Re: [Haskell-cafe] function arithmetic?
On 08/31/2013 09:27 PM, Charlie Paul wrote: I believe that this is what you want: http://www.haskell.org/haskellwiki/Num_instance_for_functions On Sat, Aug 31, 2013 at 10:01 PM, Christopher Howard christopher.how...@frigidcode.com wrote: The author seemed to be subtly mocking the idea. It seemed to be suggesting that a Num instance for functions would imply the need for constant number functions, which leads to difficulties. But I don't see why one would have to take it that far. In any case, I just tried the NumInstances package from Hackage and it seems to work great. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] function arithmetic?
Hi. I was just curious about something. In one of my math textbooks I see expressions like this f + g or (f + g)(a) where f and g are functions. What is meant is f(a) + g(a) Is there a way in Haskell you can make use of syntax like that (i.e., expressions like f + g and f * g to create a new function), perhaps by loading a module or something? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] continuations and monads
Q: Are the continuations in Scheme related to the monads from Haskell? If so, could someone elaborate on that? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] memoization
When I previously asked about memoization, I got the impression that memoization is not something that just happens magically in Haskell. Yet, on a Haskell wiki page about Memoization http://www.haskell.org/haskellwiki/Memoization#Memoization_with_recursion, an example given is memoized_fib :: Int - Integer memoized_fib = (map fib [0 ..] !!) where fib 0 = 0 fib 1 = 1 fib n = memoized_fib (n-2) + memoized_fib (n-1) I guess this works because, for example, I tried memoized_fib 1 and the interpreter took three or four seconds to calculate. But every subsequent call to memoized_fib 1 returns instantaneously (as does memoized_fib 10001). Could someone explain the technical details of why this works? Why is map fib [0 ..] not recalculated every time I call memoized_fib? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] memoization
On 07/21/2013 11:19 PM, KC wrote: Have you tried the compiler? No. Would that work differently some how? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] memoization
On 07/21/2013 11:52 PM, Chris Wong wrote: [.. snipped ..] A binding is memoized if, ignoring everything after the equals sign, it looks like a constant. In other words, these are memoized: x = 2 Just x = blah (x, y) = blah f = \x - x + 1 -- f = ... and these are not: f x = x + 1 f (Just x, y) = x + y If you remove the right-hand side of memoized_fib, you get: memoized_fib = ... This looks like a constant. So the value (map fib [0..] !!) is memoized. If you change that line to memoized_fib x = map fib [0..] !! x GHC no longer memoizes it, and it runs much more slowly. -- Chris Wong, fixpoint conjurer e: lambda.fa...@gmail.com w: http://lfairy.github.io/ Thanks. That's very helpful to know. Yet, it seems rather strange and arbitrary that f x = ... and f = \x - ... would be treated in such a dramatically different manner. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] memoization
On 07/22/2013 06:16 AM, Andreas Abel wrote: On 22.07.2013 09:52, Chris Wong wrote: True, but the essential thing to be memoized is not memoized_fib, which is a function, but the subexpression map fib [0..] which is an infinite list, i.e., a value. The rule must be like in let x = e if e is purely applicative, then its subexpressions are memoized. For instance, the following is also not memoizing: fib3 :: Int - Integer fib3 = \ x - map fib [0 ..] !! x where fib 0 = 0 fib 1 = 1 fib n = fib3 (n-2) + fib3 (n-1) In general, I would not trust such compiler magic, but just let-bind anything I want memoized myself: memoized_fib :: Int - Integer memoized_fib x = fibs !! x where fibs = map fib [0..] -- lazily computed infinite list fib 0 = 0 fib 1 = 1 fib n = memoized_fib (n-2) + memoized_fib (n-1) The eta-expansions do not matter. Cheers, Andreas Is this behavior codified somewhere? (I can't seem to find it in the GHC user guide.) The memoize package from hackage, interestingly enough, states that [Our memoization technique] relies on implementation assumptions that, while not guaranteed by the semantics of Haskell, appear to be true. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] memoization
On 07/22/2013 03:41 PM, David Thomas wrote: I, for one, would love to have a compiler do (a) based on (b), my specification of (c), and the ability to pin particular things... The reason it is a big deal to me is it sometimes the more natural-looking (read, declarative) way of writing a function is only reasonably efficient if certain parts are memoized. Otherwise I end up having to pass around extra arguments or data structures representing the data I don't want to be recalculated. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] partially indeterminate?
Hi. For learning, I was doing the phone words problem, where a function translates the digits of a phone number into all possible words. I am trying to connect this idea to the idea of list comprehensions / list monads (sort of the same thing, yes?) I know it is easy to do this: w = do two - ABC three - DEF four - GHI -- and the other digits [[two, three, two, four]] -- for example But what if you don't know in advance what the digits will be? I'm not sure how to insert that deterministic component into this idea. So far, I have a framework like so: p dx = do undefined where m = map (\d - case d of 2 - ABC 3 - DEF 4 - GHI 5 - JKL 6 - MNO 7 - PRS 8 - TUV 9 - WXY otherwise - show d) dx I would appreciate any guidance. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Roman Numeral Problem
Hi. I am working on some practice programming problems, and one is the Roman numeral problem: write a program that converts Roman numerals into their (arabic) numeral equivalent. I imagine I could hack something together, but I was trying to think about the problem a bit more deeply. I don't know much about parsing, but I was wondering if this problem matched up with some kind of parsing or grammar or other generic approach to thinking about the problem. (I once read something about Context Free Grammars, which was rather interesting.) I can do more of my own research if I can get some initial guidance. -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Efficiency/Evaluation Question
I'm working through some beginner-level keyboard problems I found at users.csc.calpoly.edu. One problem is the Saddle Points problem: quote: Write a program to search for the saddle points in a 5 by 5 array of integers. A saddle point is a cell whose value is greater than or equal to any in its row, and less than or equal to any in its column. There may be more than one saddle point in the array. Print out the coordinates of any saddle points your program finds. Print out No saddle points if there are none. Let's say I use a simple list grid like so: code: array = Grid 5 [ [1,5,3,6,4] , [8,2,6,3,8] , [3,8,7,2,9] , [0,3,7,1,2] , [7,2,7,4,5] ] data Grid = Grid Int [[Int]] And let's say I take a brute force approach, moving through each cell, checking to see if it is the greatest in its row and the least in its column. And say I have functions like so for getting rows and columns: code: row (Grid s l) n = if (n = s) then [] else l !! n col g@(Grid s l) n = if (n = s) then [] else col_ g n 0 where col_ (Grid s l) n i = if (i = s) then [] else (head l !! n) : col_ (Grid s (tail l)) n (i + 1) My question: With the way Haskell works (thunks, lazy evaluation, and all that mystery), is it actually worth the trouble of /precalculating/ the maximum row values and minimum column values, to compare cell values against? Or will, for example, something like (smallest_list_value (col array 1)) definitely only evaluate once? -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Efficiency/Evaluation Question
On 06/15/2013 04:39 PM, Tommy Thorn wrote:
There's not enough context to answer the specific question,
but lazy evaluation isn't magic and the answer is probably no.
