Re: [Haskell-cafe] Very crazy
On Tue, 25 Sep 2007, Lennart Augustsson wrote: > It's reasonably easy to read. > But you could make it more readable. Type signatures, naming the first > lambda... > It might be reasonable to define something like mapMatrix that happens to be map . map, too. Along with at least a type synonym for matrices. Name domain constructs rather than expecting people to reconstruct them from their implementations, in other words. -- [EMAIL PROTECTED] The task of the academic is not to scale great intellectual mountains, but to flatten them. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Very crazy
Text.printf only has one type. But it is a bit involved. Just use it without worrying exactly how it works. :) Like 's ++ printtf "%g*x%d" x i' On 9/25/07, Andrew Coppin <[EMAIL PROTECTED]> wrote: > > Chaddaï Fouché wrote: > > 2007/9/25, Andrew Coppin <[EMAIL PROTECTED]>: > > > >>> printf don't always perform IO : if you ask it for a String it will > >>> happily turn into sprintf for you, if you use it in the IO Monad, it > >>> will indeed perform IO, but there's nothing fundamentally IO bound in > >>> printf logic. > >>> > >>> > >> That's even *more* impossible... o_O > >> > > > > Why ? > > > > How can one function have more than one type signature? > > ___ > 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] Very crazy
It's reasonably easy to read. But you could make it more readable. Type signatures, naming the first lambda... On 9/25/07, Andrew Coppin <[EMAIL PROTECTED]> wrote: > > While using Haskell, I often find myself writing convoluted > constructions such as this: > > show_system = > unlines . > zipWith > (\l ms -> > "Eq" ++ > show l ++ > ": " ++ > (concat $ intersperse " + " $ zipWith (\n x -> x ++ " x" ++ show > n) [1..] (init ms)) ++ > " = " ++ > last ms > ) > [1..] . > map (map (take 8 . show)) > > And people complain that *Perl* is bad? This function is quite obviously > absurd. I mean, it works, but can *you* figure out what it does without > running it? The question is, can anybody think of a better way to write > this function? (And more generally, functions like it.) > > ___ > 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] Very crazy
On Sep 25, 2007, at 7:25 , Andrew Coppin wrote: Chaddaï Fouché wrote: 2007/9/25, Andrew Coppin <[EMAIL PROTECTED]>: printf don't always perform IO : if you ask it for a String it will happily turn into sprintf for you, if you use it in the IO Monad, it will indeed perform IO, but there's nothing fundamentally IO bound in printf logic. That's even *more* impossible... o_O Why ? How can one function have more than one type signature? Polymorphism via typeclasses. PrintfType is rather hairy, as I said, but it can do the job by having instances for IsString (itself a hack of sorts) and IO. -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] [EMAIL PROTECTED] system administrator [openafs,heimdal,too many hats] [EMAIL PROTECTED] electrical and computer engineering, carnegie mellon universityKF8NH ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Very crazy
> How can one function have more than one type signature? It's called "polymorphism". ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Very crazy
Chaddaï Fouché wrote: 2007/9/25, Andrew Coppin <[EMAIL PROTECTED]>: printf don't always perform IO : if you ask it for a String it will happily turn into sprintf for you, if you use it in the IO Monad, it will indeed perform IO, but there's nothing fundamentally IO bound in printf logic. That's even *more* impossible... o_O Why ? How can one function have more than one type signature? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Very crazy
Chaddaï Fouché wrote: 2007/9/25, Andrew Coppin <[EMAIL PROTECTED]>: Forget PrintfType - I can't even understand the haddoc page yet! (printf performs I/O, yet it is outside the I/O monad. It seems to accept an arbitrary number of arguments, which is obviously impossible. It's *almost* as scary as the original. Although the original will crash your program is you use it wr... oh, so does this one. Cool.) printf don't always perform IO : if you ask it for a String it will happily turn into sprintf for you, if you use it in the IO Monad, it will indeed perform IO, but there's nothing fundamentally IO bound in printf logic. That's even *more* impossible... o_O Well printf crash your program because it can't check if you're arguments correspond to the chain at compile time (quite obviously since the chain itself can be dynamic), but it won't corrupt memory or anything from this kind, so it's arguably much better than the C one. All I know is that in C, any attempt to use printf() has an 80% probability of causing the machine to dump the entire contents of RAM to stdout until it happens upon a zero byte. Probably the most annoying part was all the 0x07 bytes in there. Do you know what a room full of beeping PCs is like? I do... Sometimes when we got bored, we would "race" our PCs to see which one would stop beeping first. (But they stopped that when I worked out how to make mine "win" every race...) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Very crazy
