[erlang-questions] How to return all records in dets

[Mark Nijhof]

Just a thought on commenting, but adding a disqus comment section to each
page might be a real quick way to enable that. Just add it to the templates
you use for generating the html. Later it should also be rather easy to
migrate them somewhere else if needed.

-Mark
 On Jun 1, 2014 11:09 AM, "Joe Armstrong" <erlang@REDACTED> wrote:

>
>
>
> On Sat, May 31, 2014 at 8:44 PM, <lloyd@REDACTED> wrote:
>
>> Hi Joe,
>>
>> I've resorted to approach 0 many times and much appreciate the generous
>> help I've received from the community. Indeed, response from the author of
>> my Erlang bible is particularly awesome. I hope one day to be competent
>> enough to play it forward.
>>
>> I also spend a great deal of time in the Erlang man pages. Problem is
>> that I'm one of those soft-headed liberal arts types. So, I often find the
>> man pages near incomprehensible (and not only Erlang). Yes, I perhaps
>> should have taken more math classes to grasp the elegant concision. But my
>> mind doesn't seem to be wired that way.
>>
>> I can't tell you how many times I've looked at the foldl/n docs and tried
>> to understand what the hell is going on. I get the general drift, but can't
>> bring it down to useful code. There's just too much inside-baseball.
>>
>> As a self-taught-from-books-and-web Erlang aspirant, I find concrete
>> examples and well-written tutorials most helpful. This gives me leverage to
>> apply your approach 3. In general, the concepts of Erlang are simple enough
>> once I grasp them. In fact, I marvel at the pragmatic elegance. Your books
>> provide particularly lucid explications. But the man pages? My how I wish I
>> had the time and chops to write a parallel set for noobies.
>>
>> Indeed, would it be helpful if I walked through and commented on the man
>> doc items that give me headaches?
>>
>
> Absolutely - There is a problem here - which I think should be addressed
> as soon as
> possible - "It is not easy to common and ask question about man pages" -
> I'd really like to see commenting in the style of the real world Haskell
> book.
>
> If you're interested take a look at
> http://book.realworldhaskell.org/read/types-and-functions.html - in
> particular look at how comments are added to the text.
>
> The erlang man pages are generated from XML so a commenting system should
> be
> easy to make.
>
> I'd like to see questions about the man pages discussed "inside the man
> pages"
> if you see what I mean - not "outside the man pages" (ie here)
>
> ...
>
> Folds are very common there are the "iterators with an accumulator"
>
> In an imperative language you might say
>
>     state = state0
>     for(i in x){
>         state = update(state, f(i))
>     }
>
> In erlang this is a fold
>
>     fold(F, State0, X)
>
> F is a function of I and State which returns a new state, and I iterates
> over the values in X
>
> so
>
>    fold(fun(I, S) -> I + S end, 0, L)
>
> is the same as
>
>     S = 0;
>     for(I in L){
>        S = S + I
>    }
>
> This is a very common programming pattern
>
> Cheers
>
> /Joe
>
>
>
>> Many thanks again for your kind help,
>>
>> Lloyd
>>
>> -----Original Message-----
>> From: "Joe Armstrong" <erlang@REDACTED>
>> Sent: Saturday, May 31, 2014 1:53pm
>> To: "Lloyd Prentice" <lloyd@REDACTED>
>> Cc: "Erlang-Questions Questions" <erlang-questions@REDACTED>
>> Subject: Re: [erlang-questions] How to return all records in dets
>>
>> The thing to Google for is "dets man erlang" - which should get you the
>> man
>> page
>> (even better is to store the man pages locally and do "erl -man dets")
>>
>> You want to "list" all records (I'm not sure what list means here - it
>> might mean
>> "print" or "make a list of").
>>
>> To make a list of all records you could say:
>>
>>    dets:foldl(fun(X, L) -> [X|L] end, [], Name)
>>
>> (Most collections - ie dets, ets, dict, etc. offer some kind of fold
>> operation that
>> traverses all objects in the collection)
>>
>> To print all records
>>
>>   dets:traverse(Name, fun(X) ->
>>                            io:format("~p~n",[X]),
>>                            continue
>>                       end)
>>
>> No need to worry about match specifications.
>>
>> The best place to start is usually by reading the man pages.
>>
>> Now that Erlang is is becoming popular you'll find a lot of incorrect
>> solutions to problems posted on stackoverlow.
>>
>> Best approach is
>>
>>     0) ask an expert
>>     1) read the man pages for the module, in question
>>     2) experiment with the functions in the man pages in the shell
>>     3) ask/tell this list if the manual pages are ambiguous or
>> incomprehensible
>>     4) search Google/stackoverflow
>>
>> Cheers
>>
>> /Joe
>>
>>
>>
>> On Fri, May 30, 2014 at 9:56 PM, <lloyd@REDACTED> wrote:
>>
>> > Hello,
>> >
>> > I'm cross-eyed from looking at match specifications. All I want to do is
>> > list all records in my small dets table. I once ran across a very neat
>> > query to accomplish that, but for the life can't Google it up.
>> >
>> > Can some kind soul give me a query that works?
>> >
>> > Many thanks,
>> >
>> > LRP
>> >
>> >
>> >
>> > _______________________________________________
>> > erlang-questions mailing list
>> > erlang-questions@REDACTED
>> > http://erlang.org/mailman/listinfo/erlang-questions
>> >
>>
>>
>>
>
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