[Haskell-cafe] Conditional lens
Hello! I am working with TypeReps, and while writing some functions I have noticed that I could use lenses to simplify them; however, I have stumbled upon some difficulties. First I’ll try to clarify which functions I want to write: * a function for converting TypeRep of, say, `Maybe x` to `[x]` (for all x). It requires checking if the TyCon is `Maybe` and replacing it with []-TyCon. If it wasn’t `Maybe`, I return Nothing. * a similar function for replacing `Char`s and `Lazy.Text`s to just `Text`. Again, if the TypeRep-to-be-replaced doesn’t satisfy my conditions, I return Nothing. These two functions (and some others, I suppose) can be written concisely with the help of one combinator. I don’t know how to write it as a composable Lens, so I’ll give it here as an ad-hoc Lens-modifying function instead: ifL :: (a - Bool) - Lens s t a b - Lens s (Maybe t) (Maybe a) b ifL p l = lens getter setter where get s = getConst $ l Const s getter s = let a = get s in if p a then Just a else Nothing setter s b = let a = get s in if p a then Just (set l b s) else Nothing It works like this: (0, 2) ifL even fs .~ hello Just (hello,2) (1, 2) ifL even fs .~ hello Nothing With `ifL`, my initial ugly changeTyCon :: TyCon - TyCon - TypeRep - Maybe TypeRep changeTyCon tc tc' t | t^.tyCon == tc = Just $ t tyCon .~ tc' | otherwise = Nothing boils down to changeTyCon tc tc' = ifL (== tc) tyCon .~ tc' Why did I call the initial version “ugly”? Well, because a) it manually handles `Maybe`s, and b) it has to perform both getting and setting (two passes). So, my questions are: 1. What would be the idiomatic way to write `ifL`? 2. How can I do something like `t ^. ifL (== tc) tyCon`? Currently it doesn’t work because view’s type has been simplified in lens-3.9. 3. Perhaps it would be better to represent `ifL` as a Traversal which simply ignores values that don’t match the condition? Then I could (?) use `failover` to do what I want. I searched for something filter-like in lens library, but haven’t found anything. 4. If I haven’t missed anything and it indeed can’t be done with bare lens, would `ifL` or something similar be welcome as an addition to the library? Thanks! ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Bytestring map/zipWith rationale
On Thu, 12 Sep 2013 18:24:24 +0400, Tom Ellis tom-lists-haskell-cafe-2...@jaguarpaw.co.uk wrote: On Thu, Sep 12, 2013 at 09:21:20AM -0400, Scott Lawrence wrote: Something's always bothered me about map and zipWith for ByteString. Why is it map :: (Word8 - Word8) - ByteString - ByteString but zipWith :: (Word8 - Word8 - a) - ByteString - ByteString - [a] Well, what if you wanted to zipWith a function of type Word8 - Word8 - Foo instead of Word8 - Word8 - Word8? Then why doesn’t map take “Word8 - a”, but only “Word8 - Word8”? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Proposal: New syntax for Haskell
On Wed, 11 Sep 2013 00:20:26 +0400, Thiago Negri evoh...@gmail.com wrote: I hope these jokes do not cause people to be afraid to post new ideas. Agreed. I would also like to clarify that my message was much more a joke on the incomprehensibility of legal acts than on the original proposal. By the way, I am pretty impressed with this piece of Cucumber description/code: Scenario: Mislav creates a valid task with an upload When I go to the Awesome Ruby Yahh task list page of the Ruby Rockstars project When I follow + Add Task And I fill in Task title with Ohhh upload And I follow Attachment When I attach the file features/support/sample_files/dragon.jpg to upload_file And I press Add Task And I wait for 1 second And I should see Ohhh upload as a task name I was much more sceptical when I had only seen the example in Niklas’s message. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Proposal: New syntax for Haskell
This might do for businesses, but clearly not adequate if we want Haskell/Cucumber (ever) to be suitable for use in government. Here I’d like to suggest a more rigorous approach, which hopefully will be considered for implementation instead of the original proposal. MODULE Data.List 1st proposal To promote prosperity, creativity, entrepreneurship, and innovation by providing convenient functions operating on lists, and for other purposes. IN THE STANDARD LIBRARY OF HASKELL September 10, 2013 Mr. KAZAK of Russia, Saint-Petersburg (for himself and Mr. GEHR, Mr. HAMBÜCHEN, Mr. WIEGLEY, Mr. ZIMMERMAN, Mr. CHEPLYAKA, Mr. ROSS, Mr. SNOYMAN, Mr. NEGRI, Mr. YANG and Mr. FUJIMURA) introduced the following module; which was referred to the Café of Haskell. A MODULE Be it approved by the General Public and Maintainers of `base` package, SECTION ONE. SHORT TITLE; TABLE OF CONTENTS === (a) Short Title - This Module may be cited as the ‘Data.List module’. (b) Table of Contents - The table of contents of this Module is as follows: Sec. 1. Short title; table of contents. ... TITLE I - HISTORY AND BACKGROUND Sec. 101. Definitions. Sec. 102. Action by Simon Peyton-Jones to protect Haskell users and prevent success at all costs¹. Sec. 103. Immunity for taking voluntary action against LANGUAGE pragmas dedicated to theft of syntax. Sec. 104. Immunity for taking voluntary action against libraries that make heavy use of unsafePerformIO. Sec. 105. Guidelines and study. Sec. 106. Denying `base` maintainership to notorious Applicative = Monad proposal supporters. TITLE II — THE ‘FOLDL’ FUNCTION --- Sec. 201. Type of ‘foldl’. Sec. 202. Specification of ‘foldl’. Sec. 203. Implementation of ‘foldl’. END OF TABLE OF CONTENTS TITLE I — HISTORY AND DEFINITIONS SEC. 101. DEFINITIONS. In this title: (1) FUNCTION - The term ‘function’ has the meaning implied in the Haskell 98 Report, even though it isn’t actually given there. (2) LIST - The term ‘list’ means a datatype used to provide the means of accessing data stored in it sequentially, starting with the first element and moving to the next element without delay, i.e. in O(1) time. (3) EMPTY LIST — The term ‘empty list’ denotes a list which does not contain any data, explicitly or implicitly, and which restricts any of the attempts to obtain its first element through the well-defined mechanism of exceptions and compile-time pattern match failures. (3) NON-EMPTY LIST - The term ‘non-empty list’ means a list which is not an empty list. ... TITLE II — THE ‘FOLDL’ FUNCTION SEC. 201. TYPE OF ‘FOLDL’ For any types A and B, be they sum types, product types, a valid combination of sum and/or product types; types defined in the Standard Library, defined by users of Haskell or defined in one of the Imported Modules; resulting from execution of Template Haskell; from execution of a generator written in another programming language, not excluding Haskell; or written by human(s): (a) function ‘foldl’ requires an argument which itself must be a function: (1) which requires an argument of type A and shall produce a function: (2) which requires an argument of type B and shall produce a value of type A. (b) and shall produce a function: (1) which requires an argument of type A and shall produce a function: (2) which requires an argument of type, which denotes the set of all lists, empty or non-empty, together with bottom and further abominations, which shall contain elements of type B, and shall produce a value of type A. SEC. 202. SPECIFICATION OF ‘FOLDL’ Assuming the following: (a) the argument of ′foldl’ is denoted by ‘f’. (b) the argument of the produced function is denoted by ′acc’. (c) the argument of the function, produced by the produced function, is denoted by ‘l’. Then it shall be held that: (a) ‘foldl’ must be using ‘f’ while processing the elements of ‘l’, and it may not use any other function, either supplied to it implicitly or explicitly, defined in Data.List module, other modules included into Standard Library, Hackage or any other collection of modules. (1) Other functions may be defined for internal use by ‘foldl’, but they shall not be used to replace ‘f’, as it is deemed highly unlikely that any of such defined functions are adequate replacements of ‘f’ and do not attempt to invade any country through means of launching missiles. (b) ‘foldl’ must process ‘l’ as follows: (1) it
[Haskell-cafe] Impredicative types and Lens?
