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Use Haskell for shell scripting

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Re: Use Haskell for shell scripting

#11

Post by knivets »

q3k wrote: post #10

I don't really see the point of this, apart from academic research values. POSIX shell is everywhere - your current Linux and OS X machines, old UNIX workstations, home routers, servers... Just drop in a file and it will probably run just fine, unless the author screwed something up completely. POSIX shell scripts are the perfect bootstrap mechanisms that will run almost anywhere regardless of architecture. Haskell,…

As far as I understand, you need interpreter only if you want to run file as a script, but if you compile beforehand, you can just use it, so no need for Haskell to be present in an operating system.

Re: Use Haskell for shell scripting

#12

Post by q3k »

knivets wrote: post #11
q3k wrote: post #10

I don't really see the point of this, apart from academic research values. POSIX shell is everywhere - your current Linux and OS X machines, old UNIX workstations, home routers, servers... Just drop in a file and it will probably run just fine, unless the author screwed something up completely. POSIX shell scripts are the perfect bootstrap mechanisms that will run almost anywhere regardless of architecture. Haskell,…

As far as I understand, you need interpreter only if you want to run file as a script, but if you compile beforehand, you can just use it, so no need for Haskell to be present in an operating system.

What's the point then? You just end up with opaque binary blobs that you have to first cross-compile to every possible OS and architecture... How is that scripting by any stretch of the definition?

Re: Use Haskell for shell scripting

#13

Post by boothead »

For all the considerable awesomeness that Gabriel produces, I always think the best part is the *.Tutorial module he includes. I always learn a lot and it's always a great over view that puts the work in context.

Everyone should do this!

Re: Use Haskell for shell scripting

#14

Post by S4M »

I don't know much about Haskell, but I thought it had some properties to isolate side effects, but the code he gives:

    main = do
        cd "/tmp"
        mkdir "test"
        output "test/foo" "Hello, world!"  -- Write "Hello, world!" to "test/foo"
        stdout (input "test/foo")          -- Stream "test/foo" to stdout
        rm "test/foo"
        rmdir "test"
        sleep 1
        die "Urk!"
Clearly doesn't (it creates a directory, writes in a file, removes that file and that directory all in one go without anything indicated by the function main. Is it because it's the main function of the program, or am I missing something?

Re: Use Haskell for shell scripting

#15

Post by nandemo »

dkarapetyan wrote: post #4

Who's the target audience of this exactly? I already see a language pragma, do notation, liftIO, parser combinators. Hamming has this great set of lectures on how he became a world renowned scientist and in one of the lectures he explains why Ada failed and other languages succeeded. The difference was that Ada was designed logically and most successful languages were designed psychologically. Even when government co…

Presumably the target is existing haskellers. Basically, "if you use Haskell, here's something to help you use it for shell scripts too".

I don't think it's reasonable to assert that Ada "failed" (e.g. it runs on large passenger airplanes), but in any case that's kinda beside the point, TFA isn't primarily about Haskell evangelism/advocacy.

> language pragma, do notation, liftIO, parser combinators.

Arguably, all of this is within the reach of an intermediate-level Haskell programmer. OverloadedStrings is considered a basic pragma.

Re: Use Haskell for shell scripting

#16

Post by comex »

q3k wrote: post #10

I don't really see the point of this, apart from academic research values. POSIX shell is everywhere - your current Linux and OS X machines, old UNIX workstations, home routers, servers... Just drop in a file and it will probably run just fine, unless the author screwed something up completely. POSIX shell scripts are the perfect bootstrap mechanisms that will run almost anywhere regardless of architecture. Haskell,…

Because shell is so deficient that even for "simple" things it is really easy to screw up - when whitespace or special characters in filenames cause some case you overlooked to screw up due to terrible quoting rules, when missing arguments cause [1], when you accidentally put bashisms in scripts labeled /bin/sh, when you suddenly have to do some basic text parsing (e.g. extracting capture groups from a regex) and have to either switch to perl or use some ugly bash extension that's incompatible between the version of bash OS X uses and the newer ones.

So you might want to use a different language - even for purely/mostly personal use, in which case Haskell would be fine.

