Hi, You probably want to read up on: Monomorphism restriction (I don't think this applies here, but I'm never too sure!): http://www.haskell.org/hawiki/MonomorphismRestriction Defaulting: http://www.haskell.org/onlinereport/decls.html#sect4.3.4 I don't understand either to any great degree, but when points free starts changing things, its usually one of those two kicking in. And as a side note, haskell@ tends to be used more for announcements, and haskell-cafe@ is used more for asking questions etc. Thanks Neil On 11/3/06, Dan Weston wrote:

Help! One of two things is going on:

1) I don't understand what I'm doing 2) GHC is inferring different types for pointed and point-free function definition.

I wanted to define Haskell equivalents to the C ternary operator. Basically, predicate ??? doIfTrue ||| doIfFalse

For some reason, though, in GHC 6.4 and 6.7, the types inferred for abs1 and ab2 (defined below) are different:

*Main> :t abs1 abs1 :: (Num a, Ord a) => a -> a

*Main> :t abs2 abs2 :: Integer -> Integer

How is abs2 less general just because I use point-free notation instead of pointed notation? They should have the same type, no? I'm stumped...

...

import Control.Arrow import Data.Either

infix 1 ?, ??, ???, ????

(?) True = Left (?) False = Right

(??) True = Left . fst (??) False = Right . snd

p ??? q = (p &&& arr id) >>> uncurry (?) >>> q p ???? q = (p &&& arr id) >>> uncurry (??) >>> q

abs1 x = (< 0) ??? negate ||| id $ x abs2 = (< 0) ??? negate ||| id

checks :: [Bool] checks = [ (True ? 3 ) == (Left 3), (False ? 4 ) == (Right 4), (True ?? (3,4)) == (Left 3), (False ?? (3,4)) == (Right 4), (even ??? (`div` 2) ||| (+1).(*3) $ 3 ) == ( 10), (even ??? (`div` 2) ||| (+1).(*3) $ 4 ) == ( 2), (uncurry (==) ???? (+1) ||| (*3) $ (3,3)) == ( 4), (uncurry (==) ???? (+1) ||| (*3) $ (3,4)) == ( 12), (uncurry (==) ???? (+1) +++ (*3) $ (3,3)) == (Left 4), (uncurry (==) ???? (+1) +++ (*3) $ (3,4)) == (Right 12), (abs1 5 ) == ( 5), (abs1 (-5) ) == ( 5), (abs2 5 ) == ( 5), (abs2 (-5) ) == ( 5) ]

main = print (and checks)

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