Tommy
Perhaps to simplify the question somewhat with a simpler example.
Suppose you have
code:
let f x = if (x 4) then f 0 else (sin x + 2 * cos x) : f (x + 1)
After calculating at x={0,1,2,3}, and the cycle repeats, are sin, cos,
etc. calculated anymore?
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Re: [Haskell-cafe] Efficiency/Evaluation Question
On 06/15/2013 05:02 PM, Christopher Howard wrote:
On 06/15/2013 04:39 PM, Tommy Thorn wrote:
Perhaps to simplify the question somewhat with a simpler example.
Suppose you have
code:
let f x = if (x 4) then f 0 else (sin x + 2 * cos x) : f (x + 1)
After calculating at x={0,1,2,3}, and the cycle repeats, are sin, cos,
etc. calculated anymore?
That might have been ambiguous. What I meant was:
code:
let f x = if (x 4) then f 0 else (sin x + 2 * cos x) : f (x + 1)
If I calculate (f 0), and the cycle repeats after four values, are sin,
cos, etc. calculated anymore?
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Re: [Haskell-cafe] Simplest way to learn FRP through use
On 05/31/2013 07:47 PM, Tikhon Jelvis wrote: My favorite mini app is John Conway's game of life. I implemented a version with reactive banana and found it perfect for learning the ideas. I have a simple version of the code up on GitHub if you ever want a nice example to read. I tried to make the code neat rather than worrying about performance or features. Would you be willing to give a URL for that? (To save posterity from the trouble of putting your name in a GitHub search box.) -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Simplest way to learn FRP through use
I want to learn FRP but am having trouble wading through all the theory about how FRP is implemented and how it /could/ be used for various applications. What is the simplest, easiest-to-learn module or system allowing you to quickly make something interesting (if not very impressive) in an FRP style? Say, a simple simulation of some physical phenomena outputting its state to the terminal; or an object moving on the screen; or some other toy application that I could create and play with. -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] rip in the class-abstraction continuum
On 05/19/2013 10:10 PM, Tillmann Rendel wrote:
This is not easily possible. If you could just put the constraint into
the instance, there would be a problem when youc all toXy in a
polymorphic context, where a is not known. Example:
class XyConv a where
toXy :: a b - [Xy b]
shouldBeFine :: XyConv a = a String - [Xy String]
shouldBeFine = toXy
This code compiles fine, because the type of shouldBeFine is an instance
of the type of toXy. The type checker figures out that here, b needs to
be String, and since there is no class constraint visible anywhere that
suggests a problem with b = String, the code is accepted.
The correctness of this reasoning relies on the fact that whatever
instances you add in other parts of your program, they can never
constrain b so that it cannot be String anymore. Such an instance would
invalidate the above program, but that would be unfair: How would the
type checker have known in advance whether or not you'll eventually
write this constraining instance.
So this is why in Haskell, the type of a method in an instance
declaration has to be as general as the declared type of that method in
the corresponding class declaration.
Now, there is a way out using some of the more recent additions to the
language: You can declare, in the class, that each instance can choose
its own constraints for b. This is possible by combining constraint
kinds and associated type families.
{-# LANGUAGE ConstraintKinds, TypeFamilies #-}
import GHC.Exts
The idea is to add a constraint type to the class declaration:
class XyConv a where
type C a :: * - Constraint
toXy :: C a b = a b - [Xy b]
Now it is clear to the type checker that calling toXy requires that b
satisfies a constraint that is only known when a is known, so the
following is not accepted.
noLongerAccepted :: XyConv a = a String - [Xy String]
noLongerAccepted = toXy
The type checker complains that it cannot deduce an instance of (C a
[Char]) from (XyConv a). If you want to write this function, you have to
explicitly state that the caller has to provide the (C a String)
instance, whatever (C a) will be:
haveToWriteThis :: (XyConv a, C a String) = a String - [Xy String]
haveToWriteThis = toXy
So with associated type families and constraint kinds, the class
declaration can explicitly say that instances can require constraints.
The type checker will then be aware of it, and require appropriate
instances of as-yet-unknown classes to be available. I think this is
extremely cool and powerful, but maybe more often than not, we don't
actually need this power, and can provide a less generic but much
simpler API.
Tillmann
Thank you for the quick and thorough response. To be honest though, I
had some difficulty following your explanation of the constraints
problem. I had an even more difficult time when I tried to read up on
what Type Families are -- ended up at some wiki page trying to explain
Type Families by illustrating them with Generic Finite Maps (a.k.a.,
Generic Prefix Trees). The rough equivalent of learning German through a
Latin-German dictionary. :|
Anyway, I played around with my code some more - and it seems like what
I am trying to do can be done with multi-parameter type classes:
code:
{-# LANGUAGE MultiParamTypeClasses, FlexibleInstances #-}
class XyConv a b where
toXy :: a b - [Xy b]
instance (Integral a, Floating b) = XyConv (CircAppr a) b where
toXy (CircAppr divns ang rad) =
let dAng = 2 * pi / (fromIntegral divns) in
let angles = map ((+ ang) . (* dAng) . fromIntegral) [0..divns] in
map (\a - am2xy a rad) angles
Seems to work okay:
code:
h toXy (CircAppr 4 0.0 1.0)
[Xy 1.0 0.0,Xy 6.123233995736766e-17 1.0,Xy (-1.0)
1.2246467991473532e-16,Xy (-1.8369701987210297e-16) (-1.0),Xy 1.0
(-2.4492935982947064e-16)]
h :t toXy (CircAppr 4 0.0 1.0)
toXy (CircAppr 4 0.0 1.0) :: Floating b = [Xy b]
Is there anything bad about this approach?
