haskell.org/mailman/listinfo/haskell-cafe |
I think this is the monomorphism restriction, you can see more details
on the web page: http://www.haskell.org/hawiki/MonomorphismRestriction On 3/30/06, David Laffin <[hidden email]> wrote: > > Hi, > > Newbie question. Given the inferred type for square, > the > inferred types for quad1, quad2 and quad3 are what I > would > expect. Is there a straightforward explanation (i.e. > one > that a newbie would understand) as to why the inferred > type > for quad4 is less general? > > Regards, > dl > > -- GHC Interactive, version 6.4, for Haskell 98. > > Prelude> let square x = x * x > Prelude> :t square > square :: (Num a) => a -> a > > Prelude> let quad1 x = square (square x) > Prelude> :t quad1 > quad1 :: (Num a) => a -> a > > Prelude> let quad2 x = square $ square x > Prelude> :t quad2 > quad2 :: (Num a) => a -> a > > Prelude> let quad3 x = (square . square) x > Prelude> :t quad3 > quad3 :: (Num a) => a -> a > > Prelude> let quad4 = square . square > Prelude> :t quad4 > quad4 :: Integer -> Integer > > > > > > > ___________________________________________________________ > Yahoo! Photos – NEW, now offering a quality print service from just 8p a photo http://uk.photos.yahoo.com > _______________________________________________ > Haskell-Cafe mailing list > [hidden email] > http://www.haskell.org/mailman/listinfo/haskell-cafe > Haskell-Cafe mailing list [hidden email] http://www.haskell.org/mailman/listinfo/haskell-cafe |
most probably yes. I had the exact same question for:
module Factors where import Prelude divides x y = (mod x y == 0) factors x = filter (divides x) [1..x] nonTrivialFactors x = filter (\y -> y /= 1 && y /= x) [1..x] isEmpty [] = True isEmpty _ = False -- isPrime = isEmpty . nonTrivialFactor -- says isPrime :: Integer -> Bool -- this one say isPrime :: (Integral a) => a -> Bool isPrime x = isEmpty (nonTrivialFactors x) frankly this is not desired, but I cannot see why it's particularly harmful. is it? note: I was devising this example mostly to show the usefulness of laziness ;) --- Neil Mitchell <[hidden email]> wrote: > I think this is the monomorphism restriction, you > can see more details > on the web page: > > http://www.haskell.org/hawiki/MonomorphismRestriction > > On 3/30/06, David Laffin <[hidden email]> > wrote: > > > > Hi, > > > > Newbie question. Given the inferred type for > square, > > the > > inferred types for quad1, quad2 and quad3 are what > I > > would > > expect. Is there a straightforward explanation > (i.e. > > one > > that a newbie would understand) as to why the > inferred > > type > > for quad4 is less general? > > > > Regards, > > dl > > > > -- GHC Interactive, version 6.4, for Haskell 98. > > > > Prelude> let square x = x * x > > Prelude> :t square > > square :: (Num a) => a -> a > > > > Prelude> let quad1 x = square (square x) > > Prelude> :t quad1 > > quad1 :: (Num a) => a -> a > > > > Prelude> let quad2 x = square $ square x > > Prelude> :t quad2 > > quad2 :: (Num a) => a -> a > > > > Prelude> let quad3 x = (square . square) x > > Prelude> :t quad3 > > quad3 :: (Num a) => a -> a > > > > Prelude> let quad4 = square . square > > Prelude> :t quad4 > > quad4 :: Integer -> Integer > > > > > > > > > > > > > > > > > Yahoo! Photos ï¿½ NEW, now offering a quality > service from just 8p a photo > http://uk.photos.yahoo.com > > _______________________________________________ > > Haskell-Cafe mailing list > > [hidden email] > > > http://www.haskell.org/mailman/listinfo/haskell-cafe > > > _______________________________________________ > Haskell-Cafe mailing list > [hidden email] > http://www.haskell.org/mailman/listinfo/haskell-cafe > __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com _______________________________________________ Haskell-Cafe mailing list [hidden email] http://www.haskell.org/mailman/listinfo/haskell-cafe |
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