[Haskell-cafe] Re: How to generalize executing a series of commands, based on a list?
1. Write one routine, which does all the work for just one command.
2. use sequence or mapM, mapM_ from Control.Monad (depending on your
needs),
to apply your function to a list of commands
accumulating results you may want to process the output of sequence
or use the WriterT Monad Transformer.
If you want to stop processing the rest of the list on error, either
write a recursive function yourself or use foldM or use ErrorT Monad
Transformer.
On Nov 18, 3:03 am, Peter Schmitz ps.hask...@gmail.com wrote:
I am able to use System.Cmd (system) to invoke a shell command
and interpret the results.
Please see the code below that works okay for one such command.
(I invoke a program, passing two args.)
I am wondering how to generalize this to do likewise for a
series of commands, where the varying args (filenames, in this
case) are in a list ('inOutLeafs').
I will also want to accumulate some results; probably just a
failure count at this time.
Any advice or pointers to examples would be much appreciated.
Thanks in advance,
-- Peter
run :: ... - IO (Int) -- will return a fail count
run
-- some args to this function here...
= do
-- ... set up: inputLeafs, outputLeafs, etc.
-- zip two lists of filenames:
let inOutLeafs = zip inputLeafs outputLeafs
-- the first pair for the first command:
let (inFile1,outFile1) = head inOutLeafs
-- build 1st command using 1st pair of filenames:
let cmd1 = ...
exitCode - system cmd1
case (exitCode) of
ExitSuccess - do
putStrLn $ -- OK.
return 0
ExitFailure failCnt - do
putStrLn $ -- Failed: ++ show failCnt
return 1
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Re: [Haskell-cafe] Re: How to generalize executing a series of commands, based on a list?
Thank you very much for the help. Good tips for improving my code design.
I'm new to sequence, mapM, and mapM_; I've seen mapM a lot while reading
code and wanted to learn it; now I have a reason! Thanks.
-- Peter
On Thu, Nov 18, 2010 at 5:40 AM, steffen steffen.sier...@googlemail.comwrote:
1. Write one routine, which does all the work for just one command.
2. use sequence or mapM, mapM_ from Control.Monad (depending on your
needs),
to apply your function to a list of commands
accumulating results you may want to process the output of sequence
or use the WriterT Monad Transformer.
If you want to stop processing the rest of the list on error, either
write a recursive function yourself or use foldM or use ErrorT Monad
Transformer.
On Nov 18, 3:03 am, Peter Schmitz ps.hask...@gmail.com wrote:
I am able to use System.Cmd (system) to invoke a shell command
and interpret the results.
Please see the code below that works okay for one such command.
(I invoke a program, passing two args.)
I am wondering how to generalize this to do likewise for a
series of commands, where the varying args (filenames, in this
case) are in a list ('inOutLeafs').
I will also want to accumulate some results; probably just a
failure count at this time.
Any advice or pointers to examples would be much appreciated.
Thanks in advance,
-- Peter
run :: ... - IO (Int)-- will return a fail count
run
-- some args to this function here...
= do
-- ... set up: inputLeafs, outputLeafs, etc.
-- zip two lists of filenames:
let inOutLeafs = zip inputLeafs outputLeafs
-- the first pair for the first command:
let (inFile1,outFile1) = head inOutLeafs
-- build 1st command using 1st pair of filenames:
let cmd1 = ...
exitCode - system cmd1
case (exitCode) of
ExitSuccess - do
putStrLn $ -- OK.
return 0
ExitFailure failCnt - do
putStrLn $ -- Failed: ++ show failCnt
return 1
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Re: [Haskell-cafe] Re: How to generalize executing a series of commands, based on a list?
On Thu, 18 Nov 2010 21:20:10 +0100, Peter Schmitz ps.hask...@gmail.com wrote: Thank you very much for the help. Good tips for improving my code design. I'm new to sequence, mapM, and mapM_; I've seen mapM a lot while reading code and wanted to learn it; now I have a reason! Thanks. -- Peter You can find explanations, with usage examples, of these functions at http://members.chello.nl/hjgtuyl/tourdemonad.html Regards, Henk-Jan van Tuyl -- http://Van.Tuyl.eu/ http://members.chello.nl/hjgtuyl/tourdemonad.html -- ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: How to generalize executing a series of commands, based on a list?
Thanks very much for the url; helpful site. I got mapM to do what I wanted (first time I've used it); cool function; now I understand it. At your note for mapM I noticed (mapM print); I've been using (show [list]) so much, (mapM print) will be nice for formatting while debugging, etc. Thanks again! -- Peter On Thu, Nov 18, 2010 at 3:44 PM, Henk-Jan van Tuyl hjgt...@chello.nlwrote: On Thu, 18 Nov 2010 21:20:10 +0100, Peter Schmitz ps.hask...@gmail.com wrote: Thank you very much for the help. Good tips for improving my code design. I'm new to sequence, mapM, and mapM_; I've seen mapM a lot while reading code and wanted to learn it; now I have a reason! Thanks. -- Peter You can find explanations, with usage examples, of these functions at http://members.chello.nl/hjgtuyl/tourdemonad.html Regards, Henk-Jan van Tuyl -- http://Van.Tuyl.eu/ http://van.tuyl.eu/ http://members.chello.nl/hjgtuyl/tourdemonad.html -- ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