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[Haskell-cafe] rip in the class-abstraction continuum
Hi. I won't pretend to be an advanced Haskell programmer. However, I have a strong interest in abstraction, and I have been playing around with programming as abstractly as possible. Naturally, I find classes to be quite attractive and useful. However, something is bothering me. Lately I keep running into this situation where I have to cut across abstraction layers in order to make the code work. More specifically, I keep finding that I have to add constraints to a class definition, because eventually I find some instance of that class which needs those constraints to compile. For example, I wanted to create a class which represents all things that can be converted into X,Y coordinates. Naturally, I would like to do something like this: code: class XyConv a where toXy :: a b - [Xy b] This leaves me free in the future to use any number type conceivable in the Xy coordinates - Floating or Integral types, or whatever. (Doesn't even have to be numbers, actually!) However the first instance I create, requires me to use operators in the function definition which require at least a Floating type. (The error will say Fractional, but there are other components that also require Floating.) code: data CircAppr a b = CircAppr a b b -- number of points, rotation angle, radius deriving (Show) instance Integral a = XyConv (CircAppr a) where toXy (CircAppr divns ang rad) = let dAng = 2 * pi / (fromIntegral divns) in let angles = map ((+ ang) . (* dAng) . fromIntegral) [0..divns] in map (\a - am2xy a rad) angles This gives me the error code: Could not deduce (Fractional b) arising from a use of `/' from the context (Integral a) bound by the instance declaration at /scratch/cmhoward/pulse-spin/pulse-spin.hs:51:10-42 Possible fix: add (Fractional b) to the context of the type signature for toXy :: CircAppr a b - [Xy b] or the instance declaration In the expression: 2 * pi / (fromIntegral divns) In an equation for `dAng': dAng = 2 * pi / (fromIntegral divns) In the expression: let dAng = 2 * pi / (fromIntegral divns) in let angles = map ((+ ang) . (* dAng) . fromIntegral) [0 .. divns] in map (\ a - am2xy a rad) angles I can get a quick fix by adding Floating to the context of the /class/ definition: code: class XyConv a where toXy :: Floating b = a b - [Xy b] But what I really want is to put Floating in the context of the /instance/ declaration. But I don't know how to do that syntactically. -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] fromIntegral not enough?
This is probably a haskell-beginners sort of question, but I usually get about 4x as many responses from cafe, about 10x as fast. I have code like so: code: data Xy a = Xy a a class Coord2 a where coords2 :: Fractional b = a b - Xy b data CircAppr a b = CircAppr a b b -- number of points, rotation angle, radius deriving (Show) instance Integral a = Coord2 (CircAppr a) where coords2 (CircAppr divns ang rad) = let dAng = 2 * pi / (fromIntegral divns) in let angles = map (* dAng) [0..divns] in undefined -- To be coded... In the instance definition divns is an integral trying to divide a fractional. I hoped wrapping it in fromIntegral would coerce, but apparently not: quote: Could not deduce (Fractional a) arising from a use of `/' from the context (Integral a) bound by the instance declaration at /scratch/cmhoward/pulse-spin/pulse-spin.hs:34:10-42 or from (Fractional b) bound by the type signature for coords2 :: Fractional b = CircAppr a b - Xy b at /scratch/cmhoward/pulse-spin/pulse-spin.hs:(36,3)-(39,15) Possible fix: add (Fractional a) to the context of the type signature for coords2 :: Fractional b = CircAppr a b - Xy b or the instance declaration In the expression: 2 * pi / (fromIntegral divns) In an equation for `dAng': dAng = 2 * pi / (fromIntegral divns) In the expression: let dAng = 2 * pi / (fromIntegral divns) in let angles = map (* dAng) [0 .. divns] in undefined So, I'm wondering how I can do what I'm trying to do here, while still keeping my types as generic as possible. -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] fromIntegral not enough?
On 05/13/2013 02:53 PM, Tom Ellis wrote: On Mon, May 13, 2013 at 11:43:41PM +0100, Tom Ellis wrote: You probably want let angles = map ((* dAng) . fromInteger) [0..divns] in ... instead. Ah, that works. Thanks all. -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Flip around type parameters?
