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Comparison with Clean?
by Daniel Carrera 04 May '05

04 May '05

Hi all, Anyone here familiar with the Clean programming language? http://www.cs.ru.nl/~clean/ It looks /very/ similar to Haskell, both in functionality and syntax. I would be grateful for any sort of comparison. I'm trying to decide which language I should try to learn. Cheers, Daniel.

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Speed comparison?
by Daniel Carrera 04 May '05

04 May '05

Hi all, Thank you for all the information on my previous question. I learned a lot, and good pointers to more info. My next question is about speed. How fast would you consider Haskell? (say, for computational work). How would you compare it to C, Python and Ruby? I suggest C, Python and Ruby as a basis of comparison because: 1) C is what I'd use if I wanted something fast. 2) Python or Ruby is what I'd use if I wanted clean code. I know that Haskell can be compiled, thanks to ghc. Ruby is interpreted and I'm pretty sure Python is quasi-interpreted (it's "compiled" on the fly to Java-style bytecode and a VM runs the bytecode). Furthermore, the Haskell page says that ghc produces fast programs. So I would guess that Haskell is faster than Python, but not as fast as C. Would that be correct? For computational work (e.g. a simulation, factoring primes, whatever) does it approach C speed? I would be happy to hear a comparison with any other language you find interesting.:-) As well as any other information you'd like to share. Cheers, Daniel.

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Re: [Haskell-cafe] Speed comparison?
by John Hughes 04 May '05

04 May '05

>>Furthermore, the Haskell page says that ghc produces fast programs. >>So I would guess that Haskell is faster than Python, but not as fast >>as C. >> >>Would that be correct? >> >> > >Usually yes. > > > In a sense. I think it's important to remember that what matters is performance of a whole application, not of highly tuned benchmark code, and in writing applications with good performance, then the quality of profiling tools, and (especially) the amount of time the programmer has available for tuning, can be far more important than the compiler. There have certainly been occasions where Haskell entries to the ICFP programming contest have beat OCaml or even C/C++ entries on performance, by a wide margin. Likewise Ericsson's ATM switch, which is controlled by a million lines plus of Erlang (running on a byte code interpreter!), performs better than all its competitors. Benchmarks give a very one-sided view, ignoring the large effect that ease of programming can have on the final system's performance. John Hughes

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RE: [Haskell-cafe] Mutual recursive modules with GHC: Classes, instances
by Simon Peyton-Jones 04 May '05

04 May '05

I'm afraid so, as of today. It's the kind of thing that could get fixed if enough people wanted it, but at the moment it's pretty low on the list. Simon | -----Original Message----- | From: haskell-cafe-bounces(a)haskell.org [mailto:haskell-cafe-bounces@haskell.org] On Behalf Of | Henning Thielemann | Sent: 04 May 2005 10:31 | To: Simon Peyton-Jones | Cc: Haskell Cafe | Subject: RE: [Haskell-cafe] Mutual recursive modules with GHC: Classes,instances | | | On Wed, 4 May 2005, Simon Peyton-Jones wrote: | | > hi-boot files can't contain class declarations. This should be checked, | > but isn't, hence puzzling message. | > | > GHC 6.4 has a better setup. Actually, it still doesn't check for | > absence of class decls, but it will shortly. | | This means it is impossible to declare mutually dependent classes where | each class resides in a separate module? | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe

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Comparison with Clean?
by Krasimir Angelov 04 May '05

04 May '05

If you want to compare Haskell and Clean then take a look at Object I/O library. It is ported to Haskell and you can learn a lot comparing both implementations. I spent a lot of time translating Clean functions to Haskell and my own impression is that Haskell's do notation is much more easier that uniqueness typing. In Clean you have to explicitly maintain the state while in Haskell it is hidden. In order to preserve uniquenes property of state, quite often you have write uggly functions like: getXYZ :: State -> (XYZ, State) getXYZ st = (f st, st) while in Haskell the above function should be: getXYZ :: State -> XYZ getXYZ st = f st It is more clean and from the type signature you can see that this is readonly access to the state. Cheers, Krasimir On 5/4/05, Daniel Carrera <dcarrera(a)digitaldistribution.com> wrote: > Hi all, > > Anyone here familiar with the Clean programming language? > > http://www.cs.ru.nl/~clean/ > > It looks /very/ similar to Haskell, both in functionality and syntax. > > I would be grateful for any sort of comparison. I'm trying to decide > which language I should try to learn. > > Cheers, > Daniel. > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

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RE: [Haskell-cafe] Mutual recursive modules with GHC: Classes, instances
by Simon Peyton-Jones 04 May '05