Here’s a small example, which, when compiled, gives an error. Why?
{-# LANGUAGE FlexibleInstances, ImpredicativeTypes,
TemplateHaskell #-}
import Control.Lens
class Item a where
name :: a - String
instance Item (String, Int) where
name = fst
type ItemFilter = Item a = a - Bool
data ItemBox = ItemBox { _itemFilter :: ItemFilter }
makeLenses ''ItemBox
The error is
Couldn't match type `a0 - Bool'
with `forall a. Item a = a - Bool'
Expected type: ItemFilter
Actual type: a0 - Bool
In the expression: b_aaZE
In the first argument of `iso', namely
`\ (ItemBox b_aaZE) - b_aaZE'
In the expression: iso (\ (ItemBox b_aaZE) - b_aaZE) ItemBox
I’m using GHC 7.6.2, if it’s important.
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Re: [Haskell-cafe] Array, Vector, Bytestring
Oops. Ben Gamari bgamari.f...@gmail.com писал(а) в своём письме Tue, 04 Jun 2013 04:41:53 +0300: To be perfectly clear, ByteString and Text target much different use-cases and are hardly interchangeable. While ByteString is, as the name suggests, a string of bytes, Text is a string of characters in a Unicode encoding. When you are talking about unstructured binary data, you should most certainly be using ByteString. Why create a special case? Right now you should use ByteString, yes, but I wish I could just use a generic array of Word8. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Array, Vector, Bytestring
silvio silvio.fris...@gmail.com писал(а) в своём письме Mon, 03 Jun 2013 22:16:08 +0300: Hi everyone, Every time I want to use an array in Haskell, I find myself having to look up in the doc how they are used, which exactly are the modules I have to import ... and I am a bit tired of staring at type signatures for 10 minutes to figure out how these arrays work every time I use them (It's even worse when you have to write the signatures). I wonder how other people perceive this issue and what possible solutions could be. Recently I’ve started to perceive this issue as “hooray, we have lenses now, a generic interface for all the different messy stuff we have”. But yes, the inability to have One Common API for All Data Structures is bothering me as well. Why do we need so many different implementations of the same thing? In the ghc libraries alone we have a vector, array and bytestring package all of which do the same thing, as demonstrated for instance by the vector-bytestring package. To make matters worse, the haskell 2010 standard has includes a watered down version of array. Indeed. What we need is `text` for strings (and stop using `bytestring`) and reworked `vector` for arrays (with added code from `StorableVector` — basically a lazy ByteString-like chunked array). # Index I don't really see a reason for having an index of a type other than Int and that starts somewhere else than at 0. It’s a bad idea. I, for one, don’t really see how writing `Vector (Vector (Vector Int))` can be considered even remotely satisfying by anyone. And if you’re considering 3D arrays “a corner case”, then I’m afraid I can’t agree with you. Also, arrays which allow negative indexing can save a lot of headache and prevent mistakes which generally occur when a programmer is forced to constantly keep in mind that index 2000 is actually 0 and 0 is −2000. # Storable vs Unboxed Is there really a difference between Storable and Unboxed arrays and if so can't this be fixed in the complier rather than having to expose this problem to the programmer? Storable seems to be mainly for marshalling, and most people who need it are (probably) library writers. I don’t know for sure, though, but it doesn’t appear to be a big issue. # ST s vs IO This is probably the hardest to resolve issue. The easiest solution is probably to just have a module for each of them as in the array package. I find the PrimState a bit complicated and circuitous. The ideal solution would be to have type IO a = ST RealWorld# a in the next haskell standard. Sure, except that IO is actually *not* ST+Realworld, and only happens to be implemented like that in GHC (not in JHC, for instance). It has been discussed before: http://haskell.1045720.n5.nabble.com/IO-ST-RealWorld-td3190075.html . (Not to mention people attempting to rewrite RealWorld# values and create havoc and fire missiles everywhere expecting them to disappear the very moment they smile knowingly and `put` the original RealWorld# back.) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] data types with overlapping component names (in one module)?
I'll just leave it here: http://hackage.haskell.org/trac/ghc/wiki/Records ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ifdef based on which OS you're on
Andrew Cowie and...@operationaldynamics.com писал(а) в своём письме Fri, 15 Feb 2013 17:05:13 +0300: So my question is: what's an appropriate Haskell mechanism for building code that is OS / arch / distro specific? It's not like I have autoconf running generating me a config.h I could #include, right? You can know the OS and arch without even resorting to CPP; see System.Info (http://hackage.haskell.org/packages/archive/base/latest/doc/html/System-Info.html), which defines `os` and `arch`. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How far compilers are allowed to go with optimizations?