Hi. Does Haskell allow you to flip around type parameters somehow? I was playing around with toy code (still learning the fundamentals) and I came up with a class like this: code: class Rotatable2D a where rotate :: (Num b) = (a b) - b - (a b) It was easy to make an instance of a generic single-parameter type: code: data Angle a = Angle a deriving (Show) instance Rotatable2D Angle where rotate (Angle a) b = Angle (a + b) But let's say I have something a little more complicated: code: data CircAppr a b = CircAppr a a b -- radius, rotation angle, number of points I think I need something like so: instance Rotatable2D (\x - CircAppr x a) where rotate (CircAppr a b c) d = CircAppr a (b + d) c But I tried that and it isn't valid syntax. -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] GPGPU
Has anybody on the list been playing around with OpenCL at all? I'm just starting to look into it - need to get a newer Radeon card, I think - but I'm strongly interested in GPGPU programming. -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Cabal / cabal-install: special installation
Hi. This question dovetails off my previous thread. I described how I got ghc-7.6.3 installed from source onto an old RHEL5 machine. Naturally, I want to get cabal-install installed and start building great Hackage software. However, I have this quirk: I installed GHC to a special directory using ./configure --prefix=/specialdirectory/local. It is in my path, and works just fine. But when I try to build cabal-install, it claims it can't find Base, Cabal, and a few other things I know are installed. I know they are installed because I can see where they are installed and I can import stuff from them within GHCI. The result is the same whether I use the boot script, or whether I use runhaskell Setup configure (with or without a --prefix option). Is there another environment variable I need to set or something like that? (I need to emphasize that I do not want to install anything to $HOME, because my $HOME directory is shared across multiple systems.) -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Looking for portable Haskell or Haskell like language
On 05/01/2013 12:21 AM, Gabor Greif wrote: Am 27. April 2013 um 07:21 schrieb Christopher Howard christopher.how...@frigidcode.com: I can feel your pain... Here is a blog post I have written some time ago http://heisenbug.blogspot.de/2011/09/ghc-704-on-centos.html about how to bridge the gap. This was actually a RHEL5 system, but did not want to admit it :-) My writeup may be useful to you. Cheers, Gabor For posterity's sake: I actually got this figured out already. First, I downloaded the binary version of GHC 6.8.3 and installed it without issues. Then I used it to build the sources of GHC 6.10.4 and install them. Then I used 6.10.4 to build and install 6.12.3. Then 7.0.4, then 7.2.2, then 7.4.2, and finally 7.6.3. Had no problems doing it that way, except for the optimization flags issue in the 7.* series which I mentioned in my other thread. That was easily fixed by setting the build.mk to the quick build profile. -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ghc-7 -fPIC error
Hey guys, this probably isn't the official GHC mailing list, but I've been trying to build and install a new GHC on an old RHEL5 system, as mentioned in my previous Cafe thread. I was able to make some good headway: I installed a ghc-6.8 binary, and then used that to build ghc-6.10 source, and then used that to build ghc-6.12 source. The idea is to keep going until I get to ghc-7.6. However, when I get to 7.0, my builds all eventually die with this error: quote: /usr/bin/ld: rts/dist/build/RtsStartup.dyn_o: relocation R_X86_64_PC32 against `StgRun' can not be used when making a shared object; recompile with -fPIC /usr/bin/ld: final link failed: Bad value collect2: ld returned 1 exit status After this failed the first time, I tried adding -fPIC to SRC_HC_OPTS, GhcStage1HcOpts, and so forth in build.mk. But ultimately I get the same error. I tried skipping a version and building ghc-7.2 instead, but the same error pops up. -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Looking for portable Haskell or Haskell like language
On 04/27/2013 08:36 AM, Jerzy Karczmarczuk wrote: Christopher Howard: Is the portability which worries you, or the age of your system? Actually getting a successful build and installation would be great. Also, there are multiple systems I work with, both of which have ancient software, but unfortunately are not the same configuration. I often find software that builds on one, but not the other. Hugs (and Gofer before) are simply sufficiently old... I used them on Red Hat in one of my previous lives. Do you really need to compile your system from sources? I guess not, if I can get one to install successfully to a local (non-root) user account. As mentioned, GHC Linux binaries failed me here, because apparently the gnu libc version is too old. With most software, I generally have had more success installing from source than trying to work with pre-built. There are binaries everywhere. If you want a *simpler* language, perhaps try Miranda? Also a quite ancient language... Or, perhaps a newer one, in some aspects simpler than Haskell (but far from any simplicity): Clean. To be clearer, I do not really want any language other than Haskell. I just imagined that a simpler language might have a simpler and more portable compiler. Perhaps it might help to know what do you need it for... In brief, I have access to some large super computer systems. Sadly, nobody in my academic or work circles seems to have the slightest interest in applying functional languages to parallel computing problems (C and Fortran seem to be the languages of choice.) So, I've been poking around with some functional languages, trying to see what I could get installed (without any admin assistance whatsoever) and how I might be able to use them with the MPI or even GPGPU infrastructure we have. But I keep running into problems, because the software infrastructure is quite ancient (for compatibility purposes, I'm told), or there are other mysterious configuration issues. -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Looking for portable Haskell or Haskell like language
Hi. I've got this work situation where I've got to do all my work on /ancient/ RHEL5 systems, with funky software configurations, and no root privileges. I wanted to install GHC in my local account, but the gnu libc version is so old (2.5!) that I can't even get the binary packages to install. I've had success installing some other simple functional languages (like CLISP) on these same systems, so I was wondering if there was perhaps another language very similar to Haskell (but presumably simpler) with a super portable compiler easily built from source, which I could try. I'll admit -- I haven't tried the HUGS compiler for Haskell. The quick description didn't make it sound much more portable than GHC, but I guess I could try it if I heard some good reasons to think it would be more portable. -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Monad fold
So, I'm doing something like this foldl (=) someA list :: Monad m = m a where list :: Monad m = [a - m a], someA :: Monad m = m a Is there a more concise way to write this? I don't think foldM is what I want -- or is it? -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Fwd: [Haskell-beginners] Monad instances and type synonyms
I asked this question in Haskell-beginners, but I haven't heard anything yet, so I'm forwarding to Cafe. Original Message Subject: [Haskell-beginners] Monad instances and type synonyms Date: Sat, 13 Apr 2013 17:03:57 -0800 From: Christopher Howard christopher.how...@frigidcode.com Reply-To: The Haskell-Beginners Mailing List - Discussion of primarily beginner-level topics related to Haskell beginn...@haskell.org To: Haskell Beginners beginn...@haskell.org I am playing around with some trivial code (for learning purposes) I wanted to take code: -- SaleVariables a concrete type defined early -- `Adjustment' represents adjustment in a price calculation -- Allows functions of type (a - Adjustment a) to be composed -- with an appropriate composition function type Adjustment a = SaleVariables - a And put it into code: instance Monad Adjustment where (=) = ... return = ... If I try this, I get code: Type synonym `Adjustment' should have 1 argument, but has been given none In the instance declaration for `Monad Adjustment' But if I give an argument, then it doesn't compile either (it becomes a * kind). And I didn't want to make the type with a regular data declaration either, because then I have to give it a constructor, which doesn't fit with what I want the type to do. -- frigidcode.com ___ Beginners mailing list beginn...@haskell.org http://www.haskell.org/mailman/listinfo/beginners signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] exp implementation