04 May '05

hi-boot files can't contain class declarations. This should be checked, but isn't, hence puzzling message. GHC 6.4 has a better setup. Actually, it still doesn't check for absence of class decls, but it will shortly. Simon | -----Original Message----- | From: haskell-cafe-bounces(a)haskell.org [mailto:haskell-cafe-bounces@haskell.org] On Behalf Of | Henning Thielemann | Sent: 04 May 2005 10:10 | To: Haskell Cafe | Subject: [Haskell-cafe] Mutual recursive modules with GHC: Classes, instances | | | I tried to set up mutual recursive modules according to section 4.6.10. of | the manual of GHC-6.2.2. I illustrate my problems with a simple fictitious | example. | | ---- A.hi-boot ---- | | module A where | | | class GHC.Num.Num a => C a where | answer :: a | | f :: B.T -> GHC.Num.Int | | | ---- A.hs ---- | | module A where | | import B | | class Num a => C a where | answer :: a | | instance C Int where | answer = 42 | | f :: B.T -> Int | f (B.Cons x) = x | | | ---- B.hs ---- | | module B where | | import {-# SOURCE #-} A | | | data T = Cons Int | | newAnswer :: Int | newAnswer = A.answer + 1 | | -------------- | | | $ ghc --make A.hs B.hs | Chasing modules from: A.hs,B.hs | Compiling B ( B.hs, B.o ) | | B.hs:1: | Failed to find interface decl for `A.$dmanswer' | from module `A' | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe

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[Haskell-cafe] Mutual recursive modules with GHC: Classes, instances
by Henning Thielemann 04 May '05

04 May '05

I tried to set up mutual recursive modules according to section 4.6.10. of the manual of GHC-6.2.2. I illustrate my problems with a simple fictitious example. ---- A.hi-boot ---- module A where class GHC.Num.Num a => C a where answer :: a f :: B.T -> GHC.Num.Int ---- A.hs ---- module A where import B class Num a => C a where answer :: a instance C Int where answer = 42 f :: B.T -> Int f (B.Cons x) = x ---- B.hs ---- module B where import {-# SOURCE #-} A data T = Cons Int newAnswer :: Int newAnswer = A.answer + 1 -------------- $ ghc --make A.hs B.hs Chasing modules from: A.hs,B.hs Compiling B ( B.hs, B.o ) B.hs:1: Failed to find interface decl for `A.$dmanswer' from module `A'

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Array functions?
by Daniel Carrera 04 May '05

04 May '05

Hello, I hope these don't turn out to be RTFM questions, but I can't find them in my FM :-) 1) Is there a function to get the ith element from an array? 2) Is there a function to get the "index" of an entry in an array? I've implemented these two functions below: 1) find 0 (x:xs) = x find n (x:xs) = find (n-1) xs 2) index i (x:xs) = if i == x then 0 else 1 + index a xs This was a fun exercise, but I can't shack off the feeling that I just re-invented the wheel. I need these because I want to be able to swap any two elements from an array. This is my swap function: -- swap i j array => swaps the ith and jth elements of 'array'. -- swap i j arr = a_head ++ [item_j] ++ a_midd ++ [item_i] ++ a_tail where a_head = [a | a <- arr, index a arr < i] item_i = find i arr a_midd = [a | a <- arr,(index a arr > i) && (index a arr < j)] item_j = find j arr a_tail = [a | a <- arr, index a arr > j] I'm sure this was a poor way to accomplish this, but it was a learning experience. If anyone would like to show me a more elegant solution, I would be happy to see it. Cheers, Daniel. Haskell newbie.

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Clarification on proof section of HS: The Craft of FP
by Echo Nolan 04 May '05

04 May '05

Hello all, My copy of HS: The Craft Of FP just arrived and I was reading section 8.5 about induction. On page 141, Simon Thompson gives a method of proving properties of functions on lists: 1) Prove that the property holds for the null list 2) Prove that the property holds for (x:xs) under the assumption that the property holds for xs. My question is this: what is the proof of (P([]) and ( P(xs) => P(x:xs))) => P(xs)? In other words, how does proof of the property on empty lists and proof that the property holds on (x:xs) under the assumption that it holds on xs give proof that it holds on all lists? Isn't there a recursive dependency here? You are defining the proof for lists with at least one element based on the assumption that it holds for all lists, right? How does this get you a proof of the general property if it depends on the assumption of the general property? Regards and thanks, Echo Nolan.

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How to join two lists of lists?
by Khrystyna Mandziy 03 May '05

03 May '05

Hi all! I'm trying to join to lists of lists. The problem is, i would like to get a new list of lists of tuples and not list of tuples of lists (that what zip makes). list1 = [[1,2],[3,4],[5,6]] list2 = [[a,b],[c,d],[e,f]] desiredlist = [[(1,a),(2,b)],[(3,c),(4,d)],[(5,e),(6,f)]] Thanks for any help!

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