How to generalize executing a series of commands, based on a list?

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borked windows environment, want...

Peter Schmitz

17 Nov 2010 17 Nov '10

9:03 p.m.

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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Scott Turner

18 Nov 18 Nov

6:48 a.m.

On 2010-11-17 21:03, Peter Schmitz wrote:

...

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').

The 'sequence' function is handy for combining a series of actions, such as [system cmd1, system cmd2, ...].

...

I will also want to accumulate some results; probably just a failure count at this time.

'sequence' hangs on to the results. That may be what you need. For control over accumulating results the good stuff is in Data.Foldable.

...

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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Peter Schmitz

3:14 p.m.

Thank you very much for the help. -- Peter On Thu, Nov 18, 2010 at 4:48 AM, Scott Turner <1haskell@pkturner.org> wrote:

...

On 2010-11-17 21:03, Peter Schmitz wrote:

...
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').

The 'sequence' function is handy for combining a series of actions, such as [system cmd1, system cmd2, ...].

...
I will also want to accumulate some results; probably just a failure count at this time.

'sequence' hangs on to the results. That may be what you need. For control over accumulating results the good stuff is in Data.Foldable.

...
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

Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

steffen

7:40 a.m.

New subject: [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 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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Peter Schmitz

3:20 p.m.

New subject: 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 wrote:

...

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 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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Henk-Jan van Tuyl

5:44 p.m.

New subject: How to generalize executing a series of commands, based on a list?

On Thu, 18 Nov 2010 21:20:10 +0100, Peter Schmitz 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 --

Peter Schmitz

10:05 p.m.

New subject: 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 wrote:

...

On Thu, 18 Nov 2010 21:20:10 +0100, Peter Schmitz 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 --

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Henk-Jan van Tuyl
Peter Schmitz
Scott Turner
steffen