On 04/11/2013 06:37 AM, Brandon Allbery wrote: On Thu, Apr 11, 2013 at 1:38 AM, Christopher Howard christopher.how...@frigidcode.com mailto:christopher.how...@frigidcode.com wrote: Hi. For my own learning, I wanted to see how the exp function is implemented in GHC. I have GHC 7.4.1 source code open, but I'm having trouble figuring out which file the actual function definition is in. I see expFloat(F# x) = F# (expFloat# x) expFloat# is likely a primop; good luck Primops aka primitive operations are generally implemented in the compiler backend as assembly language or Cmm code. Untangling that part of ghc makes my head swim. . -- brandon s allbery kf8nh sine nomine associates allber...@gmail.com mailto:allber...@gmail.com ballb...@sinenomine.net mailto:ballb...@sinenomine.net unix, openafs, kerberos, infrastructure, xmonadhttp://sinenomine.net I traced it down some more: I think it eventually goes into the compiler/nativeGen section where it is translated into the platform's native version of the function. On my platform, I think this is the expf function from math.h. (See EXP(3)). I find that to be interesting, because it means you could change the output of your programs by altering your standard library. But I guess there are a lot of things you could change by altering your standard library! -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] exp implementation
On 04/11/2013 07:12 AM, Christopher Howard wrote: On 04/11/2013 06:37 AM, Brandon Allbery wrote: I traced it down some more: I think it eventually goes into the compiler/nativeGen section where it is translated into the platform's native version of the function. On my platform, I think this is the expf function from math.h. (See EXP(3)). I find that to be interesting, because it means you could change the output of your programs by altering your standard library. But I guess there are a lot of things you could change by altering your standard library! ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe In glibc, it eventual comes down to this approximation, I think (from ./sysdeps/ieee754/flt-32/e_expf.c): code: /* Compute ex2 = 2^n e^(t/512+delta[t]). */ ex2_u.d = __exp_atable[tval+177]; ex2_u.ieee.exponent += (int) n; /* Approximate e^(dx+delta) - 1, using a second-degree polynomial, with maximum error in [-2^-10-2^-28,2^-10+2^-28] less than 5e-11. */ x22 = (0.500496709180453 * dx + 1.001192102037084) * dx + delta; /* ... snip ... */ result = x22 * ex2_u.d + ex2_u.d; -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] exp implementation
Hi. For my own learning, I wanted to see how the exp function is implemented in GHC. I have GHC 7.4.1 source code open, but I'm having trouble figuring out which file the actual function definition is in. I see expFloat(F# x) = F# (expFloat# x) in libraries/base/GHC/Float.lhs. -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] nice pattern from simple converging series
I made a nice little pattern from just a few lines of Haskell (mostly code comments) using gloss. It is very kindergarten in terms of mathematical art, but the idea was to illustrate that in a pretty short amount of time, and a small amount code, you could easily translate simple math concepts into geometry on your screen. http://frigidcode.com/code/haskell-series-circles/ -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] translating recursively defined sequence
Hi. My Haskell is (sadly) getting a bit rusty. I was wondering what would be the most straightforward and easily followed procedure for translating a recursively defined sequence into a Haskell function. For example, this one from a homework assignment. quote: a_1 = 10 a_(k+1) = (1/5) * (a_k)**2 (The underscore is meant to represent subscripting what follows it.) -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] translating recursively defined sequence
On 03/04/2013 08:36 PM, Bob Ippolito wrote: I suppose it depends on your definition of straightforward but you can use the iterate function from Data.List to quickly define sequences like this. a = iterate (\x - (1/5) * (x**2)) 10 On Mon, Mar 4, 2013 at 9:19 PM, Christopher Howard christopher.how...@frigidcode.com mailto:christopher.how...@frigidcode.com wrote: Hi. My Haskell is (sadly) getting a bit rusty. I was wondering what would be the most straightforward and easily followed procedure for translating a recursively defined sequence into a Haskell function. For example, this one from a homework assignment. quote: a_1 = 10 a_(k+1) = (1/5) * (a_k)**2 (The underscore is meant to represent subscripting what follows it.) -- frigidcode.com http://frigidcode.com Very cool! Thanks! -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] derivatives and integrals
Hi. The scope of this question is likely bigger that Haskell, but this seems like the right crowd to ask. I'm in Calc II right now, and I'm looking for a FOSS desktop application (I use Gnu/Linux) to replace the functionality of my TI-98 in finding derivatives and integrals. (It's very convenient for double checking my own solutions.) I've heard of some software like Octave, but the manuals are usually very large, and I'm not sure what is the best one to start with. I was wondering if there is anyone on this list who uses free software to do that sort of simpler Calc stuff, and what it is that they use. -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Where is the convergence point between Category Theory and Haskell?
On 01/13/2013 03:15 AM, Alfredo Di Napoli wrote: Morning Cafe, I'm planning to do a series of write-ups about Category Theory, to publish them on the company's blog I'm currently employed. I'm not a CT expert, but since the best way to learn something is to explain it to others, I want to take a shot :) In my mind I will structure the posts following Awodey's book, but I'm wondering how can I make my posts a little more real world. I always read about the Hask category, which seems to be the bootstrap of the whole logic behind Haskell. Can you please give my materials/papers/links/blogs to the Hask category and briefly explain me how it relates to Category Theory and Haskell itself? I hope my question is clear enough, in case is not, I'll restate :P Cheers, A. You want to give us the link to that blog? If you can keep your explanations reasonably illustrative and easy to understand, you'll get a regular reader out of me. -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ln, e
Hi. Are natural log and Euler's constant defined somewhere in base, or a convenience math module somewhere? I'm having trouble finding them with hayoo or system documentation. -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Proving programs
I'm working through a video lecture describing how to prove programs correct, by first translating the program into a control flow representation and then using propositional logic. In the control flow section, the speaker described how the program should be understood in terms of an input vector (X, the inputs to the program), a program vector (Y, the storage variables), and an output vector (Z, the outputs of the program), with X mapping into Y, Y being affected by execution, and X and Y mapping into Z. However, only part way into the video, two practical questions come to mind: 1. Does this approach need to be adjusted for a functional language, in which computation is (at least idealistically) distinct from control flow? 2. How do we approach this for programs that have an input loop (or recursion)? E.g., I have an application that reads one line for stdin, modifies said line, outputs to stdout, and repeats this process until EOF? Should I be thinking of every iteration as a separate program? -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] monoid pair of monoids?
