Simple Unix tools: Difference between revisions
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This is intended as a beginners tutorial for learning Haskell from a | This is intended as a beginners tutorial for learning Haskell from a | ||
"Lets just solve things already!" point of view. | "Lets just solve things already!" point of view. The examples should | ||
help give a flavour of the beauty and expressiveness of Haskell | |||
programming. | |||
<haskell> | <haskell> | ||
| Line 22: | Line 24: | ||
-- The 'cat' program | -- The 'cat' program | ||
-- | -- | ||
cat | cat = input id | ||
-- | -- | ||
-- Sort a file | -- Sort a file | ||
-- | -- | ||
sort' = input sort | sort' = input sort | ||
-- | -- | ||
-- Reverse a file (tac) | -- Reverse a file (tac) | ||
-- | -- | ||
tac | tac = input reverse | ||
-- | -- | ||
-- Return the head -10 line of a file | -- Return the head -10 line of a file | ||
-- | -- | ||
head' = input $ take 10 | head' = input $ take 10 | ||
-- | -- | ||
-- Remove the first 10 lines of a file | -- Remove the first 10 lines of a file | ||
-- | -- | ||
drop' = input $ drop 10 | drop' = input $ drop 10 | ||
-- | -- | ||
-- Return the tail -1 line of a file | -- Return the tail -1 line of a file | ||
-- | -- | ||
tail' = input $ (:[]) . last | tail' = input $ (:[]) . last | ||
-- | -- | ||
-- remove duplicate lines from a file (like uniq) | -- remove duplicate lines from a file (like uniq) | ||
-- | -- | ||
uniq | uniq = input nub | ||
-- | -- | ||
-- double space a file | -- double space a file | ||
-- | -- | ||
space = input $ intersperse | space = input $ intersperse "" | ||
-- | -- | ||
-- repeat the input file infintely | -- repeat the input file infintely | ||
-- | -- | ||
rpt = interact cycle | |||
-- | -- | ||
| Line 87: | Line 89: | ||
-- Translate the letter 'e' to '*', like tr 'e' '*' (or y// in sed) | -- Translate the letter 'e' to '*', like tr 'e' '*' (or y// in sed) | ||
-- | -- | ||
y | y = interact $ map f | ||
where f 'e' = '*' | where f 'e' = '*' | ||
f c = c | f c = c | ||
| Line 93: | Line 95: | ||
-- Filter the letter 'e' from a file, like tr -d 'e' | -- Filter the letter 'e' from a file, like tr -d 'e' | ||
-- | -- | ||
tr | tr = interact $ filter (/= 'e') | ||
-- | -- | ||
-- Count number of characters in a file (like wc -c) | -- Count number of characters in a file (like wc -c) | ||
-- | -- | ||
wc_c | wc_c = interact $ show . length | ||
-- | -- | ||
-- Count number of lines in a file, like wc -l | -- Count number of lines in a file, like wc -l | ||
-- | -- | ||
wc_l | wc_l = interact $ show . length . lines | ||
-- | -- | ||
-- Count number of words in a file (like wc -w) | -- Count number of words in a file (like wc -w) | ||
-- | -- | ||
wc_w | wc_w = interact $ show . length . words | ||
-- | -- | ||
-- grep lines matching "^foo" from a file | -- grep lines matching "^foo" from a file | ||
-- | -- | ||
grep | grep = input $ filter (isPrefixOf "foo") | ||
-- | -- | ||
-- grep lines that don't match "^foo" (grep -v) | -- grep lines that don't match "^foo" (grep -v) | ||
-- | -- | ||
grep_v= input $ filter (not . isPrefixOf "foo") | grep_v = input $ filter (not . isPrefixOf "foo") | ||
-- | -- | ||
-- number each line of a file | -- number each line of a file | ||
-- | -- | ||
num | num = input $ zipWith ((. (' ':)) . shows) [1..] | ||
-- | -- | ||
-- Compute a simple cksum of a file | -- Compute a simple cksum of a file | ||
-- | -- | ||
main = interact $ printf "%u\n" . foldl' k 5381 | main = interact $ printf "%u\n" . foldl' k 5381 | ||
where k h c = h * 33 + fromIntegral (ord c) :: Int | where k h c = h * 33 + fromIntegral (ord c) :: Int | ||
</haskell> | </haskell> | ||
[[Category:Tutorials]] | [[Category:Tutorials]] | ||
Revision as of 06:54, 22 September 2006
Simple unix tools written in Haskell.
This is intended as a beginners tutorial for learning Haskell from a "Lets just solve things already!" point of view. The examples should help give a flavour of the beauty and expressiveness of Haskell programming.
--
-- Some unix-like tools written in elegant Haskell
--
import Data.List
import Data.Char
import System.IO
import Text.Printf
--
-- First, a useful helper
--
input f = interact (unlines . f . lines)
--
-- The 'cat' program
--
cat = input id
--
-- Sort a file
--
sort' = input sort
--
-- Reverse a file (tac)
--
tac = input reverse
--
-- Return the head -10 line of a file
--
head' = input $ take 10
--
-- Remove the first 10 lines of a file
--
drop' = input $ drop 10
--
-- Return the tail -1 line of a file
--
tail' = input $ (:[]) . last
--
-- remove duplicate lines from a file (like uniq)
--
uniq = input nub
--
-- double space a file
--
space = input $ intersperse ""
--
-- repeat the input file infintely
--
rpt = interact cycle
--
-- remove the first occurence of the line "str"
--
remove = input $ delete "str"
--
-- make a file all upper case
--
upper = interact $ map toUpper
--
-- remove leading space from each line
--
clean = input $ map (dropWhile isSpace)
--
-- join lines of a file
--
join = input $ (:[]) . concat
--
-- Translate the letter 'e' to '*', like tr 'e' '*' (or y// in sed)
--
y = interact $ map f
where f 'e' = '*'
f c = c
--
-- Filter the letter 'e' from a file, like tr -d 'e'
--
tr = interact $ filter (/= 'e')
--
-- Count number of characters in a file (like wc -c)
--
wc_c = interact $ show . length
--
-- Count number of lines in a file, like wc -l
--
wc_l = interact $ show . length . lines
--
-- Count number of words in a file (like wc -w)
--
wc_w = interact $ show . length . words
--
-- grep lines matching "^foo" from a file
--
grep = input $ filter (isPrefixOf "foo")
--
-- grep lines that don't match "^foo" (grep -v)
--
grep_v = input $ filter (not . isPrefixOf "foo")
--
-- number each line of a file
--
num = input $ zipWith ((. (' ':)) . shows) [1..]
--
-- Compute a simple cksum of a file
--
main = interact $ printf "%u\n" . foldl' k 5381
where k h c = h * 33 + fromIntegral (ord c) :: Int