On Tue, Sep 25, 2007 at 10:53:55AM +0100, Andrew Coppin wrote: > Tristan Allwood wrote: >> >> Just to follow those sentiments, the version I knocked out quickly >> looked like: >> (It's not quite the same as the original function, I think I'm lacking a >> map (map (take 8)) on the first line). >> >> showSystems :: Show a => [[a]] -> String >> showSystems = unlines . zipWith showSystem [1..] >> where >> showSystem n as = "Eq" ++ (show n) ++ ": " ++ sum ++ " = " ++ val >> where >> sum = concat . intersperse " + " . zipWith showNum [1..] $ (init >> as) >> val = show . last $ as >> showNum n a = show a ++ " x" ++ show n >> >> > > I'm puzzled - do we have 2 seperate where clauses? Yes there are 2 and no they arn't seperate. The second where clause is nested and is a set of definitioins local to showSystem, and as such can use the bound values of n and as. (But it can also "see" any values bound by showSystems and its where clause (which in this case is just the definition of showSystem). Clear as mud? T -- Tristan Allwood PhD Student Department of Computing Imperial College London ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Very crazy
On Sep 25, 2007, at 5:45 , Andrew Coppin wrote: Still, since Haskell seems to be devoid of any more advanced way of formatting numbers beyond low-level character jiggling... Text.Printf.printf is your friend. -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] [EMAIL PROTECTED] system administrator [openafs,heimdal,too many hats] [EMAIL PROTECTED] electrical and computer engineering, carnegie mellon universityKF8NH ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Very crazy
Brandon S. Allbery KF8NH wrote: On Sep 25, 2007, at 5:56 , Andrew Coppin wrote: More seriously, I have no idea how you'd implement this in Haskell. Presumably the standard show instance for Int, Double, etc. is in native C? You could probably reimplement it in Haskell for the integer case, but not for floating-point... Actually, Text.Printf is pure Haskell. (Very *scary* Haskell: deep type hackery is needed to make it work. Don't try to understand PrintfType. :) Forget PrintfType - I can't even understand the haddoc page yet! (printf performs I/O, yet it is outside the I/O monad. It seems to accept an arbitrary number of arguments, which is obviously impossible. It's *almost* as scary as the original. Although the original will crash your program is you use it wr... oh, so does this one. Cool.) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Very crazy
On Sep 25, 2007, at 5:56 , Andrew Coppin wrote: More seriously, I have no idea how you'd implement this in Haskell. Presumably the standard show instance for Int, Double, etc. is in native C? You could probably reimplement it in Haskell for the integer case, but not for floating-point... Actually, Text.Printf is pure Haskell. (Very *scary* Haskell: deep type hackery is needed to make it work. Don't try to understand PrintfType. :) -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] [EMAIL PROTECTED] system administrator [openafs,heimdal,too many hats] [EMAIL PROTECTED] electrical and computer engineering, carnegie mellon universityKF8NH ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Very crazy
Brandon S. Allbery KF8NH wrote: On Sep 25, 2007, at 5:48 , Andrew Coppin wrote: You've got to be kidding... I went to all the trouble of learning a "scary logic programming language [sic]" just to avoid that damned printf() function! :-/ Enh. :) On the other hand, I do wonder that nobody's written a combinator-based numeric formatting library. They probably have - it's probably based on Peano integers though. :-P More seriously, I have no idea how you'd implement this in Haskell. Presumably the standard show instance for Int, Double, etc. is in native C? You could probably reimplement it in Haskell for the integer case, but not for floating-point... ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Very crazy