On 12/20/2012 08:54 PM, Daniel Feltey wrote: You were only missing the restriction that both types a and b must be instances of Monoid in order to make Socket a b into an instance of Monoid. Dan Feltey Thank you for your help. An additional question, if I might: For the sake of elegance and simplicity, I modified the class and instances to avoid the tuple aspect: code: data Socket2 a b = Socket2 a b deriving (Show) instance (Monoid a, Monoid b) = Monoid (Socket2 a b) where mempty = Socket2 mempty mempty Socket2 a b `mappend` Socket2 w x = Socket2 (a `mappend` w) (b `mappend` x) Of course, I thought it would be likely I would want other classes and instances with additional numbers of types: code: data Socket3 a b c = Socket3 a b c deriving (Show) instance (Monoid a, Monoid b, Monoid c) = Monoid (Socket3 a b c) where mempty = Socket3 mempty mempty mempty Socket3 a b c `mappend` Socket3 w x y = Socket3 (a `mappend` w) (b `mappend` x) (c `mappend` y) data Socket4 a b c d = Socket4 a b c d deriving (Show) instance (Monoid a, Monoid b, Monoid c, Monoid d) = Monoid (Socket4 a b c d) where mempty = Socket4 mempty mempty mempty mempty Socket4 a b c d `mappend` Socket4 w x y z = Socket4 (a `mappend` w) (b `mappend` x) (c `mappend` y) (d `mappend` z) data Socket 5 a b c d e... et cetera Seeing as the pattern here is so rigid and obvious, I was wondering: is it possible to abstract this even more? So I could, for instance, just specify that I want a Socket with 8 types, and poof, it would be there? Or is this as meta as we get? (I.e., without going to something like Template Haskell.) -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Layer on a layer of record syntax in the type synonym?
Using a simple type I gave earlier from my monadic type question...
code:
data Socket3 a b c = Socket3 a b c
deriving (Show)
Is it possible somehow to layer on record syntax onto a synonym of the type?
The idea would be something like this...
code:
type SpaceShip =
Socket3 { engine :: Last Engine
, hull :: Last Hull
, guns :: [Guns]
}
...purely for the convenience. But this doesn't seem to work with type
as it assumes you are referring to already made constructors, and
evidently newtype only allows use of a single record. I could wrap it
in a normal data declaration but that would add an extra layer of
complexity I think.
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Re: [Haskell-cafe] Layer on a layer of record syntax in the type synonym?
On 12/21/2012 04:52 AM, Daniel Trstenjak wrote:
Why having a Socket3 in the first place, what's the point of it?
The idea was to have some generic structures (Sockets) which were
already instanced into the Monoids-within-Monoids abstraction, yet could
still be made concrete into anything more specific.
So, I have...
code:
data Socket3 a b c = Socket3 a b c
deriving (Show)
instance (Monoid a, Monoid b, Monoid c) = Monoid (Socket3 a b c) where
mempty = Socket3 mempty mempty mempty
Socket3 a b c `mappend` Socket3 w x y =
Socket3 (a w) (b x) (c y)
nullSocket3 :: (Monoid a, Monoid b, Monoid c) = Socket3 a b c
nullSocket3 = Socket3 mempty mempty mempty
...which allows me to have...
code:
type ShipSys = Socket3 (Last Engine) (Last RotThruster) [LinThruster]
nullShipSys :: ShipSys
nullShipSys = nullSocket3
setEngineSocket (Socket3 a b c) x = Socket3 x b c
engineSys :: Engine - ShipSys
engineSys a = setEngineSocket nullShipSys (Last (Just a))
mk1Engine = engineSys (Engine 100 1 Mark I)
-- etc.
And so, with each individual component being wrapped as a generic
ShipSys (ship system), I can make a complete system simply by composition:
code:
h :t mk1Engine
mk1Engine :: ShipSys
h :t stdRearThruster
stdRearThruster :: ShipSys
h :t stdFrontThruster
stdFrontThruster :: ShipSys
h :t stdRotThruster
stdRotThruster :: Power - ShipSys
h mk1Engine stdRearThruster stdFrontThruster stdRotThruster 10
Socket3 (Last {getLast = Just (Engine 100.0 1.0 Mark I)}) (Last
{getLast = Just (RotThruster 10.0)}) [LinThruster 3.1415927
1.0,LinThruster 0.0 0.5]
This seems to work well enough so far. But the issue I was concerned
about is: if I can't layer record syntax onto the type synonym, then I
have to rewrite a whole bunch of getters / setters each time I want to
add an attribute (e.g., requiring a switch from a Socket3 to a Socket4.)
If this is the case, then perhaps it would be better just to define the
ShipSys type directly, and directly instance it into the monoid abstraction.
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[Haskell-cafe] Categories (cont.)
I've perhaps been trying everyones patiences with my noobish CT questions, but if you'll bear with me a little longer: I happened to notice that there is in fact a Category class in Haskell base, in Control.Category: quote: class Category cat where A class for categories. id and (.) must form a monoid. Methods id :: cat a a the identity morphism (.) :: cat b c - cat a b - cat a c morphism composition However, the documentation lists only two instances of Category, functions (-) and Kleisli Monad. For instruction purposes, could someone show me an example or two of how to make instances of this class, perhaps for a few of the common types? My initial thoughts were something like so: code: instance Category Integer where id = 1 (.) = (*) -- and instance Category [a] where id = [] (.) = (++) --- But these lead to kind mis-matches. -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Categories (cont.)
