Arc Forumnew | comments | leaders | submitlogin
How to pass a type symbol into a function expecting a table ?
1 point by thaddeus 5840 days ago | 10 comments
BTW: I hope everyone had a good Christmas!!!!

So, I have this function that takes the name of a table as an argument:

    (def thad (table-name)
       (some table function using table-name))
The table is created upstream with a name derived from 'uniq' then passed around as table-name.

I am then storing this uniq-table-name as an element in another table: temp-table.

My problem now is that I am trying to take the uniq-table-name element from the temp-table and pass it into Thad, only it's now a type symbol and so dies a horrible death....

    Arc > ((temp-table 0) 1)
    QYVSn5n1
    ; QYVSn5n1 is the table-name

    Arc > (eval (thad QYVSn5n1))
    ; this works... 

    Arc > (eval (thad ((temp-table 0) 1)))
    Error: "Function call on inappropriate object


    
I've played around with 'apply', 'compose', 'ssexpand', but it's not working for me.

Any suggestions?, no need to write code for me, even just point me in the right direction. Thanks. T.



3 points by eds 5840 days ago | link

Let me see if I understand your question.

  >    Arc > (eval (thad QYVSn5n1))
  >    ; this works... 
This works because you are evaluating the symbol QYVSn5n1 for it's value (whatever that happens to be).

Actually (if I understand your code correctly), you don't need the call to 'eval here, since everything put into the REPL already gets evaluated.

  >    Arc > (eval (thad ((temp-table 0) 1)))
  >    Error: "Function call on inappropriate object
This doesn't work because ((temp-table 0) 1) evaluates to the symbol QYVSn5n1, and then passes the symbol itself (not the value of the symbol) to 'thad. If 'thad expects something other than a symbol, this blows up.

If you want to get the value of symbol instead, try using 'eval on the symbol.

  arc> (= tab (table))
  #hash()
  arc> (= (tab 'foo) 'bar)
  bar
  arc> (= bar [prn "Hello, " _])
  #<procedure: bar>
  arc> (tab 'foo)
  bar
  arc> (eval (tab 'foo))
  #<procedure: bar>
  arc> ((eval (tab 'foo)) "world")
  Hello, world
  "Hello, "
Of course, if 'thad is really supposed to take a symbol rather than a table directly, you'll need to move the calls to eval inside 'thad.

(I'm curious: why do you need to use symbols here instead of just passing tables to 'thad?)

-----

1 point by thaddeus 5840 days ago | link

ah, I think I see how it can be done... I could bind the uniq-table-name to the symbol of the key. .... makes sense (I think) :).

I hadn't thought of this option because I had been storing the order number in the key position and wouldn't have been able to bind anything to a number like '0'. I was doing this because; calling the table using any table function that return all entries, does not return the order as it was stored, but rather it seems to return them randomly (and the order stored was not sortable). ex. (temp-table) or (vals temp-table).

I hope that made sense.

As for the other question(s),I'll try not to overwhelm....

I'm letting users upload one or many spreadsheets of their choice.... so I then store into a newly generated table which in turn generates html table(s) accessible using their web session. After they close out the web session there's no need to store the data since it will write it back out to a new spreadsheet an store it locally for them. Since I am re-using these functions, i've made them generic, but if they refresh the webpage the html-table functions needs to re-run passing in the correct table-names...so I keep track of which tables had been created for re-loading, hence the storing of the table names as symbols in a table.

I doubt that made sense, but it's what i could muster after 6 hours in front of this code :)

Thanks. T.

As a note my table contained more than just a pair, each entry in the temp-table was storing: order, value, type

-----

3 points by CatDancer 5839 days ago | link

calling the table using any table function that return all entries, does not return the order as it was stored, but rather it seems to return them randomly

Yes, if you need to keep track of things in a particular order (such as the order you added them), you should put them in a list.

Note that you can put the same data in both a list and in a table, if that is what you need for your application.

hence the storing of the table names as symbols in a table

If you want to have a mapping of table names to tables, you can store that in its own table:

  (= tables* (table))
  (= tables*!QYVSn5n1 my-data-table-1)
  (= tables*!UYg47nnb my-data-table-2)
then to get at a particular table

  (let table-name 'UYg47nnb
    (let data-table (tables* table-name)
      ... (vals data-table) etc. ...

-----

1 point by thaddeus 5839 days ago | link

Great! That worked for me.... Not sure why I didn't think of it, but hey I've only been programming for a month now :) Thanks for everyone's help. T.

    (= my-data-table-1 (table))
    (= (my-data-table-1 'drink) 'milk)
    (= (my-data-table-1 'eat) 'eggs)

    arc> (keys my-data-table-1)
    (drink eat)
    arc> (vals my-data-table-1)
    (milk eggs)

    (= my-data-table-2 (table))
    (= (my-data-table-2 'run) 'fast)
    (= (my-data-table-2 'walk) 'slow)

    arc>(keys my-data-table-2)
    (walk run)
    arc>(vals my-data-table-2)
    (slow fast)

    (= tables* (table))
    (= (tables* '0) my-data-table-1)
    (= (tables* '1) my-data-table-2)

    (def load-ordered-tables ()
      (for i 0 (- (len tables*) 1)
        (let current-table (tables* i)
          (pr (vals current-table))
     )
      ))
	

    arc> (load-ordered-tables)
    (milk eggs)(slow fast)nil

-----

1 point by CatDancer 5839 days ago | link

You're welcome!

If it turns out that you just need a list of your data tables, you can do this:

  (= tables* (list my-data-table-1 my-data-table-2))

  (def load-ordered-tables ()
    (each current-table tables*
      (pr (vals current-table))))

-----

1 point by thaddeus 5839 days ago | link

and ..Hey go figure..... I even figured out how to make it work the way I was originally attempting to make it work ! :)

    arc> temp-table
    #hash((0 . (0 hUv086uP)) (1 . (1 CH3w2sdp)))
    
    arc> ((temp-table 1) 1)
    CH3w2sdp

    (= CH3w2sdp (table))
    (= (CH3w2sdp 'run) 'fast)
    (= (CH3w2sdp 'walk) 'slow)

    (def thad ()
       (eval `(vals ,((temp-table 1) 1))))

     arc>(thad)
     (slow fast)
T.

-----

1 point by lboard 5811 days ago | link

Thanks

-----

1 point by thaddeus 5840 days ago | link

ugh - ok that didn't work after all.

The example:

    (= bar [prn "Hello, " _])
worked for you as it did not contain a table function requiring a table name passed in.

so I'm still stumpfied :) lol.

-----

1 point by cchooper 5840 days ago | link

@thaddeus

I'm not sure I understand what you're doing, but perhaps you need another table that maps the symbols you created to the tables they refer to. Call it table-names. Then you could rewrite thad like this:

  (def thad (table-or-table-name)
    (if (isa table-or-table-name 'table) (do-what-you-did-before)
        (thad (table-names table-or-table-name))))
But I suspect there is a better way of doing what you're trying to do, so if you give us some more details then we might be able to suggest a more sane alternative.

-----

1 point by CatDancer 5840 days ago | link

Can you just use symbols as names and not use eval at all? If not, what is your overall goal that you want to accomplish?

-----