Re: [Haskell-cafe] message passing style like in Haskell?
On Fri, Jun 20, 2008 at 07:57:58AM +0200, Ketil Malde wrote: Albert Y. C. Lai [EMAIL PROTECTED] writes: While we are kind of on this topic, what makes the characters ħ þ prefix operator by default, while º and most other odd ones infix? alphanumeric vs non-alphanumeric Testing this, I find that isAlpha is True also for 'º', but as the OP claims, Haskell will use it as a(n infix) symbol. This is a bug in GHC. The characters = '\255' were done specially, but incorrectly for many of those = '\128'. I'll fix it, probably by just removing the specialisation for them. Thanks Ian ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] message passing style like in Haskell?
After some fiddling with this style, here is what I came up with for the 8 queens problem in the 99 problem set. It's quite entertaining ... ( note: it's brute force and requires a combination library ) queens2 n = n.permutations.filter all_satisfied where all_satisfied queens = queens.diff_col queens.diff_diag diff_col queens = queens.unique.is queens diff_diag queens = n .combinations 2 .map (map (subtract 1)) .map (id flip cherry_pick queens) .any same_dist.not where same_dist (row_pair, col_pair) = row_pair.foldl1 (-).abs == col_pair.foldl1 (-).abs -- generic helper cherry_pick ids xs = ids.map (xs !!) is a b = a == b unique xs = nub xs Guess this can conclude this experiment :) jinjing On Sun, Jun 22, 2008 at 1:10 AM, Ian Lynagh [EMAIL PROTECTED] wrote: On Fri, Jun 20, 2008 at 07:57:58AM +0200, Ketil Malde wrote: Albert Y. C. Lai [EMAIL PROTECTED] writes: While we are kind of on this topic, what makes the characters ħ þ prefix operator by default, while º and most other odd ones infix? alphanumeric vs non-alphanumeric Testing this, I find that isAlpha is True also for 'º', but as the OP claims, Haskell will use it as a(n infix) symbol. This is a bug in GHC. The characters = '\255' were done specially, but incorrectly for many of those = '\128'. I'll fix it, probably by just removing the specialisation for them. Thanks Ian ___ 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] message passing style like in Haskell?
jinjing [EMAIL PROTECTED] writes: Any way here's the code: module Dot where import Prelude hiding ( (.) ) (.) :: a - (a - b) - b a . f = f a infixl 9 . Isn't this (roughly?) the same as flip ($)? As a side note, may I advise you to use another symbol, and leave the poor dot alone? Overloading it as a module separator is bad enough. If you have a keyboard that allows greater-than-ascii input, there are plenty of options: « » ¡ £ ¥ ł € ® ª... comparing: encode xs = map (\x - (length x,head x)) (group xs) encode xs = xs.group.map token where token x = (x.length, x.head) To be fair, you could write the first line as: encode xs = map token (group xs) where token x = (length x, head x) I'm not normally too enthusiastic about point-free style, but when the left and right side of the = both end with the same term, there's really no need to name them, so: encode = map token . group where token x = (length x, head x) -- using function composition (.), not your definition I'm not sure that would work with left-to-right composition. I found starting with data and working my way to a solution seems to be easier to think with, or maybe it's just me ... For monadic code, there default is = and which pass things forward. There's also = which goes the other way - so I guess opinions differ. -k -- If I haven't seen further, it is by standing in the footprints of giants ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] message passing style like in Haskell?
On Thu, 2008-06-19 at 11:33 +0800, jinjing wrote: Hi guys, This is my second attempt to learn Haskell :) Any way here's the code: module Dot where import Prelude hiding ( (.) ) (.) :: a - (a - b) - b a . f = f a infixl 9 . Note that if you redefine (.) composition to be backward application (flip ($)) then nobody will understand your programs. It's also quite probably that after reading your own code for a while that you'll not understand the code that everyone else writes either! :-) If you want an operator like that, I suggest picking some other symbol. Duncan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] message passing style like in Haskell?