On 12/20/2012 03:59 AM, wren ng thornton wrote: On 12/20/12 6:42 AM, Christopher Howard wrote: As mentioned in my other email (just posted) the kind mismatch is because categories are actually monoid-oids[1] not monoids. That is: class Monoid (a :: *) where mempty :: a mappend :: a - a - a class Category (a :: * - * - *) where id :: a i j (.) :: a j k - a i j - a i k Theoretically speaking, every monoid can be considered as a category with only one object. Since there's only one object/index, the types for id and (.) basically degenerate into the types for mempty and mappend. Notably, from this perspective, each of the elements of the carrier set of the monoid becomes a morphism in the category--- which some people find odd at first. In order to fake this theory in Haskell we can do: newtype MonoidCategory a i j = MC a instance Monoid a = Category (MonoidCategory a) where id = MC mempty MC f . MC g = MC (f `mappend` g) This is a fake because technically (MonoidCategory A X Y) is a different type than (MonoidCategory A P Q), but since the indices are phantom types, we (the programmers) know they're isomorphic. From the category theory side of things, we have K*K many copies of the monoid where K is the cardinality of the kind *. We can capture this isomorphism if we like: castMC :: MonoidCategory a i j - MonoidCategory a k l castMC (MC a) = MC a but Haskell won't automatically insert this coercion for us; we gotta do it manually. In more recent versions of GHC we can use data kinds in order to declare a kind like: MonoidCategory :: * - () - () - * which would then ensure that we can only talk about (MonoidCategory a () ()). Unfortunately, this would mean we can't use the Control.Category type class, since this kind is more restrictive than (* - * - * - *). But perhaps in the future that can be fixed by using kind polymorphism... [1] The -oid part just means the indexing. We don't use the term monoidoid because it's horrific, but we do use a bunch of similar terms like semigroupoid, groupoid, etc. Finally... I actually made some measurable progress, using these phantom types you mentioned: code: import Control.Category newtype Product i j = Product Integer deriving (Show) instance Category Product where id = Product 1 Product a . Product b = Product (a * b) I can do composition, illustrate identity, and illustrate associativity: code: h Product 5 Product 2 Product 10 h Control.Category.id (Product 3) Product 3 h Control.Category.id Product 3 Product 3 h Product 3 Control.Category.id Product 3 h (Product 2 Product 3) Product 5 Product 30 h Product 2 (Product 3 Product 5) Product 30 -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] monoid pair of monoids?
In my current pondering of the compose-able objects them, I was thinking it would be useful to have the follow abstractions: Monoids, which were themselves tuples of Monoids. The idea was something like so: code: import Data.Monoid instance Monoid (Socket2 a b) where mempty = Socket2 (mempty, mempty) Socket2 (a, b) `mappend` Socket2 (w, x) = Socket2 (a `mappend` w, b `mappend` x) data Socket2 a b = Socket2 (a, b) However, this does not compile because of errors like so: code: Sockets.hs:9:21: No instance for (Monoid a) arising from a use of `mempty' In the expression: mempty In the first argument of `Socket2', namely `(mempty, mempty)' In the expression: Socket2 (mempty, mempty) This makes sense, but I haven't figured out a way to rewrite this to make it work. One approach I tried was to encode Monoid constraints into the data declaration (which I heard was a bad idea) but this didn't work, even using forall. Also I tried to encode it into the instance declaration, but the compiler kept complaining about errant or illegal syntax. -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] category design approach for inconvenient concepts
On 12/17/2012 06:30 PM, Richard O'Keefe wrote: On 18/12/2012, at 3:45 PM, Christopher Howard wrote: It's basically the very old idea that an Abstract Data Type should be a nice algebra: things that look as though they ought to fit together should just work, and rearrangements of things ought not to change the semantics in surprising ways (i.e., Don't Be SQL). Categories contain two things: objects and arrows that connect objects. Some important things about arrows: - for any object x there must be an identity idx : x - x - any two compatible arrows must compose in one and only one way: f : x - y g : y - z = g . f : x - z - composition must be associative (f . g) . h = f . (g . h) when the arrows fit together. Of course for any category there is a dual category, so what I'm about to say doesn't really make sense, but there's sense in it somewhere: the things you are trying to hook together with your . operator seem to me more like objects than arrows, and it does not seem as if they hook together in one and only one way, so it's not so much _associativity_ being broken, as the idea of . being a composition in the first place. Since I received the two responses to my question, I've been trying to think deeply about this subject, and go back and understand the core ideas. I think the problem is that I really don't have a clear understanding of the basics of category theory, and even less clear idea of the connection to Haskell programming. I have been reading every link I can find, but I'm still finding the ideas of objects and especially morphisms to be quite vague. The original link I gave http://www.haskellforall.com/2012_08_01_archive.html purposely skipped over any discussion of objects, morphisms, domains, and codomains. The author stated, in his first example, that Haskell functions are a category, and proceeded to describe function composition. But here I am confused: If functions are a category, this would seem to imply (by the phrasing) that functions are the objects of the category. However, since we compose functions, and only morphisms are composed, it would follow that functions are actually morphisms. So, in the function category, are functions objects or morphisms? If they are morphisms, then what are the objects of the category? -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] efficient data structure: column with repeating values
Is there some good data type out there that basically provides a simple table, but with optimization for repeating values on one column? Something like: Data Table a b ...where it assumes that 'a' values will usually be unique, while 'b' values will usually be repeated from a small set? (But not needing to be fixed beforehand.) Like in... client | patron --- Bob| Tom Sarah | Tom Dick | Tom George | Harry Moe| Harry -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] category design approach for inconvenient concepts
On 12/18/2012 08:02 PM, Gershom Bazerman wrote: On 12/17/12 9:45 PM, Christopher Howard wrote: I don't think you're describing a Category in the sense of the Haskell Category typeclass. But that's ok! Just because some things are categories and are nice doesn't mean that we can't have other nice things that aren't necessarily categories. My first thought was something with multiple inputs and one output is often an Operad (http://en.wikipedia.org/wiki/Operad_theory) but associativity is still an issue. Also bear in mind that operads and categories are both *directional* whereas your notion of coupling doesn't seem to be (which has something to do with associativity failing, I'd imagine). I think the example I gave was pretty messed up anyway, because I was trying to compose objects rather than morphisms. But that directional aspect you mentioned does seem significant... so I guess my main question is how that things that are more complex (like a multi-directional system built from pluggable components) could be represented in the Categorical manner. I'm looking for the Grand Unifying Theory to follow, if you will; I really like the idea that all parts of my program could be cleanly and systematically composed from smaller pieces, in some beautiful design patter. Many of the problems in my practical programming, however, are not like the examples I have seen (nice pipes or unidirectional calculations) but rather complex fitting together of components. E.g., space ships are made up of guns + engines + shields + ammo. Different kinds of space ships may use the same kind of guns (reusable components) but some wont. Some will have many guns, some will have none. And such like issues. Soylemez seems to have answered this issue directly in