Re: [Haskell-cafe] Re: new Haskell hacker seeking peer review

2005-02-23 Thread Andreas Farre 

Bjorn Bringert said:

 Or why not the two characters shorter, but much less readable:

 pointsFreeCat' = getArgs = mapM_ ((= putStr) . readFile)

 or maybe:

 pointsFreeCat'' = getArgs = mapM_ (putStr . readFile)

 (.) :: (b - IO c) - (a - IO b) - a - IO c
 (.) = (.) . flip (=)

 Is (.) in the standard libs? If not, should it be? I'm sure there is a
 shorter definition of (.) that I haven't thought of.

 /Bjorn

Or even:

k :: Monad m = (a - m b) - Kleisli m a b
k = Kleisli

runKleisli :: Monad m = Kleisli m a b - (a - m b)
runKleisli (Kleisli f) = f

cat :: IO ()
cat = getArgs = (runKleisli $ (k $ mapM readFile)  (k $ mapM_ putStr))

after noticing that (.) is pretty similar to () when we lift (a - IO
b) to (Kleisli IO a b). It is pretty disappointing that runKleisli isn't
defined so that I can be cool and completely point free too ;)

/Andreas

-- 
some cannot be created more equal than others

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Re: [Haskell-cafe] Re: new Haskell hacker seeking peer review

2005-02-22 Thread Bjorn Bringert 
Isaac Jones wrote:
John Goerzen [EMAIL PROTECTED] writes:
Here's an alternative:
module Main where
(snip john's version)
And what list would be complete without a points-free version.  It
doesn't operate on stdin, though like John's does:
pointsFreeCat :: IO ()
pointsFreeCat = getArgs = mapM readFile = putStrLn . concat
Or why not the two characters shorter, but much less readable:
pointsFreeCat' = getArgs = mapM_ ((= putStr) . readFile)
or maybe:
pointsFreeCat'' = getArgs = mapM_ (putStr . readFile)
(.) :: (b - IO c) - (a - IO b) - a - IO c
(.) = (.) . flip (=)
Is (.) in the standard libs? If not, should it be? I'm sure there is a 
shorter definition of (.) that I haven't thought of.

/Bjorn
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[Haskell-cafe] Re: new Haskell hacker seeking peer review

2005-02-18 Thread John Goerzen 
Here's an alternative:

module Main where

import System.IO
import System(getArgs)

catFile :: FilePath - IO ()
catFile fp = do contents - readFile fp
putStr contents

main :: IO ()
main = do hSetBuffering stdin (BlockBuffering Nothing)
  args - getArgs
  if not (null args)
 then mapM_ catFile args
 else do contents - getContents
 putStr contents

This avoids the whole EOF problem by using lazy I/O.  readFile and
getContents both return a String, but it's a lazy list; the contents of
the string are only generated on demand.  So this does not actually read
the entire file into memory as you might think at first glance.

Also, I added a hSetBuffering line.  Setting it to BlockBuffering can
improve performance.  LineBuffering could also be useful if people are
used to a certain type of interactive performance with cat.

-- John


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Re: [Haskell-cafe] Re: new Haskell hacker seeking peer review

2005-02-18 Thread Isaac Jones 
John Goerzen [EMAIL PROTECTED] writes:

 Here's an alternative:

 module Main where

(snip john's version)

And what list would be complete without a points-free version.  It
doesn't operate on stdin, though like John's does:

pointsFreeCat :: IO ()
pointsFreeCat = getArgs = mapM readFile = putStrLn . concat

-- And a regular version for reference

cat2 :: IO ()
cat2 = do a - getArgs
  lines - mapM readFile a
  putStrLn $ concat lines


peace,

  isaac
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Re: [Haskell-cafe] Re: new Haskell hacker seeking peer review

2005-02-18 Thread Dean Herington 
At 5:27 PM -0800 2/18/05, Isaac Jones wrote:
John Goerzen [EMAIL PROTECTED] writes:
 Here's an alternative:
 module Main where
(snip john's version)
And what list would be complete without a points-free version.  It
doesn't operate on stdin, though like John's does:
pointsFreeCat :: IO ()
pointsFreeCat = getArgs = mapM readFile = putStrLn . concat
-- And a regular version for reference
cat2 :: IO ()
cat2 = do a - getArgs
  lines - mapM readFile a
  putStrLn $ concat lines
peace,
  isaac
You probably want `putStr` instead of `putStrLn`, as the latter 
introduces a gratuitous newline at the end of the concatenated 
contents.

Dean
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