Embedding newlines into a string? [Was: Re: [Haskell-cafe] Separate a string into a list of strings]
A friend and I were working on a Haskell version of
Towers of Hanoi yesterday, and I tried writing out the
program today, but got stuck on outputting newlines as
part of the string; viz:
hanoi :: Int - String
hanoi n = hanoi_helper 'a' 'b' 'c' n
hanoi_helper :: Char - Char - Char - Int - String
hanoi_helper source using dest n
| n == 1 = putStrLn Move ++ show source ++ to
++ show dest ++ . ++ show '\n'
| otherwise = hanoi_helper source dest using (n-1)
++ hanoi_helper source using dest 1
++ hanoi_helper using source
dest (n-1)
The problem is that the newlines ('\n') get embedded
as escaped newlines into the output string, instead of
as newlines.
E.g.,
Hugs :load hanoi.hs
Main hanoi 2
Move 'a' to 'b'.'\\n'Move 'a' to 'c'.'\\n'Move 'b' to
'c'.'\\n'
Instead, what I want is the following:
Hugs :load hanoi.hs
Main hanoi 2
Move 'a' to 'b'.
Move 'a' to 'c'.
Move 'b' to 'c'.
However, when I try to use putStrLn to avoid this
problem, as follows:
| n == 1 = putStrLn Move ++ show source ++ to
++ show dest ++ . ++ show '\n'
the compiler generates the following error:
ERROR file:hanoi.hs:6 - Type error in application
*** Expression : putStrLn Move ++ show source
++ to ++ show dest ++ . ++ show '\n'
*** Term : putStrLn Move
*** Type : IO ()
*** Does not match : [Char]
Simply changing the type signature does not solve this
problem.
I searched through the past messages on this list, and
came up with the message below, but simply quoting the
newlines as '\n' doesn't seem to help.
Does anybody know a way to embed a newline into a
string as output of type String of a function so that
the newline characters are not escaped?
Benjamin L. Russell
--- Jared Updike [EMAIL PROTECTED] wrote:
Funny. I have a module called Useful.hs with some of
these same sorts
of functions. (coming from Python where I used
.split(',') and
.replace('\r', '') and such a lot):
--
module Useful where
import List ( intersperse, tails )
import Numeric ( readHex )
hex2num :: (Num a) = String - a
hex2num s = let (result, _):_ = readHex s in result
toEnv s = map tuple (split ';' s)
tuple :: String - (String, String)
tuple line = case split '=' line of
a:b:_ - (a,b)
a:_ - (a,)
_ - (,) -- not good, probably won't
happen for my typical usage...
split :: Char - String - [String]
split _ = []
split c s = let (l, s') = break (== c) s
in l : case s' of
[] - []
(_:s'') - split c s''
beginsWith [] [] = True
beginsWith _[] = True
beginsWith [] _ = False
beginsWith (a:aa) (b:bb)
| a == b = aa `beginsWith` bb
| otherwise= False
dropping [] [] = []
dropping [] _ = []
dropping x [] = x
dropping s@(a:aa) (b:bb) | a == b= dropping aa
bb
| otherwise = s
-- replace all occurrences of 'this' with 'that' in
the string 'str'
-- like Python replace
replace __[] = []
replace this that str
| str `beginsWith` this = let after = (str
`dropping` this)
in that ++ replace
this that after
| otherwise =
let x:xs = str
in x : replace this that xs
eat s = replace s
-- sometimes newlines get out of hand on the end of
form POST submissions,
-- so trim all the end newlines and add a single
newline
fixEndingNewlines = reverse . ('\n':) . dropWhile
(=='\n') . reverse .
filter (/= '\r')
endsWith a b = beginsWith (reverse a) (reverse b)
a `contains` b = any (`beginsWith` b) $ tails a
--
Jared.
On 6/12/06, Neil Mitchell [EMAIL PROTECTED]
wrote:
Hi,
I tend to use the module TextUtil (or Util.Text)
from Yhc for these
kind of string manipulations:
http://www-users.cs.york.ac.uk/~malcolm/cgi-bin/darcsweb.cgi?r=yhc;a=headblob;f=/src/compiler98/Util/Text.hs
separate = splitList ,
I am currently thinking about making this module
into a standalone
library with some other useful functions, if
people have any opinions
on this then please let me know.
