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Help ? :)
by Patty Fong 03 Nov '03

03 Nov '03

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RE: fixed point
by Dean Herington 01 Nov '03

01 Nov '03

At 11:15 AM -0500 2003/10/31, Harris, Andrew wrote: > Hi - > I am trying to work out how the following function using "fix" is > evaluated. I am hoping someone could look at my step-by-step breakdown > of how I think evaluation works and see if I'm correct. My main > question is how the order of operation (fixity?) is understood in going > from step [3] to [4], if this is indeed how the evaluation would take > place. > > Any help is appreciated, > -andrew > > Here's the Haskell function: > > --- > fix f = f (fix f) > > wierdFunc2 x y z = if y - z > z then x (y-z) z > else y - z > > myRemainder = fix wierdFunc2 > --- > > Here's my "evaluation": You're pretty close. I've noted a couple of differences below. > myRemainder 12 5 -- [1] > = > fix wierdFunc2 12 5 -- [2] by substitution > = > wierdFunc2 fix wierdFunc2 12 5 -- [3] apply "fix" wierdfunc2 (fix wierdFunc2) 12 5 > = > wierdFunc2 myRemainder 12 5 -- [4] by substitution (?) No, equations "rewrite" only "from left to right". Skip the step above and the step below. > = > myRemainder 7 5 -- [5] apply "wierdFunc2" > = > fix wierdFunc2 7 5 -- [6] by substitution > = > wierdFunc2 fix wierdFunc2 7 5 -- [7] apply "fix" Similarly, the above needs (fix wierdFunc2) to be parenthesized. > = > wierdFunc2 myRemainder 7 5 -- [8] by substitution (?) Skip the above step. > = > 2 -- [9] apply "wierdFunc2" Dean

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newbie question regarding type declarations
by gangadhar npk 31 Oct '03

31 Oct '03

hi, I am a newbie to Haskell. I am reading the tutorial by Hal Daume III. Regarding the function types which are an extension of lambda calculus, I was wondering if at all it is possible to write a type that would return two values as the output - something like a square function which would take a pair and return a pair. I tried this, but there are errors square :: (Num a, Num b) => (a ,b) square (x , y) = (x*x , y*y) How can I specify that the square functions output would be a pair ? thank you gangadhar

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Monad @ Microsoft
by Josef Svenningsson 31 Oct '03

31 Oct '03

OK, this one is just too good not to post about it. Microsoft has developed a now command line interface. Guess what they call it? Read it here: http://slashdot.org/articles/03/10/31/1346201.shtml?tid=185&tid=190&tid=201 Well, it seems Simoj PJ is doing a good job introducting functional programming at MS although his methods are subtle in the extreme :-) /Josef

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RE: fixed point
by Harris, Andrew 31 Oct '03

31 Oct '03

Hi - I am trying to work out how the following function using "fix" is evaluated. I am hoping someone could look at my step-by-step breakdown of how I think evaluation works and see if I'm correct. My main question is how the order of operation (fixity?) is understood in going from step [3] to [4], if this is indeed how the evaluation would take place. Any help is appreciated, -andrew Here's the Haskell function: --- fix f = f (fix f) wierdFunc2 x y z = if y - z > z then x (y-z) z else y - z myRemainder = fix wierdFunc2 --- Here's my "evaluation": myRemainder 12 5 -- [1] = fix wierdFunc2 12 5 -- [2] by substitution = wierdFunc2 fix wierdFunc2 12 5 -- [3] apply "fix" = wierdFunc2 myRemainder 12 5 -- [4] by substitution (?) = myRemainder 7 5 -- [5] apply "wierdFunc2" = fix wierdFunc2 7 5 -- [6] by substitution = wierdFunc2 fix wierdFunc2 7 5 -- [7] apply "fix" = wierdFunc2 myRemainder 7 5 -- [8] by substitution (?) = 2 -- [9] apply "wierdFunc2"

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newbie question regarding type declarations
by gangadhar npk 31 Oct '03

31 Oct '03

hi, I am a newbie to Haskell. I am reading the tutorial by Hal Daume III. Regarding the function types which are an extension of lambda calculus, I was wondering if at all it is possible to write a type that would return two values as the output - something like a square function which would take a pair and return a pair. I tried this, but there are errors square :: (Num a, Num b) => (a ,b) square (x , y) = (x*x , y*y) How can I specify that the square functions output would be a pair ? thank you gangadhar

1 0

Heap profiling in GHC broken?
by Markus.Schnell＠infineon.com 30 Oct '03

30 Oct '03

Hi. When I tried to profile my program in search for space leaks, it core dumped on me (actually on Win2000/Cygwin). I'm using ghc 6.0.1. Does anybody know what could be the problem? (To be more precise: any +RTS -h_ options make problems, +RTS -p works fine. I get a message meaning the equivalent of "statement in '0x0058db43' points to memory in '0xfffffffc'. Could not read.") Cheers, Markus -- Markus Schnell

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Haskell Asignement not working
by Rachel Reid 29 Oct '03

29 Oct '03

My code is --1)Define a function bLine to give a line of horizontal #s import Pictures sb, sw :: Picture bLine :: Int -> Picture bLine n ) |n==0 = ) |n>0 = `sideBySide` sb (bLine (n-1)) and when running Hugs, it says that there is a <unexpected symbol "#"> in line 9 which is bLine n ). There was a hash sign previously, but I have reloaded Hugs since then. can you help Thanks Rachel

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fixed point
by Harris, Andrew 29 Oct '03

29 Oct '03

Hi - I am trying to do Exercise 9.9 in HSOE; and I've come up with an answer that works but I'm not sure if it answers the question properly. The problem is: The Question: ------------- Suppose we define a function "fix" as: fix f = f (fix f) Suppose further we have a recursive function: remainder :: Integer -> Integer -> Integer remainder a b = if a < b then a else remainder (a - b) b Rewrite this function using "fix" so that it's not recursive. My Answer: ---------- wierdFunc x y z = if y - z > z then ((\a b c -> a b c) x (y-z) z) else ((\a b c -> a b c) (\d e -> d) (y-z) z) myRemainder = fix wierdFunc My Question: ------------ Does the ((\a b c -> a b c) x (y-z) z) mean that I've not removed the recursion? I was assuming that I was returning a function that is to be evaluated and not actually doing any recursion. That's why I thought I answered the question. However, I have a headache now and would like another opinion. thanks, -andrew

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Cast from and to CChar
by Christian Buschmann 28 Oct '03

28 Oct '03

Hi! I've got following problem. If I enter in ghci following line: Prelude Foreign.C> castCCharToChar $ castCharToCChar 'ü' I would expect that this returns 'ü', but it returns '\252'. Is this the correct behaviour? Or am I doing something wrong? Or are there any problems with language specific characters and CChar? thanks Christian B.

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