------------------------------------------------------------------------
h4sh
------------------------------------------------------------------------
Requirements:
> make (GNU or BSD)
> The Glasgow Haskell Compiler
> Cabal
> hs-plugins:
darcs get http://www.cse.unsw.edu.au/~dons/code/hs-plugins
> fps 0.5:
darcs get http://www.cse.unsw.edu.au/~dons/code/fps
Building:
> PREFIX=/tmp make
> make install
also
> make check (you may need to adjust the variable `GM4' in the
toplevel Makefile, or in the environment)
------------------------------------------------------------------------
Manifesto:
Unix is all about programs that do one thing, and one thing well.
Unfortunately, over time, the common unix text processing commands have
become bloated and silly, with rather arbitrary features for programs
that should have simple semantics (consider uniq and wc outputting
leading space, or cut indexing fields from 1).
On the other hand Haskell has a powerful and beautiful List library for
processing text. By exposing the Haskell List library as a set of shell
utilities, and utlising function composition via pipes, we can program
in the shell using these precise, clean Haskell functions.
To this end, h4sh makes the functions of this library available as unix
shell commands.
For example:
take 100 data | map show.length | sort | reverse | head
Commands are generated from a description of their type. h4sh utilities
thus have standard behaviour, for example, all functions read from stdin
or file arguments (meaning that `id' is equivalent `cat'), and arguments
are handled in the order they appear in the function type signature.
h4sh currently compiles functions of the following types:
a -> a
a -> [a]
[a] -> a
[a] -> Int
[a] -> [a]
[[a]] -> [a]
a -> [a] -> [a]
a -> [a] -> [Int]
Int -> [a] -> [a]
[a] -> [a] -> [a]
(a -> a) -> a -> a
(a -> a) -> a -> [a]
(a -> a) -> [a] -> [a]
(a -> a) -> [a] -> a
(a -> Bool) -> [a] -> [a]
(a -> a -> a) -> [a] -> a
(a -> Maybe (a, a)) -> a -> [a]
The following functions are provided as shell commands:
(!!) ($) (++) (:) (\\)
concat concatMap cycle
delete drop dropWhile
elemIndices filter foldl
foldr group head id init
insert intersect intersperse
iterate last length map
maximum minimum nub repeat
reverse show sort tail
take takeWhile transpose
unfoldr union words zip
Higher order functions like map are handled using runtime evaluation,
provided by the hs-plugins library, allowing arbitrary Haskell code to
be evaluated, e.g. for map and filter.
h4sh also provides a library H4SH.List of useful String and Regex
functions.
h4sh was written during a cold, but sunny weekend in August 2005.