Thanks
Neil
On 6/12/06, Sara Kenedy [EMAIL PROTECTED]
wrote:
Hi all,
I want to write a function to separate a string
into a list of strings
separated by commas.
Example:
separate :: String - [String]
separate Haskell, Haskell, and Haskell =
[Haskell, Haskell, and Haskell]
If anyone has some ideas, please share with me.
Thanks.
S.
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Re: Embedding newlines into a string? [Was: Re: [Haskell-cafe] Separate a string into a list of strings]
Hi On Mon, Apr 14, 2008 at 8:22 AM, Benjamin L. Russell [EMAIL PROTECTED] wrote: A friend and I were working on a Haskell version of Towers of Hanoi yesterday, and I tried writing out the program today, but got stuck on outputting newlines as part of the string; viz: | n == 1 = putStrLn (Move ++ show source ++ to ++ show dest ++ . ++ show '\n') show '\n' = \\n \n == \n Therefore: | n == 1 = putStrLn (Move ++ show source ++ to ++ show dest ++ . ++ \n) Note that you need the brackets, an in general don't call show on a String or a Char. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Separate a string into a list of strings
Hi all, I want to write a function to separate a string into a list of strings separated by commas. Example: separate :: String - [String] separate Haskell, Haskell, and Haskell = [Haskell, Haskell, and Haskell] If anyone has some ideas, please share with me. Thanks. S. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Separate a string into a list of strings
Off the top of my head:
separate :: String - [String]
separate [] = []
separate s =
case break (',' ==) s of
(s,[]) - [s]
(s,',':s') - s : separate s'
_ - error how did we get here?
There is at least one cunning rewriting with foldl, I think, but I
think this version is clearer.
/g
On 6/12/06, Sara Kenedy [EMAIL PROTECTED] wrote:
Hi all,
I want to write a function to separate a string into a list of strings
separated by commas.
Example:
separate :: String - [String]
separate Haskell, Haskell, and Haskell = [Haskell, Haskell, and Haskell]
If anyone has some ideas, please share with me. Thanks.
S.
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By sea-girls wreathed with seaweed red and brown
Till human voices wake us, and we drown.
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Re: [Haskell-cafe] Separate a string into a list of strings
Hi, I tend to use the module TextUtil (or Util.Text) from Yhc for these kind of string manipulations: http://www-users.cs.york.ac.uk/~malcolm/cgi-bin/darcsweb.cgi?r=yhc;a=headblob;f=/src/compiler98/Util/Text.hs separate = splitList , I am currently thinking about making this module into a standalone library with some other useful functions, if people have any opinions on this then please let me know. Thanks Neil On 6/12/06, Sara Kenedy [EMAIL PROTECTED] wrote: Hi all, I want to write a function to separate a string into a list of strings separated by commas. Example: separate :: String - [String] separate Haskell, Haskell, and Haskell = [Haskell, Haskell, and Haskell] If anyone has some ideas, please share with me. Thanks. S. ___ 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] Separate a string into a list of strings
Sara Kenedy wrote: Hi all, I want to write a function to separate a string into a list of strings separated by commas. Example: separate :: String - [String] separate "Haskell, Haskell, and Haskell" = ["Haskell", "Haskell", "and Haskell"] If anyone has some ideas, please share with me. Thanks. Here is a solution using the Posix regex module. Prelude Text.Regex splitRegex (mkRegex "[ \t]*,[ \t]*") "Haskell, Haskell, and Haskell" ["Haskell","Haskell","and Haskell"] This form should work regardless of locale, but appears to be broken, although I expect this is either my fault or that of the underlying Posix library: Prelude Text.Regex splitRegex (mkRegex "[:space:]*,[:space:]*") "Haskell, Haskell, and Haskell" ["Haskell"," Haskell"," and Haskell"] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Separate a string into a list of strings