[1] https://github.com/ValveSoftware/steam-for-linux/issues/3671

Re: Use Haskell for shell scripting

#17

Post by sbergot »

q3k wrote: post #10

I don't really see the point of this, apart from academic research values. POSIX shell is everywhere - your current Linux and OS X machines, old UNIX workstations, home routers, servers... Just drop in a file and it will probably run just fine, unless the author screwed something up completely. POSIX shell scripts are the perfect bootstrap mechanisms that will run almost anywhere regardless of architecture. Haskell,…

It is a bit easy to dismiss everything haskell related as only useful for "academic research". In fact I am not sure how do you make this link between this post and research at all.

Now if you don't know about haskell and want to write a quick and short lived script, there is 0 value in writing it in haskell. However, if you happen to now a bit of haskell and that your script is likely to be used several times you might find some benefits to this.

- haskell is quick to write and the code can be quite terse. You can create an myscript.hs file and run it with runhaskell. Zero platform complexity overhead.

- you get the benefits of static types which are easier maintenance and refactoring.

- if it evolves in anything more complex, it is easy to move it in a cabal project.

- if you need to do something cpu intensive, you can compile/profile/improve perfs.

Re: Use Haskell for shell scripting

#18

Post by sbergot »

S4M wrote: post #14

I don't know much about Haskell, but I thought it had some properties to isolate side effects, but the code he gives: main = do cd "/tmp" mkdir "test" output "test/foo" "Hello, world!" -- Write "Hello, world!" to "test/foo" stdout (input "test/foo") -- Stream "test/foo" to stdout rm "test/foo" rmdir "test" sleep 1 die "Urk!" Clearly doesn't (it creates a directory, writes in a file, removes that file and that directo…

You are right. In this case effects are not isolated. But in this particular script, there are no interesting things to move into a pure function. It does not mean that it wouldn't be the case in a more complex script.

Like everything, you have to learn to balance your IO code and your pure code. A bit like learning when to factor something into a separate class, or leave it in a few statement/methods. If you write everything in IO & do notation, you don't get the main benefits of haskell. But if your code is more than 10 lines long, chances are that there will be useful pure functions in it.

Re: Use Haskell for shell scripting

#19

Post by zoomerang »

S4M wrote: post #14

I don't know much about Haskell, but I thought it had some properties to isolate side effects, but the code he gives: main = do cd "/tmp" mkdir "test" output "test/foo" "Hello, world!" -- Write "Hello, world!" to "test/foo" stdout (input "test/foo") -- Stream "test/foo" to stdout rm "test/foo" rmdir "test" sleep 1 die "Urk!" Clearly doesn't (it creates a directory, writes in a file, removes that file and that directo…

Haskell functions return side-effects using the IO type, with the boilerplate plumbing being hidden with monads and do-notation. "main" in Haskell by default has a return type of "IO ()", and any "IO" values returned by that function are executed by the runtime.

The end result in this case is something that just looks and feels completely imperative.

but if you were to try and call, say, the "rmdir" function inside another function that didn't have an IO return type, you'd get a compile error. (More specifically, you could technically call the function, you just couldn't return the "IO" value as a result, so it couldn't perform any actions).

Re: Use Haskell for shell scripting

#20

Post by tome »

zoomerang wrote: post #19
S4M wrote: post #14

I don't know much about Haskell, but I thought it had some properties to isolate side effects, but the code he gives: main = do cd "/tmp" mkdir "test" output "test/foo" "Hello, world!" -- Write "Hello, world!" to "test/foo" stdout (input "test/foo") -- Stream "test/foo" to stdout rm "test/foo" rmdir "test" sleep 1 die "Urk!" Clearly doesn't (it creates a directory, writes in a file, removes that file and that directo…

Haskell functions return side-effects using the IO type, with the boilerplate plumbing being hidden with monads and do-notation. "main" in Haskell by default has a return type of "IO ()", and any "IO" values returned by that function are executed by the runtime. The end result in this case is something that just looks and feels completely imperative. but if you were to try and call, say, the "rmdir" function inside a…

> IO type

:)

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