Ouch, forgot the Cafe. Would you object to this particular optimisation (replacing an algorithm with an entirely different one) if you were guaranteed that the space behaviour would not change? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] list comprehansion performance has hug different
Junior White efi...@gmail.com писал(а) в своём письме Tue, 29 Jan 2013 12:25:49 +0300: The only different in the two program is in the first is q - [1..n], qs - queens' (k-1), and the second is qs - queens' (k-1), q - [1..n]. In the first case `queens' (k-1)` is being recomputed for every q (that is, n times). Of course it would matter :) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] list comprehansion performance has hug different
Junior White efi...@gmail.com писал(а) в своём письме Tue, 29 Jan 2013 12:40:08 +0300: Hi Artyom, Thanks! But I don't understand why in the first case queens' (k-1) is being recomputed n times? Because your list comprehension is just a syntactic sugar for concatMap (\q - concatMap (\qs - if isSafe q qs then [q:qs] else []) (queens' (k-1))) [1..n] Here `queens' (k-1)` does not depend on `qs`, and therefore it *could* be floated out of the lambda: let queens = queens' (k-1) in concatMap (\q - concatMap (\qs - if isSafe q qs then [q:qs] else []) queens) [1..n] But it is an unsafe optimisation. Suppose that the `queens` list is very big. If we apply this optimisation, it will be retained in memory during the whole evaluation, which may be not desirable. That’s why GHC leaves this to you. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] list comprehansion performance has hug different
Junior White efi...@gmail.com писал(а) в своём письме Tue, 29 Jan 2013 12:59:31 +0300: So this is a problem in lazy evaluation language, it will not appear in python or erlang, am i right? Not quite. Compilers of imperative languages don’t perform CSE (common subexpression elimination) either; `queens' (k-1)` could have some side effects, after all, and performing a side effect only once instead of n times is a definite bug. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] quotRem and divMod
Shachaf Ben-Kiki shac...@gmail.com писал(а) в своём письме Tue, 29 Jan 2013 09:09:37 +0300: That code is from base 4.5. Here's base 4.6: quotRem x@(I32# x#) y@(I32# y#) | y == 0 = divZeroError -- Note [Order of tests] | y == (-1) x == minBound = (overflowError, 0) | otherwise = case x# `quotRemInt#` y# of (# q, r #) - (I32# (narrow32Int# q), I32# (narrow32Int# r)) So it looks like it was improved in GHC 7.6. In particular, by this commit: http://www.haskell.org/pipermail/cvs-libraries/2012-February/014880.html Shacha Well, I’m glad to know that it has been fixed in the newer GHC (I’m still on 7.4). Thanks! ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] quotRem and divMod
Hi! I’ve always thought that `quotRem` is faster than `quot` + `rem`, since both `quot` and `rem` are just wrappers that compute both the quotient and the remainder and then just throw one out. However, today I looked into the implementation of `quotRem` for `Int32` and found out that it’s not true: quotRem x@(I32# x#) y@(I32# y#) | y == 0 = divZeroError | x == minBound y == (-1) = overflowError | otherwise = (I32# (narrow32Int# (x# `quotInt#` y#)), I32# (narrow32Int# (x# `remInt#` y#))) Why? The `DIV` instruction computes both, doesn’t it? And yet it’s being performed twice here. Couldn’t one of the experts clarify this bit? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cannot read a large integer on linux
Right, it was fixed in GHC 7.4.2. hackage.haskell.org/trac/ghc/ticket/5688 The trouble with old behaviour was that it had been creating a security breach (anybody could pass 1e1000 where an Integer was expected and cause a segmentation fault). 15.01.2013 2:41 пользователь Arnaud Bailly arnaud.oq...@gmail.com написал: Hello, I am encountering a strange issue while trying to read a string into an integer. On windows 7 64bit, I have: read 18780189038289e49 :: Integer =187801890382890 On linux (64bit, libgmp.so.3.5.2) I have: read 18780189038289e49 :: Integer *** Exception: Prelude.read: no parse That's weird and I really have no clue what's going on. I use ghci 7.4.2 on linux and 7.4.1 on windows. What am I doing wrong ? Arnaud ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Gloss and relatively expensive computations
You could create a new thread which would be 'forever' executing your extensive computation and updating some IOVar accordingly. The drawing function would do nothing except reading that IOVar and displaying its contents. Since drawing is cheap, this can be done at any reasonable rate. 28.12.2012 3:22 пользователь Daniel Díaz Casanueva dhelta.d...@gmail.com написал: Hello cafe! I'm having some performance issues trying to use gloss to make animations where each model step is relatively time expensive. I'm using the IO.Simulate module because my step function needs to do an IO operation which takes around 1 second (it may vary). I will try to give some details. I have the step function: step :: Model - IO Model step m = do ... p - slowOperation ... return newModel The rest of the program is small and simple. The drawing function (Model - IO Picture -- it is pure though) is as quick as simple. However, the program get stuck after the first iteration. In the other hand, I am using the animateIO function which ask me for an Int value to set up the number of simulation steps to take for each second of real time. But I'm more interested in the animation waiting for the simulation step to end. Does it make sense? I would be really thankful with any pointer here. Thanks in advance, Daniel Díaz. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] edge: compile testing
Compiled just fine on my machine. Ubuntu 12.10, Haskell Platform 2012.2.0.0, GHC 7.4.2, cabal-install 1.16.0.1. Christopher Howard christopher.how...@frigidcode.com писал(а) в своём письме Sat, 15 Dec 2012 06:52:22 +0300: Hey guys, to teach myself Haskell I wrote a little arcade game called The Edge, built on gloss. It is in hackage under the package name edge. Are there a few kind souls who would be willing to compile it on their machines and let me know if there are any problems at the compiling level? In the past, I've had issues with Haskell code compiling fine on my development system but not on others (due to dependency-related issues). I want to double check this before I try to make any distro-specific packages. I developed with GHC 7.4 and cabal-install 1.16.0.2 on a Gentoo system. Requires OpenGL and OpenAL (for sound). cabal update cabal install edge ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] isLetter vs. isAlpha
Hello! I saw a question on StackOverflow about the difference between isAlpha and isLetter today. One of the answers stated that the two functions are interchangeable, even though they are implemented differently. I decided to find out whether the difference in implementation influences performance, and look what I found: import Criterion.Main import Data.Char fTest name f list = bgroup name $ map (\(n,c) - bench n $ whnf f c) list tests = [(latin, 'e'), (digit, '8'), (symbol, '…'), (greek, 'λ')] main = defaultMain [fTest isAlpha isAlpha tests, fTest isLetter isLetter tests] produces this table (times are in nanoseconds): latin digit symbol greek - - -- - isAlpha | 156 212 368310 isLetter | 349 344 383310 isAlpha is twice as fast on latin inputs! Does it mean that isAlpha should be preferred? Why isn’t isLetter defined in terms of isAlpha in Data.Char? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] List all multiply/add combinations
Jonas Almström Duregård jonas.dureg...@chalmers.se писал(а) в своём письме Mon, 19 Nov 2012 01:31:01 +0300: Hi, You can make a datatype that captures exactly the expressions you want (see code below). Essentially you want to make sure that a subtraction or addition never has another subtraction or addition as its left operand. I would also like to advertise a bit and show how this type can be enumerated automatically by Feat ( http://hackage.haskell.org/package/testing-feat). After a quick look, Feat seems to be awesome. Thanks! I don’t yet know how I am going to use it, but I hope an opportunity will present itself soon :) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] List all multiply/add combinations
