Joachim Breitner

Haskell on the Command Line

Published 2006-07-24 in sections English, Haskell.

For all haskell-loving folks out they, consider these lines as an addon to your .bashrc:

    if which ghc >/dev/null
function hmap { ghc -e "interact ($*)"; }
function hmapl { hmap "unlines.($*).lines" ; }
function hmapw { hmapl "map (unwords.($*).words)" ; }

This is somewhat an replacement to "perl -e", for cases where haskell does the job nicer. So, you like triangular text files? Then try

cat /etc/passwd | hmapl zipWith take [1..]

In most cases, you want to run hmapl with map or filter as the first argument, e.g.

cat /etc/passwd | hmapl map reverse
w|hmapl 'filter (List.isPrefixOf "j")' # essentially grep ^j
man ghc|hmapw 'filter (all Char.isAlpha)'


discussed at
#1 Anonymous am 2007-03-02

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