Tristan Allwood wrote: Just to follow those sentiments, the version I knocked out quickly looked like: (It's not quite the same as the original function, I think I'm lacking a map (map (take 8)) on the first line). showSystems :: Show a => [[a]] -> String showSystems = unlines . zipWith showSystem [1..] where showSystem n as = "Eq" ++ (show n) ++ ": " ++ sum ++ " = " ++ val where sum = concat . intersperse " + " . zipWith showNum [1..] $ (init as) val = show . last $ as showNum n a = show a ++ " x" ++ show n I'm puzzled - do we have 2 seperate where clauses? Pointsfree and explicit lambda notation I find can be very concise in places, but make it quite hard to reuse or refactor code later - if you can't read it, make a function/variable with a useful name so you can later. Mmm, so just like every other programming language. Theoretically you could write a ten thousand line Pascal program on 1 line - but please don't! Hehe. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Very crazy
On Sep 25, 2007, at 5:48 , Andrew Coppin wrote: Dougal Stanton wrote: In this instance I would suggest: (1) Text.Printf You've got to be kidding... I went to all the trouble of learning a "scary logic programming language [sic]" just to avoid that damned printf() function! :-/ Enh. :) On the other hand, I do wonder that nobody's written a combinator-based numeric formatting library. -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] [EMAIL PROTECTED] system administrator [openafs,heimdal,too many hats] [EMAIL PROTECTED] electrical and computer engineering, carnegie mellon universityKF8NH ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Very crazy
Dougal Stanton wrote: In this instance I would suggest: (1) Text.Printf You've got to be kidding... I went to all the trouble of learning a "scary logic programming language [sic]" just to avoid that damned printf() function! :-/ (2) Pull out some of those things into separate functions with where/let clauses. If it's a matrix you should probably have something like showMatrix = concatMap showRow Since you'll be applying the same procedures to each line of digits. Well, actually more like show_matrix = concat . zipWith show_row [1..] but yeah, this would probably simplify things somewhat. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Very crazy
Neil Mitchell wrote: Hi A nice auxiliary would help: showEqn :: Int -> [Double] -> String showEqn i vs = ... where (add,ans) = (init vs, last vs) Then you can half the complexity. There are probably a few useful functions that aren't in the standard libraries (consperse, joinWith etc) that you could make use of. OK, I'll give that a go... (Actually, at present it's an "augmented matrix", represented as [[Double]]. I'm thinking by making it a matrix and seperate vector, I could reduce the runtime quite significantly by making it much faster to get hold of the RHS.) BTW, one *extremely* common function that I've never seen mentioned anywhere is this one: map2 :: (a -> b) -> [[a]] -> [[b]] map2 f = map (map f) I cannot understand why this isn't already in the standard libraries... You seem to be doing take 8 on the double - what if the double prints out more information than this as the result of show? 100 could end up a bit smaller. The contents of the matrix are random numbers between 0 and 100. The problems happen if one of the numbers turns out to be something like "3.5847368473587e-27" or something. Then it will look many thousands of times BIGGER! ;-) Still, since Haskell seems to be devoid of any more advanced way of formatting numbers beyond low-level character jiggling... ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Very crazy
On Tue, Sep 25, 2007 at 10:31:34AM +0100, Dougal Stanton wrote: > On 25/09/2007, Andrew Coppin <[EMAIL PROTECTED]> wrote: > In this instance I would suggest: > > (1) Text.Printf > (2) Pull out some of those things into separate functions with > where/let clauses. > > If it's a matrix you should probably have something like > > > showMatrix = concatMap showRow > > Since you'll be applying the same procedures to each line of digits. Just to follow those sentiments, the version I knocked out quickly looked like: (It's not quite the same as the original function, I think I'm lacking a map (map (take 8)) on the first line). showSystems :: Show a => [[a]] -> String showSystems = unlines . zipWith showSystem [1..] where showSystem n as = "Eq" ++ (show n) ++ ": " ++ sum ++ " = " ++ val where sum = concat . intersperse " + " . zipWith showNum [1..] $ (init as) val = show . last $ as showNum n a = show a ++ " x" ++ show n Pointsfree and explicit lambda notation I find can be very concise in places, but make it quite hard to reuse or refactor code later - if you can't read it, make a function/variable with a useful name so you can later. Regards, T -- Tristan Allwood PhD Student Department of Computing Imperial College London ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Very crazy