Instead of attacking the problem textually, try to create a datatype which would describe your expressions, then generate all values of this datatype, filter those you don’t need, and convert the rest into Strings. Currently your expressions are represented by “String” — conversion is very cheap, but filtering is “hard” (since it boils down to parsing). Binary trees would suit you better. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] List all multiply/add combinations
Sorry! I replied without reading your message properly. I could then work directly with parsing trees, and generate all binary trees of fixed lengths. But most of them would be unnecessary, so it seems like I'm attacking it from the wrong angle. They won’t be unnecessary if you generate them in a right way. I will think about it and reply with a detailed answer as soon as possible. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] List all multiply/add combinations
The following algorithm generates all possible expressions and throws away most of unnecessary duplicates. import qualified Data.Map as M data Expr = Num Int | Add Expr Expr | Sub Expr Expr | Mul Expr Expr | Div Expr Expr Rendering function is highly imperfect. Either write one yourself, or change the definition of Expr to something like “Num Int | App Op [Expr]” — this way rendering would become much easier. render :: Expr - String render (Num n) = show n render (Add a b) = ( ++ render a ++ + ++ render b ++ ) render (Sub a b) = ( ++ render a ++ - ++ render b ++ ) render (Mul a b) = ( ++ render a ++ * ++ render b ++ ) render (Div a b) = ( ++ render a ++ / ++ render b ++ ) Let’s assume that we have lN numbers. nums = [1, 2, 3] lN = length nums Our goal is to build table of all possible expressions, which can be build using numbers from i-th to j-th, where i, j are in range from 0 to lN-1. We have to fill the table in the following order: numbers themselves, expressions consisting of two numbers, three, four, … N. table :: M.Map (Int, Int) [Expr] table = M.fromList $ [((i, i), [Num n] ) | (i, n) - zip [0..lN-1] nums] ++ [((i, j), calc i j) | i - [0..lN-1], j - [i+1,i+2..lN-1]] answer = table M.! (0, lN-1) Our next goal is a function which fills this table: calc :: Int - Int - [Expr] calc i j = do --elements from i to k will form one branch, k+1 to j — another k - [i,i+1..j-1] le - table M.! (i, k) re - table M.! (k+1, j) We don’t want to generate both (a+b)+c and a+(b+c), or (a+b)-c and a+(b-c), or (a-b)-c and a-(b+c), or (a-b)+c and a-(b-c), so we’re eliminating the second variant in each pair. Multiplication and division follow the same pattern. case re of Add _ _ - [Mul le re, Div le re] Sub _ _ - [Mul le re, Div le re] Mul _ _ - [Add le re, Sub le re] Div _ _ - [Add le re, Sub le re] otherwise - [Add le re, Sub le re, Mul le re, Div le re] Here are generated expressions: 1*(2+3) 1/(2+3) 1*(2-3) 1/(2-3) 1+(2*3) 1-(2*3) 1+(2/3) 1-(2/3) (1+2)+3 (1+2)-3 (1+2)*3 (1+2)/3 (1-2)+3 (1-2)-3 (1-2)*3 (1-2)/3 (1*2)+3 (1*2)-3 (1*2)*3 (1*2)/3 (1/2)+3 (1/2)-3 (1/2)*3 (1/2)/3 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] List all multiply/add combinations
Indentation messed up… I have pasted the code here: http://hpaste.org/77864 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Polyvariadic composition
Hello,
I have accidentally written my version of polyvariadic composition
combinator, `mcomp`. It differs from Oleg’s version (
http://okmij.org/ftp/Haskell/polyvariadic.html#polyvar-comp ) in three
aspects: a) it is simpler, b) it works without enumerating basic cases
(all existing types, in other words), and c) it needs more type extensions.
{-# LANGUAGE
MultiParamTypeClasses
, FunctionalDependencies
, FlexibleInstances
, UndecidableInstances
, TypeFamilies , OverlappingInstances
#-}
class Mcomp a ar b br | a br - b where
mcomp :: a - (ar - br) - b
instance (a ~ ar, b ~ br) = Mcomp a ar b br where
mcomp a f = f a
instance (Mcomp a ar b br) = Mcomp (x - a) ar (x - b) br where
mcomp a f = \x - mcomp (a x) f
My question is: why doesn’t it work when I replace
instance (a ~ ar, b ~ br) = Mcomp a ar b br
with
instance Mcomp a a b b
? I thought that equal letters mean equal types…
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Re: [Haskell-cafe] Detecting numeric overflows
Евгений Пермяков permea...@gmail.com писал в своём письме Mon, 30 Jul 2012 09:47:48 +0300: Can someone tell me if there are any primitives, that used to detect machine type overflows, in ghc haskell ? I perfectly understand, that I can build something based on preconditioning of variables, but this will kill any performance, if needed. In GHC.Prim — primitives addIntC# and subIntC#: addIntC# :: Int# - Int# - (#Int#, Int##) Add with carry. First member of result is (wrapped) sum; second member is 0 iff no overflow occured. subIntC# :: Int# - Int# - (#Int#, Int##) Subtract with carry. First member of result is (wrapped) difference; second member is 0 iff no overflow occured. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Importing modules in GHCi
Hi Café, I would greatly appreciate your help. Entering the following in GHCi produces an error message… -- import Data.Time -- getCurrentTime = print interactive:1:20: No instance for (Show UTCTime) arising from a use of `print' Possible fix: add an instance declaration for (Show UTCTime) In the second argument of `(=)', namely `print' In the expression: getCurrentTime = print In an equation for `it': it = getCurrentTime = print …but when I create a file with `import Data.Time` in it, and load the file in GHCi, everything works as expected. Is it a bug in GHCi, or a feature? I’m using Haskell Platform 2012.2.0.1. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Importing modules in GHCi
Oh, I’m sorry. I have Haskell Platform 2011.2.0.1, not 2012.2.0.1. So I guess it was a bug in GHCi… ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Problem with packet documentation generated by cabal on windows 7
I’m having the same problem on my Windows 7 laptop. The solution I’ve found is to use Internet Explorer — it isn’t perfect, but for some reason it is the only browser capable of handling these links. On Fri, May 25, 2012 at 01:19:11AM +0200, Nicu Ionita wrote: Hi cafe, I have a problem with haddock documentation created when installing new packages with cabal on windows. The generated html files have all links in the form j:\Users\...\doc\...\xxx.html, but firefox says, it cannot open that link. Actually all links should be prefixed by file:///. I wonder if this is only on windows so and if there is a solution to this. Is there a cabal or haddock flag for this? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] (+1) vs let inc=(+1)
http://www.haskell.org/haskellwiki/Monomorphism_restriction ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] A functional programming solution for Mr and Mrs Hollingberry
Challenge accepted! I have written a solution in Haskell; please merge :) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] A functional programming solution for Mr and Mrs Hollingberry
Andreas Pauley apau...@gmail.com писал(а) в своём письме Sun, 20 May 2012 20:33:13 +0300: I want to see how elegant a solution I can get in a functional language, given that the problem description is not really elegant at all. It has a few annoying exceptions to the normal rules, typical of what one might get in a real specification from some client. After taking a look at other solutions, I feel like I will have to explain myself, so I’d better do that without prompting :) - nothing was said about meaningful error messages, so I didn’t bother. - I had decided against defining constants like `supplier_markup_percentage_modification` separately; `PremiumSupplierIDs` and markup table are defined locally in the `calc` function, too. The latter two issues are fixed in the next version, as someone may consider them to be against elegance. - surprisingly, all solutions use explicit comparisons to determine the product category. While it is okay for continuous ranges of codes, it doesn’t scale and not really elegant. Fixed as well. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Unboxed Rationals?
Yves Parès limestr...@gmail.com писал(а) в своём письме Thu, 12 Jan 2012 13:14:16 +0200: uvector is deprecated, its functionnalities has been ported into vector. Yes, but a Ratio a instance hasn't been ported. I admit that I have overlooked the “deprecated” warning, and agree that it is better to write an instance by yourself than use a deprecated package. Dead things should stay dead. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Unboxed Rationals?
