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a more practical version of getLine???
by Rich 26 Feb '02

26 Feb '02

Hi, I'm writing a program for my final project at uni and I've come across the following annoying bug in my program. Basically, I have an interactive text prompt and I wish to be able to write commands into the prompt. I am currently using the function 'getLine', which as it's name suggests reads a line of text from the prompt. Unfortunately, when the delete key is used while writing to the prompt, the output differs (so typing "loaf" then 'delete' and then "d" does not seem to produce the same output as typing "load"). Also, the left and right arrow keys don't work, as they do in any normal text prompt. Any suggestins as to an alternative method to read the input??? (I'm by no means a Haskell expert btw, so I may have to be spoon fed!) thanks for your help, Rich.

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Help
by Juan M. Duran 25 Feb '02

25 Feb '02

Hi, I need to parse a string to a list of integer, like this: "12 32\n15...." to [12,32,15...] f :: String -> [Int] What I´ve found is the function "words" which does words :: String -> [String] it is in the Prelude.hs then if I have something like "12 32\n15..." with words I get ["12","32","15"...] which is cool but not exactly what I need. Would you help me? Thanks J. ------------------------------------ Porque la única lucha que se pierde, es la que se abandona, ¡Ni un paso atrás!

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RE: Monadic Call/CC?
by Simon Marlow 25 Feb '02

25 Feb '02

> At 2002-02-23 07:55, Marcin 'Qrczak' Kowalczyk wrote: > > >It's in GHC in module MonadCont, together with a monad transformer > >providing continuations and some instances. > > Could this sort of thing _please_ be added to > <http://www.haskell.org/ghc/docs/latest/set/book-hslibs.html> > or somewhere? Is this documented somewhere? My apologies for the lack of documentation for some of these libraries, and the generally poor state of the doumentation for hslibs. Some of the libraries come from external sources, and in some cases the authors didn't provide documentation, or provided it in a form that we couldn't use directly. For the next release of GHC, I'm hoping we can do a much better job, though not just by writing more documentation but by generating more of it automatically from the source code. That's the plan; we don't have anything concrete yet. Cheers, Simon

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Re: Graphs
by David Feuer 25 Feb '02

25 Feb '02

I seem to remember an article about functional graph algorithms using extra-lazy arrays. Anyone know if these arrays have appeared in any mainstream implementation? David Feuer

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RE: Survival of generic-classes in ghc
by Simon Peyton-Jones 25 Feb '02

25 Feb '02

| > Another possiblity would be to make the ConCls class look like this | > class ConCls c where | > name :: String | > arity :: Int | > ...etc... | > | > Now we'd have to give an explicit type argument at the call site: | > | > show {| Constr c t |} (Con x) = (name {| c |}) ++ show x | > | > I quite like the thought of being able to supply explicit type | > arguments.... but I don't konw how to speak about the order of type | > parameters. What order does map takes its two type parameters in? | | Sorry, this seems like a non-sequitur to me? | | 'map' has type '(a->b) -> [a] -> [b]'; supplying explicit | type parameters would mean giving values to 'a' and 'b'. If | I wanted to propose notation for this, I would suggest, e.g., | (map :: (String -> Int) -> [String] -> [Int]) length | ["Hello", "World"] | | 'name' (above) has type 'String'; the '{| c |}' is not | providing a type parameter in the same sense. Yes it is. 'name' would have type forall c. ConCls c => String It requires a type argument, just like map. Simon

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RE: Survival of generic-classes in ghc
by Simon Peyton-Jones 25 Feb '02

25 Feb '02

| As long as we're reifying everything in sight, why not | simplify the design problem and reify the constructor dictionaries? Because the generic function may be building the contructor not taking it apart. (Think of a generic read function). So there is no reified constructor to deconstruct. This is discussed in the generic classes paper. It has to be done by recursion over the type. It's emphatically not just an efficiency issue. Simon

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RE: Survival of generic-classes in ghc
by Simon Peyton-Jones 25 Feb '02

25 Feb '02

| I'm disturbed by the idea of adding explicit type application | and the like to Haskell. Haskell language extensions are | rapidly becoming a riotous array of confusing syntax and | twisty semantic corners. From an experimenter's standpoint, | this isn't so bad. However, many of these extensions are | incredibly useful, and there's a lot of code relying upon | them. This creates pressure (from both users and | implementors) to immortalize the existing, grubby | implementations. The result? An incomprehensible, byzantine language. Yes, that's a danger. My own hope is that the practial experience of using and programming with these various features will lead us slowly to a realisation of some underlying unifying approaches or principles. That is what the rest of you message is reaching for -- which is great. But it easier to identify the problem than to come up with a satisfactory solution, and I for one do not have one. But I think it would be great to find one. Simon

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(no subject)
by Tom Bevan 25 Feb '02

25 Feb '02

Hi, I've come across this sort of data constructor below many times but I'm not really sure how to use it. Can someone please point me to the right section in the documentation? In particular, I want to know how to create a calendar time and how to access the fields . Tom data CalendarTime = CalendarTime { ctYear :: Int, ctMonth :: Month, ctDay, ctHour, ctMin, ctSec :: Int, ctPicosec :: Integer, ctWDay :: Day, ctYDay :: Int, ctTZName :: String, ctTZ :: Int, ctIsDST :: Bool } deriving (Eq, Ord, Read, Show)

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Re: (no subject)
by Ashley Yakeley 25 Feb '02

25 Feb '02

At 2002-02-24 22:46, Tom Bevan wrote: >I've come across this sort of data constructor below many times but I'm >not really sure how to use it. Can someone please point me to the right >section in the documentation? http://haskell.org/onlinereport/decls.html#sect4.2.1 "Labelled Fields" >In particular, I want to know how to create a calendar time and how to >access the fields . > >Tom > >data CalendarTime = CalendarTime { > ctYear :: Int, > ctMonth :: Month, > ctDay, ctHour, ctMin, ctSec :: Int, > ctPicosec :: Integer, > ctWDay :: Day, > ctYDay :: Int, > ctTZName :: String, > ctTZ :: Int, > ctIsDST :: Bool > } deriving (Eq, Ord, Read, Show) Basically it's equivalent to this: data CalendarTime = CalendarTime Int Month Int Int Int Int Integer Day Int String Int Bool deriving (Eq, Ord, Read, Show); ctYear (CalendarTime x _ _ _ _ _ _ _ _ _ _ _) = x; ctMonth (CalendarTime _ x _ _ _ _ _ _ _ _ _ _) = x; ctDay (CalendarTime _ _ x _ _ _ _ _ _ _ _ _) = x; etc. ...but you can also use the labelled fields to construct: CalendarTime { ctYear = 2002, ctMonth = 2, ... } -- Ashley Yakeley, Seattle WA

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Magnets supplier located.
by LEWIS＠haskell.org 24 Feb '02

24 Feb '02

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