On Sat, Aug 14, 2010 at 10:39 PM, prad wrote:

here's one way:

import System (getArgs)

args <- getArgs

first = head args last  = last args and so on.

i can also do this

(first:last:z) <- getArgs

and avoid using head and tail. in fact, this seems nicer because i can pattern match for a specific series of inputs. however, if the inputs aren't there (eg say program arg1 only instead of program arg1 arg2), then the runtime pattern match failure error:

user error (Pattern match failure in do expression at Tests.hs:14:4-14)

is understandably generated. this of course doesn't happen if i just use args because there is no pattern matching.

is the former the better way to do it then? or are there other alternatives?

For really simple uses, you can always do something like:

getMyArgs :: IO (Maybe SomeDataTypeYouWant) getMyArgs = do args <- getArgs case args of [pattern, you, want] -> Just $ <parse arguments> _ -> Nothing

Then you can cleanly handle the 'Nothing' case and do whatever is appropriate for not having arguments. For more complicated cases, GHC ships with this module for processing command line arguments: http://haskell.org/ghc/docs/6.12.1/html/libraries/base-4.2.0.0/System-Consol... There are also a few packages on hackage: cmdargs, which is targeted towards programs with multiple operating modes which have different options: http://hackage.haskell.org/package/cmdargs parseargs: http://hackage.haskell.org/package/parseargs cmdlib is newer - I haven't seen a release announcement for it, so I don't know what sets it apart: http://hackage.haskell.org/package/cmdlib Antoine