You can use Data.Vector.Unboxed. There isn't an instance for Ratio a, but it is easy to write one, since it would be very similar to Complex a. http://hackage.haskell.org/packages/archive/vector/0.9.1/doc/html/Data-Vector-Unboxed.html#t:Unbox ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Unboxed Rationals?
Also, uvector already supports unboxed Ratios: http://hackage.haskell.org/package/uvector In fact, I am surprised that Data.Vector doesn't have a Ratio instance, but has a Complex instance. Any ideas, why? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] On the purity of Haskell
Gregg Reynolds d...@mobileink.com писал(а) в своём письме Fri, 30 Dec 2011 17:23:20 +0200: Regarding side-effects, they can be (informally) defined pretty simply: any non-computational effect caused by a computation is a side-effect. I wonder: can writing to memory be called a “computational effect”? If yes, then every computation is impure. If no, then what’s the difference between memory and hard drive? By the way, the Data.HashTable is in IO monad. Is it impure? Would it be pure if designers had chosen to use ST instead? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] On the purity of Haskell
Donn Cave d...@avvanta.com писал(а) в своём письме Fri, 30 Dec 2011 20:36:46 +0200: That's why we use terms in a sense that apply meaningfully to computer programming languages in general and Haskell in particular. To do otherwise - for example to insist on a definition of pure that could not even in principle apply to any useful programming language, or a definition of side effect that would have to apply every time a program does anything - seems to me like an inane waste of time, to put it mildly. When one questions accepted definitions or beliefs, it is the sign of their vagueness. To be honest, the definitions of “side effect” and “purity” are vague indeed. I hope that eventually (probably in this very discussion) they will be refined. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] On the purity of Haskell
Chris Smith cdsm...@gmail.com писал(а) в своём письме Fri, 30 Dec 2011 22:04:21 +0200: Computability is just a distraction here. The problem isn't whether getAnIntFromUser is computable... it is whether it's a function at all! Even uncomputable functions are first and foremost functions, and not being computable is just a property that they have. Clearly this is not a function at all. It doesn't even have the general form of a function: it has no input, so clearly it can't map each input value to a specific output value. Now, since it's not a function, it makes little sense to even try to talk about whether it is computable or not (unless you first define a notion of computability for something other than functions). Of course getAnIntFromUser is not a function. It is an instruction to computer. Think of IO as a form of writing instructions to some worker (essentially, the kernel, which in its turn uses processor's io ports). You are asking this “worker” to change some global state. Thus, your function “f” is a function indeed, which generates a list of instructions to kernel, according to given number. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] On the purity of Haskell
Chris Smith cdsm...@gmail.com писал(а) в своём письме Fri, 30 Dec 2011 22:28:36 +0200: I really think that the notion of “purity” appeared to convince C programmers. It would be silly to try to explain that “Int - IO Int” isn't really a function from Int to Int, monads, blah blah blah. So, we're saying: “here is a function which accepts Int and (sic!) returns Int, but it can also do IO, which is kinda unsafe. So we are marking it with ‘IO’ letters, see? This means that this function is ‘impure’. And to prevent mixing pure things with impure things, compiler demands you to mark with IO every “function” which ‘uses’ IO”. Functions don't use IO. Funtions return IO something. And functions returning IO are impure. That's all. This is a valid concern... assigning a meaning to values of IO types necessarily involves some very unsatisfying hand-waving about indeterminacy, since for example IO actions can distinguish between bottoms that are considered equivalent in the denotational semantics of pure values (you can catch a use of 'error', but you can't catch non-termination). Nevertheless, I'm satisfied that to the extent that any such meaning can be assigned, f will be a valid function on non-bottom values. Not perfect, but close. Agree. The fact that IO actions can distinguish between bottoms, self-modify code, terminate non-terminable computations by rebooting the system, send killbots to the programmer's house and so on are extremely unsatisfying. That's IO for you. The dirty impure bottom comparison which uses IO, though, is available only to already impure functions. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] I've just heard of a neat security measure that when you compile the code it generates different object code...
I wonder, if there is any example of actual Haskell program cracked / reverse engineered? GHC-generated code is already quite hard to understand… ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Strange GC timings
Hello! The following program executes 1.5 seconds on my computer: ---CODE BEGIN- module Main where import Data.Array.IArray main = print (answers ! 100) nextAns :: (Int, Int, Float) - (Int, Int, Float) nextAns (a, n, r) = if r2 1 then (a+1, n+2, r2) else (a+1, n+3, r3) where a' = fromIntegral a n' = fromIntegral n r2 = r * (a'/(a'+1))**n' * (n'+1)*(n'+2)/(a'+1)^2 r3 = r2 * (n'+3) / (a'+1) answers :: Array Int Int answers = listArray (1, 100) (map snd3 $ iterate nextAns (1, 2, 2)) where snd3 (a, b, c) = b CODE END-- From these 1.5 seconds, 1 second is spent on doing GC. If I run it with -A200M, it executes for only 0.5 seconds (total). Which is more interesting, when I use UArray instead of Array, it spends only 0.02 seconds in GC, but total running time is still 1.5 seconds. Why are... these things? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Bounds checking pragma?
2011/11/10 Daniel Fischer daniel.is.fisc...@googlemail.com:
There's a problem here, unsafeAt uses an Int index into the array, while
(!) uses the declared index type. Even skipping the bounds check, you'd
still have to calculate the Int index for the replacement of (!).
#ifdef OMIT_BOUNDS_CHECK
{-# RULES
ArrayIndex arr ! i = unsafeAt arr (unsafeIndex (bounds arr) i)
#-}
#endif
Thanks!
(?) = unsafeAt
Yes, but (!) was taken as an example. There is a lot of other
functions doing bounds checking... Creating replacements for every
single function is rather tedious.
The flag pragma also has other uses. For example, we can introduce an
overflow flag (check every operation with Int's for overflow) ,
which may be useful for debugging. In release version this flag will
be turned off.
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[Haskell-cafe] Bounds checking pragma?
Hello!
The (!) operator is short and nice. Unfortunately, when doing heavy
computing, we have to use unsafeAt instead. It looks ugly and it is
ugly, also.
Some compilers for imperative languages like Free Pascal have an option to
turn on/off bounds checking for arrays. Wouldn't it be nice to have such
option in GHC? Is it possible?
There is a problem: Haskell has a lot of array libraries. The only
solution I see is a new FLAG pragma:
(!) :: Array i a - i - a
--definition
{-# FLAG boundsCheck (!) = unsafeAt #-}
It is similar to RULES pragma, but only fires when flag is set. To set the
flag you need to complile with option -flags=boundsCheck. Also, the
mantainers of vector library, bytestring library, repa library and so on
will have to include such pragmas in their code.
I don't know about C++ preprocessor, though. Maybe this is already
solvable with #define's...
Anyway, I have to say it once again: unsafeAt is ugly and Haskell is
beautiful. Why high-performance code should be ugly?