his reply. Unfortunately, I didn't understand most of what he wrote. :| I also don't understand, e.g., what happens if I couple a thing with two connectors and one connector -- which connector from the first gets used, or are they interchangeable? The example I gave was hastily put together and not well thought out. I was Just trying to come up with something that would convey the general idea. But perhaps each component would have a list of connectors, and the first ones in the list would be used first. When a new component was created from other components, the new list would be taken from the leftover connectors (if any). In real world use I would probably have multiple types of connectors, but I haven't thought that far ahead. Going back even further, you've suggested a Fail to represent when the connectors don't match. Why not start with encoding connectors in types to begin with, so that it is a type error to not have matching connectors? Follow the logic of your idea, shape your types to match your representable states, and then see what algebraic structures naturally emerge. Cheers, Gershom Sounds good. Of course, I still haven't figured out what design pattern to fit said types into. :( -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] haskell-like scripting language
I gave Shelly a try. Pretty cool - using it for some of the scripts on my system. Has me wondering though: is anyone working on creating a actual Haskell-like scripting language and engine? Shelly is cool, as I said, but I imagine it would be more valuable to have another language that is actually separate from Haskell, with an interpreter that is more lightweight and changes much less frequently (than GHC). Something that could be nearly as portable as Bash or Perl. -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] category design approach for inconvenient concepts
Recently I read this article I happened across, about the categorical design pattern: http://www.haskellforall.com/2012/08/the-category-design-pattern.html Barely understood it, of course, but it was a rather intriguing concept. So now I'm looking at all my programming problems trying to make types that can be composed and that seem to fit the idea of a category. However, what I'm wondering about is ideas that can be composed but that don't seem to fit the idea of category, because they don't obey the associativity law. To give a specific example (pseudo code like, without any idea here of implementation or proper syntax): Say you created a type called Component (C for short), the idea being to compose Components out of other Components. Every C has zero or more connectors on it. Two Cs can be connected to form a new C using some kind of composition operator (say, .), provided there are enough connectors (one on each). Presumably you would need a Fail constructor of some kind to represent the situation when there is not enough connectors. Say you had a C (coupler) with two connectors, a C (thing) with one connector, and a C (gadget) with one connector. So you could have... (coupler . thing) . gadget Because the coupler and the thing would combine to create a component with one spare connector. This would then combine with the gadget to make the final component. However, if you did... coupler . (thing . gadget) Then thing and gadget combine to make a component with no spare connectors. And so the new component and the coupler then fail to combine. Associativity law broken. So, can I adjust my idea to fit the category concept? Or is it just not applicable here? Or am I just misunderstanding the whole concept? -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] edge: compile testing
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 -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] edge: compile testing
On 12/14/2012 07:05 PM, Clark Gaebel wrote: Unacceptable argument type in foreign declaration Thanks for giving it a try. Could you send off a bug report to the OpenAL Haskell module maintainer? sven.pa...@aedion.de (I might offer to do it, but I tried to e-mail him once about a different issue and never heard back. Probably didn't make it through his spam filter.) -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] containers license issue
On 12/13/2012 08:34 AM, Clint Adams wrote: On Wed, Dec 12, 2012 at 11:11:28PM -0800, Chris Smith wrote: That's true. However, haskell.org's fiscal sponsor receives pro bono legal services. I may have been conflating threads, though the response to what I assume was just a lawyer asking a question seems excessive too. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe Just thought I'd mention: It is possible for anyone involved in a FOSS project to get pro bono legal advice from the SFLC, from actual lawyers who are highly familiar with the legal aspects of FOSS licenses: https://www.softwarefreedom.org quote: If you are involved in a Free, Libre and Open Source Software (FLOSS) project in need of legal advice, please email h...@softwarefreedom.org. When seeking legal advice, please use only this address to contact us (unless you are already a client). I'm not sure if they are willing to help those who are trying to /avoid/ making a free software product, but they would likely be willing to answer any generic questions about applicability of the GPLs, derived works, etc. -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] containers license issue
On 12/13/2012 05:54 PM, Richard O'Keefe wrote: On 14/12/2012, at 7:45 AM, Christopher Howard wrote: Intimately familiar with New Zealand law, are they? I couldn't say anything about that, specifically. However, SFLC has an international outreach. From 2011 SFLC news: quote: We are proud to announce a new position at the Software Freedom Law Center: Director of International Programs. Over the past few years SFLC has become an increasingly International organization, working with the European Commission, launching SFLC India, and consulting with governments around the world on issues of free software licensing, policy, and use. Mishi Choudhary, counsel at SFLC and head of SFLC India, has always been at the heart of this work so it is only fitting that she is stepping up to fill the new position. Congratulations to Ms. Choudhary and we all look forward to a stronger international presence ahead. - -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] education or experience?
I'm at something of a crossroads, and I'm hoping to get a bit of free career advice. I really enjoy programming with Haskell (and a few other exotic languages), and was hoping I could eventually make a living in that sort of field. Not rich and famous, necessarily, just enough to get by comfortably. I'm trying to decide, however; should I go back to school, finish my B.S. and pursue a Masters in CompSci? Or would the time (and money) be better spent aggressively pursuing volunteer work for companies, hoping to eventually get the experience and contacts that lead to a paying job? To be honest, I don't really want to go back to school, because I learn a lot faster (and more economically) on my own. However, I'm not sure which path is the fastest, and safest, approach to an actual paycheck. (Also, I'm something of a die-hard FOSS purist, if that affects the discussion at all.) -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] sequential logic
Hi. I was wondering what the various (and especially most simple) approaches one could take for working with (simulating or calculating) sequential logic in Haskell. By sequential logic, I mean like wikipedia describes, where a system is made up of logic gates, whose output is dependent not only on the logic operation of the gate, but on the previous state of the gate. (Like in electronics where the system can be driven by a clock signal or have memory.) Does one have to get into FRP for that sort of thing? Or use some kind of FSM framework? Or is there some kind of fancy state monad suitable for that? Or...? I'm no electronic or digital engineer, but for learning purposes I've been trying to see if I could build an (extremely simple) virtual processor or calculator in Haskell, using only the Bool type and a few of the boolean operators (and functions composed of the aforementioned), reproducing things like half adders and full adders as functions in the program. Of course, I quickly ran into the stateful aspect of the problem, in subjects like clock signal and flip flops. -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