Hi > complex. The input is quite simple (it's a bunch of numbers), the output > is quite simple (it's a neatly formatted string), but the process in the > middle is... a mess. I'd like to find a more readable way of doing stuff > like this. It's not just this specific function; any general hints would > be good. ;-) A nice auxiliary would help: showEqn :: Int -> [Double] -> String showEqn i vs = ... where (add,ans) = (init vs, last vs) Then you can half the complexity. There are probably a few useful functions that aren't in the standard libraries (consperse, joinWith etc) that you could make use of. You seem to be doing take 8 on the double - what if the double prints out more information than this as the result of show? 100 could end up a bit smaller. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Very crazy
On 25/09/2007, Andrew Coppin <[EMAIL PROTECTED]> wrote: > Type signature is > > show_system :: [[Double]] -> String > > It takes a matrix representing a system of equations, and pretty prints > it. Unfortunately, doing complex formatting like that is... well, > complex. The input is quite simple (it's a bunch of numbers), the output > is quite simple (it's a neatly formatted string), but the process in the > middle is... a mess. I'd like to find a more readable way of doing stuff > like this. It's not just this specific function; any general hints would > be good. ;-) In this instance I would suggest: (1) Text.Printf (2) Pull out some of those things into separate functions with where/let clauses. If it's a matrix you should probably have something like > showMatrix = concatMap showRow Since you'll be applying the same procedures to each line of digits. Cheers, D. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Very crazy
Neil Mitchell wrote: Hi And people complain that *Perl* is bad? This function is quite obviously absurd. I mean, it works, but can *you* figure out what it does without running it? No. Can you say what the intention of this code is? Maybe a few examples? The type signature? That way I think people will be more able to give you hints. Type signature is show_system :: [[Double]] -> String It takes a matrix representing a system of equations, and pretty prints it. Unfortunately, doing complex formatting like that is... well, complex. The input is quite simple (it's a bunch of numbers), the output is quite simple (it's a neatly formatted string), but the process in the middle is... a mess. I'd like to find a more readable way of doing stuff like this. It's not just this specific function; any general hints would be good. ;-) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Very crazy
Hi > show_system = > unlines . > zipWith > (\l ms -> > "Eq" ++ > show l ++ > ": " ++ > (concat $ intersperse " + " $ zipWith (\n x -> x ++ " x" ++ show > n) [1..] (init ms)) ++ > " = " ++ > last ms > ) > [1..] . > map (map (take 8 . show)) > > And people complain that *Perl* is bad? This function is quite obviously > absurd. I mean, it works, but can *you* figure out what it does without > running it? No. Can you say what the intention of this code is? Maybe a few examples? The type signature? That way I think people will be more able to give you hints. Generally, I find list comprehensions to be a good way out of general listy mess. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Very crazy
While using Haskell, I often find myself writing convoluted constructions such as this: show_system = unlines . zipWith (\l ms -> "Eq" ++ show l ++ ": " ++ (concat $ intersperse " + " $ zipWith (\n x -> x ++ " x" ++ show n) [1..] (init ms)) ++ " = " ++ last ms ) [1..] . map (map (take 8 . show)) And people complain that *Perl* is bad? This function is quite obviously absurd. I mean, it works, but can *you* figure out what it does without running it? The question is, can anybody think of a better way to write this function? (And more generally, functions like it.) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