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[Haskell-cafe] Additional functions of GMP
GMP has a lot of functions, such as extracting roots, primality test, Legendre symbol, factorial and so on. These can be written in Haskell, of course, but isn't it better to use existing functions? They are also much faster than similar functions from NumericPrelude, I believe. I have heard GHC 7.2.1 now includes module named GHC.Integer.Logarithms, but I can't find its description anywhere. So, my question is: can I use full power of GMP's functions, and if I can — how? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Additional functions of GMP
I'm writing a package (arithmoi) that will include reasonably fast implementations of those, but I never find the time to finish it :( Package is great, but sometimes it is useful to have such functions out of box (for example, when solving SPOJ problems). No, you can't, unfortunately (not easily, anyway). I have found a manual on including additional primops in GHC (exactly this situation), but this requires modifying GHC's sources, which also does not allow using them with SPOJ. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Problem with GLUT - no visuals found
It may be related to the problem which I encountered too: http://www.mail-archive.com/haskell-cafe@haskell.org/msg89460.html Try using GLUT from http://github.com/haskell-opengl/GLUT Hope that helps. --Artyom ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Lazy Evaluation in Monads
Suppose iRecurse looks like this: iRecurse = do x - launchMissiles r - iRecurse return 1 As x is never needed, launchMissiles will never execute. It obviously is not what is needed. But in Haskell, standart file input|output is often lazy. It's a combination of buffering and special tricks, not the usual rule. Scott Lawrence byt...@gmail.com писал(а) в своём письме Tue, 31 May 2011 22:49:02 +0300: I was under the impression that operations performed in monads (in this case, the IO monad) were lazy. (Certainly, every time I make the opposite assumption, my code fails :P .) Which doesn't explain why the following code fails to terminate: iRecurse :: (Num a) = IO a iRecurse = do recurse - iRecurse return 1 main = (putStrLn . show) = iRecurse Any pointers to a good explanation of when the IO monad is lazy? === The long story === I wrote a function unfold with type signature (([a] - a) - [a]), for generating a list in which each element can be calculated from all of the previous elements. unfold :: ([a] - a) - [a] unfold f = unfold1 f [] unfold1 :: ([a] - a) - [a] - [a] unfold1 f l = f l : unfold1 f (f l : l) Now I'm attempting to do the same thing, except where f returns a monad. (My use case is when f randomly selects the next element, i.e. text generation from markov chains.) So I want unfoldM1 :: (Monad m) = ([a] - m a) - [a] - m [a] My instinct, then, would be to do something like: unfoldM1 f l = do next - f l rest - unfoldM1 f (next : l) return (next : rest) But that, like iRecurse above, doesn't work. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Lazy Evaluation in Monads
Scott Lawrence byt...@gmail.com писал(а) в своём письме Tue, 31 May 2011 23:29:49 +0300: On 05/31/2011 04:20 PM, Artyom Kazak wrote: Suppose iRecurse looks like this: iRecurse = do x - launchMissiles r - iRecurse return 1 As x is never needed, launchMissiles will never execute. It obviously is not what is needed. Prelude let launchMissiles = putStrLn UH OH return 1 Prelude let iRecurse = launchMissiles return 1 Prelude iRecurse UH OH 1 Prelude Looks like launchMissiles /does/ execute, even though x is (obviously) never needed. Oh, sorry. I was unclear. I have meant assuming IO is lazy, as Yves wrote. And saying some hacks I meant unsafeInterleaveIO, which lies beneath the laziness of, for example, getContents. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Reverse Show instance
And I can declare an instance for (x, y) which does NOT implies (Show x): instance Show (x, y) where show _ = I'm tuple! Hooray! Andrew Coppin andrewcop...@btinternet.com писал(а) в своём письме Fri, 20 May 2011 00:08:27 +0300: Cannot deduce (Show x) from context (Show (x, y)). Cannot deduce (Show y) from context (Show (x, y)). Um... seriously? From Prelude, we have Show x, Show y = Show (x, y) So clearly it works in the forward direction. But apparently not in the reverse direction. Is this a bug or a feature? (I.e., is there some obscure possibility I haven't thought of which means that doing the reverse inference would be incorrect?) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] I cannot find the module Data.Numbers.Primes
Yes, of course there is! You can find the index of all functions, types, typeclasses etc. here: http://lambda.haskell.org/hp-tmp/docs/2011.2.0.0/doc-index.html KC kc1...@gmail.com писал(а) в своём письме Tue, 17 May 2011 20:33:05 +0300: Is there a way to tell when a function is included in the standard Haskell Platform or when it needs to be loaded from Hackage? On Tue, May 17, 2011 at 9:08 AM, Benedict Eastaugh ionf...@gmail.com wrote: cabal install primes? http://hackage.haskell.org/package/primes https://github.com/sebfisch/primes ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] generic putback
I'm sorry, but I don't fully understand what do you want from putback. If putback'ed action does io and then returns x, it's trivial: putback x io = io return x If you want putback'ed action to return x on its first call and do io on second, third... calls, then you need to put somewhere a mark indicating that action was called. You can use IORefs. import Data.IORef import System.IO.Unsafe putback x io = do m - readIORef r if m then io else (writeIORef r True return x) where r = unsafePerformIO $ newIORef False Sergey Mironov ier...@gmail.com писал(а) в своём письме Sun, 15 May 2011 17:33:51 +0300: Hi Cafe. I wonder if it is possible to write a IO putback function with following interface putback :: a - IO a - IO a putback x io = ??? where io is some action like reading from file or socket. I want putback to build new action which will return x on first call, and continue executing io after that. Thanks in advance! Sergey. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] warning - Euler problem spoiler enclosed
Barbara Shirtcliff ba...@gmx.com писал(а) в своём письме Wed, 04 May 2011 16:41:07 +0300: Also, note that lexOrder s@[_] = [s] is nicer than lexOrder s | length s == 1 = [s]. I agree that that initial version was a little clumsy, but your suggestion doesn't really seem to work: lexOrder :: [Char] - [[Char]] lexOrder s@[_] = s lexOrder s = concat $ map (\n - h n) [0..((length z) - 1)] where z = sort $ nub s h :: Int - [String] h n = map (z!!n :) $ lexOrder $ filter (\c - lexI c z /= n) z Euler.hs:8:18: Couldn't match expected type `[Char]' with actual type `Char' Expected type: [[Char]] Actual type: [Char] In the expression: s In an equation for `lexOrder': lexOrder s@[_] = s It actually works, you have forgotten square brackets: lexOrder s@[_] = [s] --not s!. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] GLUT error while using Gloss
Hi Cafe! When I'm running examles from Gloss graphics library, all examples except gloss-hello are crashing with the following error: GLUT: Warning in gloss-easy: GL error: gloss-easy: stderr: hPutChar: invalid argument (character is not in the code page). A window with produced picture is showed for one second and then it crashes. gloss-hello, strangely, is working perfectly. I'm using Windows 7 (but on XP there is same behaviour), Haskell Platform 2011.2, OpenGL 2.4.0.1, GLUT 2.2.2.0, Gloss 1.3.1.2. At the first time, exampes didn't want to run at all, but I placed glut32.dll from http://www.xmission.com/~nate/glut.html in my .dlls folder. I tried another glut32.dll (from the Raincat game), but it didn't change anything. How can it be fixed? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GLUT error while using Gloss
It's good to hear. Thanks! 2011/5/2 Jason Dagit dag...@gmail.com: This is fixed in the git repository for GLUT, but I didn't push the fix to hackage yet: https://github.com/haskell-opengl/GLUT/pull/1 Sorry for the inconvenience! Jason ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to use roots package?
