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Re: partial application
by C.Reinke 19 Mar '02

19 Mar '02

> ..I was thinking of the following syntax. I orginally had the > idea for C++, where you can't do partial application at all. ? FC++: Functional Programming in C++ http://www.cc.gatech.edu/~yannis/fc++/ (I wouldn't be defending C++ otherwise, but its set of things you can't do at all must be a lot smaller than in other languages;-) They seem to support the _ notation, btw. Laurent Dami had a lambda-calculus variant that allowed for partial application by name instead of by position (amongst several other interesting features:) http://cui.unige.ch/~dami/publis.html Claus -- Research Opportunity: Refactoring Functional Programs (UKC) Closing date: Friday 22 March 2002 !! http://www.cs.ukc.ac.uk/vacancies_dir/r02-24.html

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Re: partial application
by Peter G. Hancock 19 Mar '02

19 Mar '02

Apropos of section notation, don't forget flip, alias the C combinator. It allows you to express partial applications "to the next argument but one" is in operator section notation. We can express (usually horribly) any affine lambda-abstraction with flip, (.), id and const. Peter Hancock

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Re: Hiring Haskell programmers
by John Hughes 15 Mar '02

15 Mar '02

> Depends where you are, I guess. In Sydney, it would be > easy. We are teaching Haskell to about 1500 first-year > students every year. > Melbourne University is teaching similar numbers (perhaps slightly less; probably more than 1000) of first-year students Haskell every year. -- Nick Nethercote njn25(a)cam.ac.uk Goodness me, we're only teaching 160 here in Gothenburg! I feel inadequate! However, we're teaching 20 or so a year to an advanced level, so I reckon there are around 100 really skillful Haskell programmers in Gothenburg by now. That should be enough for a while... John Hughes

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Re: Continuation Passing Style
by Ashley Yakeley 15 Mar '02

15 Mar '02

At 2002-03-14 16:10, Tom Bevan wrote: >I noticed that Ralf Hinze posted a CPS monad yesterday. He did? Anyway I have one here: <http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/*checkout*/hscheme/Source/C ontinuationPassing.hs?rev=HEAD&content-type=text/plain> Basically it's this: newtype CPS ex p a = MkCPS {unCPS :: (ex -> p) -> (a -> p) -> p}; 'ex' is exception, so that I can make it an instance of MonadError. >Would someone be kind enough to post a simple example of a function that >uses CPS. Once you've made it an instance of Monad, of course you can just use 'do' notation. But I use CPS here (for my Scheme interpreter) because you can do call-with-current-continuation. -- Ashley Yakeley, Seattle WA

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RE: Date Sorting Round Three
by Garner, Robin 15 Mar '02

