[erlang-questions] suggestion: shorthand functions

Tue Jan 15 15:24:44 CET 2013

Hi Mahesh,

Sounds like Yuri's driver is distributed Erlang.

There are a bunch of apps out there that implement their command line
interfaces (CLI) as distributed Erlang nodes that spin up, interact
with another local node, then shut down. RabbitMQ does this.

I *hate* it! (anger issues)

- It's slow -- slower than *Java* for CLI operations

- It's brittle -- distributed Erlang can fail for a number of reasons
that are hard to diagnose

- It introduces a third OS process -- epmd, a little
single-point-of-failure devil that is the devil

I personally advocate run_erl, which exposes a shell to to_erl over
pipes. It's trivial to send commands to an Erlang process from bash or
Python or anything you like.

Some have criticized this approach as also being brittle. All I can
say is that I've used this for years across thousands of servers and
I'm very happy with it.

That said, I often spend my Sunday mornings over coffee wondering how
OS signal support isn't supported in Erlang.

Garrett

On Tue, Jan 15, 2013 at 7:46 AM, Mahesh Paolini-Subramanya
<mahesh@REDACTED> wrote:
> Ah, you misunderstand.
> I'm not running around saying Perl Now! Perl Forever!
> Instead, what we do is separate the problem domains (to the extent possible,
> of course).
> There is some set of functionality in the erlang application that needs to
> be exposed to our business processes - think "add a user", "disable a
> client", "add billing credits", etc.
> These are encapsulated and exposed via escript, and then embedded in perl
> via 'system' / 'qx' / backquotes / whatever.
> The same applies for activities like "rebalance node", "move user to debug
> node", etc. :-)
>
> cheers
> Mahesh Paolini-Subramanya
> That Tall Bald Indian Guy...
> Google+  | Blog   | Twitter  | LinkedIn
>
> On Jan 15, 2013, at 5:22 AM, Yurii Rashkovskii <yrashk@REDACTED> wrote:
>
> Mahesh,
>
> This is certainly a good point about bash/perl/python/whatever, but these
> become quite useless the moment you need to talk to some erlang node from
> your escript.
>
> Yurii.
>
> On Friday, January 11, 2013 7:11:26 AM UTC-8, Mahesh Paolini-Subramanya
> wrote:
>>
>> I love escripts but find myself intuitively avoiding them for a couple
>> reasons:
>>
>> - In most cases, bash is more portable and solves system level
>> problems more directly
>>
>> - I don't have the escript foo required to wrench my program it into a
>> single script file
>>
>>
>> Amen.
>> perl (bash, python, whatever) is optimally suited for orchestrating
>> between 'application space' and 'business space', as well as orchestration
>> across loosely coupled systems and activities.
>> Yes, you could force most of this into erlang-world, but to what point?
>> IMHO, we do live in a polyglot world, and we may as well take advantage of
>> it…
>>
>> Cheers
>>
>> p.s. Mind you, there is an entirely different argument to be made about
>> systems where you only have access to erlang (or Ada. or whatever :-)  )
>>
>> Mahesh Paolini-Subramanya
>> That Tall Bald Indian Guy...
>> Google+  | Blog   | Twitter  | LinkedIn
>>
>> On Jan 11, 2013, at 9:55 AM, Garrett Smith <g...@REDACTED> wrote:
>>
>> On Fri, Jan 11, 2013 at 8:18 AM, Raimo Niskanen
>> <raimo+erlan...@REDACTED> wrote:
>>
>> On Fri, Jan 11, 2013 at 10:12:40AM +0100, Ulf Wiger wrote:
>>
>> Since I've been writing a bunch of rebar.config.script code lately,
>> I've suffered the agony of trying to write concise and readable
>> code without having to do tons of copy-paste, weird unwrapping
>> funs etc.
>>
>> What I think would make this sort of thing easier, and also
>> escript programming in general, is if OTP could provide some
>> modules with concise naming and let-it-fail semantics.
>>
>> Just off the top of my head, I scribbled down a few functions that
>> I think would make *my* life easier. I pushed them to github to
>> get some discussion going.
>>
>> http://github.com/uwiger/shorthand
>>
>> The modules are:
>>
>> f.erl - shorthand functions for file.erl
>> fn.erl - ditto for filename.erl
>> e.erl - ditto for erl_eval.erl
>>
>> The least beneficial is perhaps filename:erl, but my fingers and
>> eyes ache from all the filename:join(filename:dirname(F), …)
>> code.
>>
>> Otherwise, I think the biggest benefit is to stick to let-it-crash
>> programming, which I find is usually the default when I write
>> scripts. The original functions are always available if you want
>> to take a closer look at return values.
>>
>> (For the file:script() counterparts, I also always pass the name
>> of the script as a binding).
>>
>> Comments?
>>
>>
>> I think it is a nice idea that would improve scripting.
>>
>> But how to agree on module names and content is harder. There is a limited
>> number of 1 and 2 character module names, and once in OTP they are written
>> in stone.
>>
>>
>> Aye. I don't know how critical this use case is (scripting
>> simplification/improvements) to justify new modules in OTP space. And
>> I'm not sure there *is* a case that would be sufficiently ubiquitous.
>>
>> I've resigned myself to writing little project specific
>> functions/libraries like this to deal with project specific problems.
>> E.g. this stuff drives me nuts:
>>
>> {ok, X} = foo:x(),
>> {ok, Y} = foo:y(),
>> combine(X, Y)
>> ...
>>
>> So I'll write foo_x/0 and foo_y/0 with crash-on-error semantics to get
>> this:
>>
>> combine(foo_x(), foo_y())
>>
>> But who knew that I needed those particular variants? And what about
>> changes? It's my project, so I don't mind little wrappers, especially
>> since functions clarify intent.
>>
>> E.g. when I see this:
>>
>> ProjectFile = filename:join(ProjectDir, ProjectName)
>>
>> I'll almost create a function like this:
>>
>> project_filename(Dir, Name) -> filename:join(Dir, Name).
>>
>> For f.erl I miss e.g is_dir from filelib, which would introduce the notion
>> of merging old module functionality. Using the name 'fl' for filelib
>> functions would just be hard to remember.
>>
>> Aliasing filename:basename to fn:base is a bit unintuitive since the
>> original Unix command is called 'basename' and for e.g file:list_dir
>> you have aliased it to f:ls (as for many other) to make them more
>> Unix:ish.
>> I think it would be better to keep to unix command names where possible.
>> [Wild idea: f:'-d' for filelib:is_dir, or t:'-d', or f:test(d, Path).]
>>
>>
>> It seems one could make these arguments ad nauseam. To me it's just
>> easier (and preferable frankly) to roll my own as the need arises.
>>
>> An alternative approach might be to have a helper module named 'es'
>> containing all scripting aliases...
>>
>>
>> I love escripts but find myself intuitively avoiding them for a couple
>> reasons:
>>
>> - In most cases, bash is more portable and solves system level
>> problems more directly
>>
>> - I don't have the escript foo required to wrench my program it into a
>> single script file
>>
>> Setting bash aside (not Ulf's use case) the main barrier for me is in
>> the perceived complexity of getting a release-of-sorts into an
>> escript. If I could write up one of these wrapper libraries, or pull
>> it down from somewhere easily, I might use escript everywhere. It's
>> not hard to write the wrappers (you write them as you need them, it
>> takes literally less than a minute for each function) and they're
>> tailored to your requirements.
>>
>> It may be trivial to package up the required bytes into an escript
>> today. If it is, I've love to know!
>>
>> And I don't know how this fits into rebar specific scripting :)
>>
>> Garrett
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