Oh. I have taken a wrong approach to the problem. I have written Newton method with cutting precision if it's more than N digits, and it finds an answer practically in no time. But still, it's very good, thank you! ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] How to use roots package?
Hi Café! roots (http://hackage.haskell.org/package/roots) is a package to solve equations like f(x)==0. In RootFinder class there is an 'defaultNSteps' value, which is used as maximal count of iterations functions like findRoot and traceRoot can make. By default it is 250, but sometimes it's not enough. How can I use another value instead of 250? Should I write my own RootFinder instance, or findRoot function? Thanks in advance. — Artyom. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How large is the Haskell community ?
Aaron Gray aaronngray.li...@gmail.com писал(а) в своём письме Sat, 12 Feb 2011 22:18:33 +0200: I was wondering if anyone had an idea or estimate as to how large the Haskell community is ? Aaron I've been subscribed to this list since the very start of the 2010 year, and I counted 1168 ± 20 different persons posting to this list (I just listed all the mail from Haskell-Cafe in my mail client and after 1.5 hours of work I counted them all, so I can be slightly mistaken). As only 1/2 of all haskellers post to the Cafe, and as I'm novice, I missed... OK, 6/7 of all haskellers (the number of haskellers grows over time, so there was little of them 10 years ago), 1200 * 2 * 7 = 16800 haskellers. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] A State Monad Tutorial
Some time ago I have read A State Monad Tutorial (http://strabismicgobbledygook.wordpress.com/2010/03/06/a-state-monad-tutorial/). While reading, I was fixing some minor mistakes (okay, a lot of mistakes). After all, I had an idea to create PDF with fixed version. So, here it is: http://dl.dropbox.com/u/8662438/A%20State%20Monad%20Tutorial.pdf ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Parallel Pi
Hello! I tried to implement the parallel Monte-Carlo method of computing Pi number, using two cores: --PROGRAM module Main where import Random import Data.Ratio import Data.List import System.IO import GHC.Conc main = do putStrLn pi 1 putStr n: hFlush stdout t - getLine piMonte (read t) = (putStrLn . show) piMonte n = do (g1, g2) - split `fmap` getStdGen let r1 = r (n `div` 2) g1 r2 = r (n `div` 2 + n `mod` 2) g2 in return (ratio (r1 `par` (r2 `pseq` (merge r1 r2 where r n g = (length (filter id lAll), n) where l = take n . randomRs (0, 1) inCircle :: Double - Double - Bool inCircle a b = a*a + b*b = 0.25 lAll = zipWith inCircle (l g1) (l g2) (g1, g2) = split g ratio :: (Int, Int) - Double ratio (a, b) = fromRational (toInteger a % toInteger b * 16) merge (a, b) (c, d) = (a + c, b + d) --END But it uses only on core: C:\ghc --make -threaded Monte.hs -fforce-recomp [1 of 1] Compiling Main ( Monte.hs, Monte.o ) Linking Monte.exe ... C:\monte +RTS -N2 -s monte +RTS -N2 -s pi 1 n: 100 3.143616 2,766,670,536 bytes allocated in the heap 1,841,300 bytes copied during GC 5,872 bytes maximum residency (1 sample(s)) 23,548 bytes maximum slop 2 MB total memory in use (0 MB lost due to fragmentation) Generation 0: 5285 collections, 5284 parallel, 0.64s, 0.31s elapsed Generation 1: 1 collections, 1 parallel, 0.00s, 0.00s elapsed Parallel GC work balance: 1.00 (454838 / 454676, ideal 2) MUT time (elapsed) GC time (elapsed) Task 0 (worker) :0.00s( 9.33s) 0.00s( 0.00s) Task 1 (worker) :0.63s( 9.33s) 0.00s( 0.00s) Task 2 (worker) :6.00s( 9.34s) 0.64s( 0.31s) Task 3 (worker) :0.00s( 9.34s) 0.00s( 0.00s) SPARKS: 1 (0 converted, 1 pruned) INIT time0.02s ( 0.00s elapsed) MUT time6.63s ( 9.34s elapsed) GCtime0.64s ( 0.31s elapsed) EXIT time0.00s ( 0.00s elapsed) Total time7.28s ( 9.66s elapsed) %GC time 8.8% (3.2% elapsed) Alloc rate416,628,033 bytes per MUT second Productivity 91.0% of total user, 68.6% of total elapsed We see that our one spark is pruned. Why? And another question. I compiled it also with -O: C:\ghc --make -threaded Monte.hs -O -fforce-recomp [1 of 1] Compiling Main ( Monte.hs, Monte.o ) Linking Monte.exe ... C:\monte +RTS -N2 -s monte +RTS -N2 -s pi 1 n: 100 3.148096 2,642,947,868 bytes allocated in the heap 1,801,952 bytes copied during GC 5,864 bytes maximum residency (1 sample(s)) 18,876 bytes maximum slop 2 MB total memory in use (0 MB lost due to fragmentation) Generation 0: 5077 collections, 5076 parallel, 0.08s, 0.05s elapsed Generation 1: 1 collections, 1 parallel, 0.00s, 0.00s elapsed Parallel GC work balance: 1.00 (445245 / 444651, ideal 2) MUT time (elapsed) GC time (elapsed) Task 0 (worker) :3.94s( 14.02s) 0.00s( 0.00s) Task 1 (worker) :0.00s( 14.02s) 0.00s( 0.00s) Task 2 (worker) :5.61s( 14.03s) 0.08s( 0.05s) Task 3 (worker) :0.00s( 14.05s) 0.00s( 0.00s) SPARKS: 1 (0 converted, 0 pruned) INIT time0.02s ( 0.02s elapsed) MUT time9.55s ( 14.03s elapsed) GCtime0.08s ( 0.05s elapsed) EXIT time0.00s ( 0.00s elapsed) Total time9.64s ( 14.09s elapsed) %GC time 0.8% (0.3% elapsed) Alloc rate276,386,705 bytes per MUT second Productivity 99.0% of total user, 67.7% of total elapsed We see, that with -O, 2 worker threads were doing some job, but overall performance is not better. From one spark, zero - converted, zero - pruned. Is it a bug? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Performance of Knight's Tour
Hi! I'm learning Haskell, and now I'm trying to make framework for solving searching problems, such as Knight's Tour. For small boards it answers instantly. For 7x8 board - 23 seconds. For 8x8 board - more than 30 minutes (it hasn't finished yet). Where is the root of the evil? --program module Main where import Data.List import Data.Array.Unboxed import qualified Data.Array.IArray as IArr import Data.Ix data SResult = Good | GoodProcess | Process | Bad data SDPSearch a p r = SDPSearch (a - p - [a]) --expand (p - p) --update (a - p - SResult) --sort ([a] - r)--result runSDPSearch :: SDPSearch a c b - [a] - c - b runSDPSearch (SDPSearch e u s r) list p = r (rec list params) where params = iterate u p rec [] _ = [] rec (l:lp) pr@(n:np) = case s l n of Good- l : rec lp pr GoodProcess - l : (rec (e l n) np) ++ (rec lp pr) Process - (rec (e l n) np) ++ (rec lp pr) Bad - rec lp pr main = do (a, b) - (break (== ' ')) `fmap` getLine print (knightTour (read a) (read b)) knightTour :: Int - Int - UArray (Int, Int) Int knightTour a b = runSDPSearch (SDPSearch e u s r) [((1, 1), sArray)] 2 where size = a * b range = ((1, 1), (a, b)) sArray = listArray range (1 : (replicate (size - 1) 0)) allTurns :: Array (Int, Int) [(Int, Int)] allTurns = IArr.listArray range [turns x y | x - [1..a], y - [1..b]] where shifts = [(1, 2),(1, -2),(2, 1),(2, -1),(-1, 2),(-1, -2),(-2, 1),(-2, -1)] turns x y = [(x+i, y+j) | (i, j) - shifts, inRange range (x+i, y+j)] e ((x, y), arr) p = [(t, arr // [(t, p)]) | t - changes] where changes = [t | t - allTurns ! (x, y), arr ! t == 0] s el p | p == size = Good | otherwise = Process u = (+ 1) r l | not (null l) = snd (head l) | otherwise= error No solutions! ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Performance of Knight's Tour