On 2008.06.19 11:33:56 +0800, jinjing [EMAIL PROTECTED] scribbled 0.5K characters: Hi guys, This is my second attempt to learn Haskell :) Any way here's the code: module Dot where import Prelude hiding ( (.) ) (.) :: a - (a - b) - b a . f = f a infixl 9 . So for example, 99 questions: Problem 10 (*) Run-length encoding of a list. comparing: encode xs = map (\x - (length x,head x)) (group xs) to encode xs = xs.group.map token where token x = (x.length, x.head) I found starting with data and working my way to a solution seems to be easier to think with, or maybe it's just me ... What is your thought? Jinjing http://cgi.cse.unsw.edu.au/~dons/blog/2007/07 sez: encode = map (length head) . group decode = concatMap (uncurry replicate) for a different twist on your approach using arrows. -- gwern Kerry W NAVSVS industrial Parvus NAVWAN ISM 8182 NRC Reno signature.asc Description: Digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] message passing style like in Haskell?
* On Thursday, June 19 2008, Ketil Malde wrote: As a side note, may I advise you to use another symbol, and leave the poor dot alone? Overloading it as a module separator is bad enough. If you have a keyboard that allows greater-than-ascii input, there are plenty of options: « » ¡ £ ¥ ł € ® ª... And even if you have a plain us layout in hardware, you can use us-international layout (or whatever it is called). So we can make haskell sort of like apl... While we are kind of on this topic, what makes the characters ħ þ prefix operator by default, while º and most other odd ones infix? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] message passing style like in Haskell?
2008/6/19 jinjing [EMAIL PROTECTED]: encode xs = xs.group.map token where token x = (x.length, x.head) Working in this direction is a question of taste, but the choice of the dot for the operator is a pretty bad idea... On the other hand, my favourite would be : encode = map (length head) . group -- Jedaï ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] message passing style like in Haskell?
On Thu, Jun 19, 2008 at 3:35 AM, Ketil Malde [EMAIL PROTECTED] wrote: jinjing [EMAIL PROTECTED] writes: Any way here's the code: module Dot where import Prelude hiding ( (.) ) (.) :: a - (a - b) - b a . f = f a infixl 9 . Isn't this (roughly?) the same as flip ($)? As a side note, may I advise you to use another symbol, and leave the poor dot alone? Overloading it as a module separator is bad enough. If you have a keyboard that allows greater-than-ascii input, there are plenty of options: « » ¡ £ ¥ ł € (R) ª... Note that there already is a standard symbol for this, () from Control.Arrow. Well, actually () is more general than backwards function composition, so maybe making your own symbol is still a good idea while you're learning. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] message passing style like in Haskell?
Adam Vogt wrote: While we are kind of on this topic, what makes the characters ħ þ prefix operator by default, while º and most other odd ones infix? alphanumeric vs non-alphanumeric ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] message passing style like in Haskell?
On Thu, 2008-06-19 at 15:24 -0400, Brent Yorgey wrote: On Thu, Jun 19, 2008 at 3:35 AM, Ketil Malde [EMAIL PROTECTED] wrote: jinjing [EMAIL PROTECTED] writes: Any way here's the code: module Dot where import Prelude hiding ( (.) ) (.) :: a - (a - b) - b a . f = f a infixl 9 . Isn't this (roughly?) the same as flip ($)? As a side note, may I advise you to use another symbol, and leave the poor dot alone? Overloading it as a module separator is bad enough. If you have a keyboard that allows greater-than-ascii input, there are plenty of options: « » ¡ £ ¥ ł € ® ª... Note that there already is a standard symbol for this, () from Control.Arrow. Well, actually () is more general than backwards function composition, so maybe making your own symbol is still a good idea while you're learning. Application, not composition. Cont's return would work if it weren't for the wrapping. Similarly, (=) for the Id monad. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] message passing style like in Haskell?
Albert Y. C. Lai [EMAIL PROTECTED] writes: While we are kind of on this topic, what makes the characters ħ þ prefix operator by default, while º and most other odd ones infix? alphanumeric vs non-alphanumeric Testing this, I find that isAlpha is True also for 'º', but as the OP claims, Haskell will use it as a(n infix) symbol. Neither does isSymbol (all False), isLetter (all True), isMark (False), nor isPunctuation (Fals) help to separate these. The HR defines uniSymbol- any Unicode symbol or punctuation but I couldn't find any clear way to identify of these. -k -- If I haven't seen further, it is by standing in the footprints of giants ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