15 Mar '02

The problem you are trying to come to grips with here is one of the watersheds in the learning curve that most people learning Haskell encounter, namely how to use values returned in Monads. I could point out that you have already solved the same problem when you used getLine. The question you need to ask yourself is not, "how do I convert a value of type IO String to a value of type String", but "how do I use the result of a calculation within the IO Monad". Look at where you've already solved the problem, and the answer will appear almost immediately. Robin -----Original Message----- From: Michael Ruth [mailto:meruth@hotmail.com] Sent: Friday, 15 March 2002 11:30 To: haskell-cafe(a)haskell.org Subject: Date Sorting Round Three long set of code here, I think I figured out what you all were telling me. Compose small functions then compose bigger functions from smaller functions and so on... The problem I am having is I have an (IO String) where I need a (String) and it reports it as such: ERROR "C:\Documents and Settings\drunkenmike\My Documents\Programming\Csci4501\H askell\datesort.hs":41 - Type error in application *** Expression : separateIntoLines (getInput x) *** Term : getInput x *** Type : IO String *** Does not match : [Char] I am gonna mark line 41 with a * at the beginning of the line. I have been looking high and low for the answer to IOString -> String.... all I think I need to do (I think anyways) By the way, thanks to everyone for their help. import IO --- -- Control Flow --- datesort :: IO() datesort = do { putStr "Enter a filename: "; theFile <- getLine; sortAndOutput (readInAndGetReady theFile); } -- -- Composite functions -- 1) Read in & Get ready to sort -- 2) sort & output -- -- readInAndGetReady :: String -> [String] *readInAndGetReady x = fixDates (makeSortableDates (linesToDates (separateIntoLines (getInput x)))) sortAndOutput :: [String] -> IO() sortAndOutput x = writeTheFile (getOutput (makePrintableDates (qsort x))) -- -- Make the date printable. Printable means a string consisting of -- dates in the form dd mm yyyy (more or less undoes the make sortable f x) -- makePrintableDates :: [String] -> [String] makePrintableDates x = map makePrintableDate x -- -- Make the date printable. Printable means a string consisting of -- dates in the form dd mm yyyy (more or less undoes the make sortable f x) -- makePrintableDate :: String -> String makePrintableDate x = unwords (reverse (words x)) -- -- Make all the dates sortable. Sortable means a string consisting of -- dates in the form yyyy mm dd -- makeSortableDates :: [[String]] -> [String] makeSortableDates x = map makeSortableDate x -- -- Make the date sortable. Sortable means a string consisting of -- dates in the form yyyy mm dd -- makeSortableDate :: [String] -> String makeSortableDate x = unwords (reverse x) -- -- Get the input from the given file -- getInput :: String -> IO String getInput myfile = readFile myfile -- -- Seperate the input file into an list of Strings -- separateIntoLines :: String -> [String] separateIntoLines str = lines str -- -- Transform all the lines into dates -- linesToDates :: [String] -> [[String]] linesToDates x = map lineToDate x -- -- Transform the lines into dates -- lineToDate :: String -> [String] lineToDate x = words x -- -- Transform the dates into lines -- getOutput :: [String] -> String getOutput x = unlines x -- -- Fix all the dates so that they are in the form 0x if x < 10 -- fixDates:: [String] -> [String] fixDates x = map fixPrefixes x -- -- Fix the dates so that they are in the form 0x if x < 10 -- fixPrefixes :: String -> String fixPrefixes p | p == "1" = "01" | p == "2" = "02" | p == "3" = "03" | p == "4" = "04" | p == "5" = "05" | p == "6" = "06" | p == "7" = "07" | p == "8" = "08" | p == "9" = "09" | otherwise = p -- -- Quicksort the List of strings -- qsort :: [String] -> [String] qsort [] = [] qsort (x:xs) = qsort elts_lt_x ++ [x] ++ qsort elts_greq_x where elts_lt_x = [y | y <- xs, y < x] elts_greq_x = [y | y <- xs, y >= x] -- -- Write the ouput string to a file -- writeTheFile :: String -> IO() writeTheFile x = writeFile "output.txt" x _________________________________________________________________ Chat with friends online, try MSN Messenger: http://messenger.msn.com _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

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Date Sorting Round Three
by Michael Ruth 15 Mar '02

