Thank you all you , that is really impressive . I will read your response carefully , and I think this it is enough to understand it. On 25 May 2010 23:43, Daniel Fischer wrote:

On Tuesday 25 May 2010 23:47:30, Mujtaba Boori wrote:

...

Hello I am try to solve this equation

Define a higher order function that tests whether two functions , both defined on integers , coincide for all integers between 1 and 100

how can I solve this ? is there any thing in Haskell library to solve this kind ?

Sure. Lots of things to do it in different ways. All boil down to - for each integer from 1 to 100 - check whether f i == g i

Look at

http://www.haskell.org/ghc/docs/6.12.2/html/libraries/base-4.2.0.1/Prelude.h... , there are useful functions for this. You will probably want to use 'and' or 'all'.

-- Mujtaba Ali Alboori

On Wednesday 26 May 2010 5:38:57 pm Pete Chown wrote:

test :: (Eq a) => (Int -> a) -> (Int -> a) -> Bool test f1 f2 = unsafePerformIO $ do goodSoFar <- newIORef True forLoop 1 100 $ \i -> when (f1 i /= f2 i) $ writeIORef goodSoFar False readIORef goodSoFar

The problem with this algorithm is that it needlessly tests f1 against f2 for all i, even when a non-matching value has has already been found. Using the power of call-with-current-continuation, I have constructed an algorithm that lacks this deficiency: import Control.Monad.Cont test f g = flip runCont id . callCC $ \escape -> do forM_ [1..100] $ \n -> when (f n /= g n) $ escape False return True This should perform almost 75% less work in the testFunc1 case! It certainly feels much snappier. -- Dan

Mujtaba Boori wrote:

I think this answer agree100 f g = map f xs == map g xs where xs = [1..100] from  Richard O'Keefe is do the job.

agree100 = (==) `on` for [1..100] Regards, Yitz

On 28 May 2010 09:37, Richard O'Keefe wrote:

On May 27, 2010, at 11:50 PM, Yitzchak Gale wrote:

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agree100 = (==) `on` for [1..100]

Search for "on" and "for" in the Haskell 98 Report and you will not find them.  If you want to tell someone to use them, you ought to tell them where to find them.

You mean like this? http://haskell.org/hoogle/?hoogle=on http://haskell.org/hoogle/?hoogle=for -- Ivan Lazar Miljenovic Ivan.Miljenovic@gmail.com IvanMiljenovic.wordpress.com

On 28 May 2010 14:52, Richard O'Keefe wrote:> Yes, that kind of thing.

Remember, this was a BEGINNER-type question. If one is giving a *serious* answer, it has to be an answer a beginner (who has almost certainly never heard of Traversable) can make sense of, and if it uses functions that are pretty much certain not to be in said beginner's text book, said beginner has to be told quite clearly where to find them.

I think this is an example of the "Haskell effect" (more typically seen on #haskell), which can be categorised as follows: 1) Someone asks a (usually rather simple) question. 2) People discuss this and provide several straightforward and relevant answers. 3) Out of curiosity (and probably a fair dose of masochism) others then start to golf the solution into the most interesting approach possible. 4) The person that asked the question initially gets lost (but is quite often awed at all the amazing stuff that's going on around them zooming past at light speed). 5) People suddenly remember that there was an initial question and make an attempt to explain the more advanced solutions to the person that asked the question in the first place. 6) They smile and nod and pretend they understand whilst putting a note onto their copious TODO list to someday sit down and try to work out wtf was going on. 7) ??? 8) Profit!!! -- Ivan Lazar Miljenovic Ivan.Miljenovic@gmail.com IvanMiljenovic.wordpress.com

Richard O'Keefe wrote:

If one is giving a *serious* answer, it has to be an answer a beginner (who has almost certainly never heard of Traversable) can make sense of, and if it uses functions that are pretty much certain not to be in said beginner's text book, said beginner has to be told quite clearly where to find them.

You're right. It wasn't really a serious answer, it was meant for fun. Definitely along the lines of Ivan's "Haskell Effect". I think Mujtaba has been enjoying this discussion. I hope we'll be seeing more of him around here. Thanks to you and Ivan for pointing out sources, though. My "for" function was indeed "flip map". Perhaps it's not in any library, but it's often seen on the #haskell IRC channel. :) Regards, Yitz

* sure I did enjoy the discussion here Yitzchak Gale. I have already submitted several questions ,and you guys were very helpful. However , I am not sure how I will use Haskell other than my Haskell course that has just finished. * On 28 May 2010 14:52, Ivan Lazar Miljenovic wrote:

Yitzchak Gale writes:

...

My "for" function was indeed "flip map". Perhaps it's not in any library, but it's often seen on the #haskell IRC channel. :)

Hmmm, I had never heard of this but going back through my logs I do indeed find nornagon, jethr0 and jmcarthur all either stating this definition or advocating it. Alternate definitions that I found include:

* pam (ski)

* -<< (vixey)

-- Ivan Lazar Miljenovic Ivan.Miljenovic@gmail.com IvanMiljenovic.wordpress.com

-- Mujtaba Ali Alboori

On Thursday 27 May 2010 9:05:40 pm Ivan Miljenovic wrote:

On 28 May 2010 09:37, Richard O'Keefe wrote:

...

On May 27, 2010, at 11:50 PM, Yitzchak Gale wrote:

...

agree100 = (==) `on` for [1..100]

Search for "on" and "for" in the Haskell 98 Report and you will not find them. If you want to tell someone to use them, you ought to tell them where to find them.

You mean like this?

http://haskell.org/hoogle/?hoogle=on http://haskell.org/hoogle/?hoogle=for

for from Data.Traversable cannot be what was intended, because it would require the functions to have type: a -> F b for some Applicative F (which, moreover, should be providing the Eq instance you want to check with). This works for the identity functor (assuming the instance is declared), but the code is still not right, since the definition given doesn't lift the functions. Rather: for = flip map presumably. But this definition isn't in any of the standard libraries (at least visibly) to my knowledge. -- Dan