2010/3/1 Daniel Fischer daniel.is.fisc...@web.de: In the algorithm. You investigate far too many dead ends. Since for larger boards, the number of dead ends increases fast, larger boards take much much longer. With one little change, I get ... For a reason I don't understand, if the second dimension is 60 and the first is 18, it takes much longer, ... The magic change: e ((x, y), arr) p = [(t, arr // [(t, p)]) | t - changes] where legit ps = [t | t - allTurns ! ps, arr!t == 0] changes = map snd $ sort [(length $ legit t, t) | t - allTurns ! (x, y), arr ! t == 0] investigate squares with fewer options first. Wow! Thanks you! By the way, I didn't notice the difference between (59, 59) and (60, 60) on my machine... ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Performance of Knight's Tour
2010/3/1 Daniel Fischer daniel.is.fisc...@web.de: Am Montag 01 März 2010 19:29:45 schrieb Artyom Kazak: 2010/3/1 Daniel Fischer daniel.is.fisc...@web.de: In the algorithm. You investigate far too many dead ends. Since for larger boards, the number of dead ends increases fast, larger boards take much much longer. With one little change, I get ... For a reason I don't understand, if the second dimension is 60 and the first is 18, it takes much longer, ... The magic change: e ((x, y), arr) p = [(t, arr // [(t, p)]) | t - changes] where legit ps = [t | t - allTurns ! ps, arr!t == 0] changes = map snd $ sort [(length $ legit t, t) | t - allTurns ! (x, y), arr ! t == 0] investigate squares with fewer options first. Wow! Thanks you! By the way, I didn't notice the difference between (59, 59) and (60, 60) on my machine... Strangely, $ echo 62 59 | time ./knights /dev/null 0.10user 0.08system 0:00.17elapsed 101%CPU $ echo 65 59 | time ./knights /dev/null 0.08user 0.07system 0:00.17elapsed 96%CPU , so it's a thing of the second dimension predominantly (the size plays a small role, too). As I said, I don't understand it, but looking at the allocation figures: 70*59: 97,970,072 bytes allocated in the heap 18*60: 12,230,296 bytes allocated in the heap 19*60: 2,374,148,320 bytes allocated in the heap 19*61: 13,139,688 bytes allocated in the heap 60*61: 71,771,324 bytes allocated in the heap 61*61: 72,965,428 bytes allocated in the heap it seems that something is kicked out of the registers when the second dimension is 60 and the first 18. Very strange. Maybe we were compiling with different options? I compiled with -O2 -fvia-C -optc-O3. ... Oh, I know! I slightly changed the code. import Data.Ord e ((x, y), arr) p = [(t, arr // [(t, p)]) | t - changes] where legit ps = [t | t - allTurns ! ps, arr ! t == 0] changes = sortOn (length . legit) (legit (x, y)) sortOn = sortBy . comparing My version gives answer for 60, 60 in one second. But if both dimensions are 60, it won't finish. Yes, very strange. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GHC RTS question
2010/2/24 Brandon S. Allbery KF8NH allb...@ece.cmu.edu:
On Feb 22, 2010, at 03:36 , Roman Cheplyaka wrote:
* Anthony Cowley acow...@seas.upenn.edu [2010-02-21 14:15:00-0500]
#! /usr/bin/env bash
./prog --RTS $*
./prog --RTS $@
Otherwise it will work wrong if arguments contain quoted field
separators (e.g. spaces).
#! /bin/sh
./prog --RTS ${1+$@}
The longer specification above should work with whatever /bin/sh is around,
whether it's Solaris /sbin/sh, FreeBSD's sh, general Linux bash,
Debian/Ubuntu dash, etc.
And with Windows, of course :) Haskell is cross-platform, isn't it?
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[Haskell-cafe] GHC RTS question
Hello everybody! I want to write a little program, that will receive a string as command-line argument and write it in the file. But if this string contains '+RTS', GHC runtime won't pass the rest of the string to my program. What can I do to avoid this? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GHC RTS question
Enclose it in double quotes (perhaps single quotes would also work) No, I want my program to work the same way as UNIX echo does. Without any double quotes. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GHC RTS question
2010/2/21 Daniel Fischer daniel.is.fisc...@web.de: Am Sonntag 21 Februar 2010 18:20:43 schrieb Artyom Kazak: Enclose it in double quotes (perhaps single quotes would also work) No, I want my program to work the same way as UNIX echo does. Without any double quotes. Okay, what about If you absolutely positively want all the rest of the options in a command line to go to the program (and not the RTS), use a ––RTS. $ ./prog +RTS --RTS +RTS ? (BTW, enclosing in quotes doesn't work anyway if the argument consists *only* of +RTS, same as with echo, echo -e doesn't output '-e' either). So, if I type ./prog +RTS --RTS +RTS, the output will be +RTS. But I want the output to be equal to the input IN ALL CASES, without any quotes, additional options, etc. I want all the command line to go to my program. How can I do it? (The only way I know now - hacking the GHC. If there are no other ways, I'll do it.) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Mysterious factorial
Why fact2 is quicker than fact?! fact2 :: Integer - Integer fact2 x = f x y where f n e | n 2 = 1 | e == 0 = n * (n - 1) | e 0 = (f n (e `div` 2)) * (f (n - (e * 2)) (e `div` 2)) y = 2 ^ (truncate (log (fromInteger x) / log 2)) fact :: Integer - Integer fact 1 = 1 fact n = n * fact (n - 1) I tried to write tail-recursive fact, fact as product [1..n] - fact2 is quicker! fact2 100 == fact 100 - I tested. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