Clifford Beshers wrote: Sara Kenedy wrote: Hi all, I want to write a function to separate a string into a list of strings separated by commas. Example: separate :: String - [String] separate Haskell, Haskell, and Haskell = [Haskell, Haskell, and Haskell] If anyone has some ideas, please share with me. Thanks. Here is a solution using the Posix regex module. Prelude Text.Regex splitRegex (mkRegex [ \t]*,[ \t]*) Haskell, Haskell, and Haskell [Haskell,Haskell,and Haskell] This form should work regardless of locale, but appears to be broken, although I expect this is either my fault or that of the underlying Posix library: Prelude Text.Regex splitRegex (mkRegex [:space:]*,[:space:]*) Haskell, Haskell, and Haskell [Haskell, Haskell, and Haskell] Going by man grep, those [:foo:] classes are only special inside a character class, otherwise [:space:]* = [aceps:]*. Prelude Text.Regex splitRegex (mkRegex [[:space:]]*,[[:space:]]*) Haskell, Haskell, and Haskell [Haskell,Haskell,and Haskell] Brandon ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Separate a string into a list of strings
Funny. I have a module called Useful.hs with some of these same sorts
of functions. (coming from Python where I used .split(',') and
.replace('\r', '') and such a lot):
--
module Useful where
import List ( intersperse, tails )
import Numeric ( readHex )
hex2num :: (Num a) = String - a
hex2num s = let (result, _):_ = readHex s in result
toEnv s = map tuple (split ';' s)
tuple :: String - (String, String)
tuple line = case split '=' line of
a:b:_ - (a,b)
a:_ - (a,)
_ - (,) -- not good, probably won't happen for my typical usage...
split :: Char - String - [String]
split _ = []
split c s = let (l, s') = break (== c) s
in l : case s' of
[] - []
(_:s'') - split c s''
beginsWith [] [] = True
beginsWith _[] = True
beginsWith [] _ = False
beginsWith (a:aa) (b:bb)
| a == b = aa `beginsWith` bb
| otherwise= False
dropping [] [] = []
dropping [] _ = []
dropping x [] = x
dropping s@(a:aa) (b:bb) | a == b= dropping aa bb
| otherwise = s
-- replace all occurrences of 'this' with 'that' in the string 'str'
-- like Python replace
replace __[] = []
replace this that str
| str `beginsWith` this = let after = (str `dropping` this)
in that ++ replace this that after
| otherwise =
let x:xs = str
in x : replace this that xs
eat s = replace s
-- sometimes newlines get out of hand on the end of form POST submissions,
-- so trim all the end newlines and add a single newline
fixEndingNewlines = reverse . ('\n':) . dropWhile (=='\n') . reverse .
filter (/= '\r')
endsWith a b = beginsWith (reverse a) (reverse b)
a `contains` b = any (`beginsWith` b) $ tails a
--
Jared.
On 6/12/06, Neil Mitchell [EMAIL PROTECTED] wrote:
Hi,
I tend to use the module TextUtil (or Util.Text) from Yhc for these
kind of string manipulations:
http://www-users.cs.york.ac.uk/~malcolm/cgi-bin/darcsweb.cgi?r=yhc;a=headblob;f=/src/compiler98/Util/Text.hs
separate = splitList ,
I am currently thinking about making this module into a standalone
library with some other useful functions, if people have any opinions
on this then please let me know.
Thanks
Neil
On 6/12/06, Sara Kenedy [EMAIL PROTECTED] wrote:
Hi all,
I want to write a function to separate a string into a list of strings
separated by commas.
Example:
separate :: String - [String]
separate Haskell, Haskell, and Haskell = [Haskell, Haskell, and
Haskell]
If anyone has some ideas, please share with me. Thanks.
S.
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--
http://www.updike.org/~jared/
reverse )-:
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Re: [Haskell-cafe] Separate a string into a list of strings
Hi beginsWith [] [] = True beginsWith _[] = True beginsWith [] _ = False beginsWith (a:aa) (b:bb) | a == b = aa `beginsWith` bb | otherwise= False I used to have this in my library then I discovered isPrefixOf :) (or flip isPrefixOf, I think in this case) endsWith a b = beginsWith (reverse a) (reverse b) ditto, isSuffixOf Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Separate a string into a list of strings
Brandon Moore wrote: Going by man grep, those [:foo:] classes are only special inside a character class, otherwise [:space:]* = [aceps:]*. Prelude Text.Regex splitRegex (mkRegex [[:space:]]*,[[:space:]]*) Haskell, Haskell, and Haskell [Haskell,Haskell,and Haskell] The smart money was on user error. Thanks. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