15 Mar '02

long set of code here, I think I figured out what you all were telling me. Compose small functions then compose bigger functions from smaller functions and so on... The problem I am having is I have an (IO String) where I need a (String) and it reports it as such: ERROR "C:\Documents and Settings\drunkenmike\My Documents\Programming\Csci4501\H askell\datesort.hs":41 - Type error in application *** Expression : separateIntoLines (getInput x) *** Term : getInput x *** Type : IO String *** Does not match : [Char] I am gonna mark line 41 with a * at the beginning of the line. I have been looking high and low for the answer to IOString -> String.... all I think I need to do (I think anyways) By the way, thanks to everyone for their help. import IO --- -- Control Flow --- datesort :: IO() datesort = do { putStr "Enter a filename: "; theFile <- getLine; sortAndOutput (readInAndGetReady theFile); } -- -- Composite functions -- 1) Read in & Get ready to sort -- 2) sort & output -- -- readInAndGetReady :: String -> [String] *readInAndGetReady x = fixDates (makeSortableDates (linesToDates (separateIntoLines (getInput x)))) sortAndOutput :: [String] -> IO() sortAndOutput x = writeTheFile (getOutput (makePrintableDates (qsort x))) -- -- Make the date printable. Printable means a string consisting of -- dates in the form dd mm yyyy (more or less undoes the make sortable f x) -- makePrintableDates :: [String] -> [String] makePrintableDates x = map makePrintableDate x -- -- Make the date printable. Printable means a string consisting of -- dates in the form dd mm yyyy (more or less undoes the make sortable f x) -- makePrintableDate :: String -> String makePrintableDate x = unwords (reverse (words x)) -- -- Make all the dates sortable. Sortable means a string consisting of -- dates in the form yyyy mm dd -- makeSortableDates :: [[String]] -> [String] makeSortableDates x = map makeSortableDate x -- -- Make the date sortable. Sortable means a string consisting of -- dates in the form yyyy mm dd -- makeSortableDate :: [String] -> String makeSortableDate x = unwords (reverse x) -- -- Get the input from the given file -- getInput :: String -> IO String getInput myfile = readFile myfile -- -- Seperate the input file into an list of Strings -- separateIntoLines :: String -> [String] separateIntoLines str = lines str -- -- Transform all the lines into dates -- linesToDates :: [String] -> [[String]] linesToDates x = map lineToDate x -- -- Transform the lines into dates -- lineToDate :: String -> [String] lineToDate x = words x -- -- Transform the dates into lines -- getOutput :: [String] -> String getOutput x = unlines x -- -- Fix all the dates so that they are in the form 0x if x < 10 -- fixDates:: [String] -> [String] fixDates x = map fixPrefixes x -- -- Fix the dates so that they are in the form 0x if x < 10 -- fixPrefixes :: String -> String fixPrefixes p | p == "1" = "01" | p == "2" = "02" | p == "3" = "03" | p == "4" = "04" | p == "5" = "05" | p == "6" = "06" | p == "7" = "07" | p == "8" = "08" | p == "9" = "09" | otherwise = p -- -- Quicksort the List of strings -- qsort :: [String] -> [String] qsort [] = [] qsort (x:xs) = qsort elts_lt_x ++ [x] ++ qsort elts_greq_x where elts_lt_x = [y | y <- xs, y < x] elts_greq_x = [y | y <- xs, y >= x] -- -- Write the ouput string to a file -- writeTheFile :: String -> IO() writeTheFile x = writeFile "output.txt" x _________________________________________________________________ Chat with friends online, try MSN Messenger: http://messenger.msn.com

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Continuation Passing Style
by Tom Bevan 15 Mar '02

15 Mar '02

I noticed that Ralf Hinze posted a CPS monad yesterday. Would someone be kind enough to post a simple example of a function that uses CPS. Thanks Tom

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(no subject)
by 정종길 15 Mar '02

15 Mar '02

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Hiring Haskell programmers
by Mark Carroll 14 Mar '02

14 Mar '02

How easy is it to hire reasonable Haskell programmers? Of course, this may mean, hiring people with the aptitude and interest to quickly learn Haskell. Has anyone any experience of this that they can share? -- Mark

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Date Sorting...
by Michael Ruth 14 Mar '02

14 Mar '02

Hello, I am pretty new to Functional programming, and I am having the following problem. I need to sort a list of dates provided in an input file. One date per line.. day month year is the order. And each is represented by integers seperated by spaces. And once the list is sorted output the results to a file. I having trouble knowing where to start. This is what I was thinking the best line of attack was: --read in the lines one by one into a list --then iterate thru the list while breaking the strings into [Int] list -- of 3 elements [day,month,year] --then quicksort overall list --then print out overall list line by line I understand this is a imperative approach, but this is the way I was taught how to program, well that and OOP. How do I go about writing this in a functional sense ? And is there another way to do this AKA another plan of attack ?. Thanks very much for your time and consideration. Michael _________________________________________________________________ Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp.

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