Can I do var-assignment in a function?

[cnb]

extract(Str) ->
    A = string:tokens(Str," ").
    lists:sort(A).

I could of course do this:
lists:sort(string:tokens(Str," ")).

But lets say I want a bigger function that slo includes some deeper function calls, lets say 4-5
calls deep.

That's the main thing I dislike about functional programming, it is very expressive but sometimes it is hard afterwards to follow what a function does and it is hard hwen you have to read what is happening from right to the left.
It is easier to reason about when I can split into several calls.

I guess it is doable but I can't figure out the syntax.

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[Lev Walkin]

Circular Function wrote:

>   extract(Str) ->
>     A = string:tokens(Str," ").
>     lists:sort(A).
>
> I could of course do this:
> lists:sort(string:tokens(Str," ")).
>
> But lets say I want a bigger function that slo includes some deeper
> function calls, lets say 4-5
> calls deep.
>
> That's the main thing I dislike about functional programming, it is very
> expressive but sometimes it is hard afterwards to follow what a function
> does and it is hard hwen you have to read what is happening from right
> to the left.
> It is easier to reason about when I can split into several calls.
>
> I guess it is doable but I can't figure out the syntax.

Use comma.

extract(Str) ->
        A = string:tokens(Str," "),
        lists:sort(A).


That's it.

--
vlm
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[Philip Robinson-3]

You are almost there: you need to replace the period on the second
line with a comma.

extract(Str) ->
    A = string:tokens(Str, " "),
    lists:sort(A).

Generally speaking, sequential statements in a block are separated by
commas; blocks are separated by semi-colons; and functions are
terminated by a period.  Watch out for guards, though - commas and
semi-colons are used differently there.

Cheers,
Philip


2008/7/23 Circular Function <circularfunc@...>:

> extract(Str) ->
>     A = string:tokens(Str," ").
>     lists:sort(A).
>
> I could of course do this:
> lists:sort(string:tokens(Str," ")).
>
> But lets say I want a bigger function that slo includes some deeper function
> calls, lets say 4-5
> calls deep.
>
> That's the main thing I dislike about functional programming, it is very
> expressive but sometimes it is hard afterwards to follow what a function
> does and it is hard hwen you have to read what is happening from right to
> the left.
> It is easier to reason about when I can split into several calls.
>
> I guess it is doable but I can't figure out the syntax.
>
> ________________________________
> Sök efter kärleken!
> Hitta din tvillingsjäl på Yahoo! Dejting: http://se.meetic.yahoo.net
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> erlang-questions mailing list
> erlang-questions@...
> http://www.erlang.org/mailman/listinfo/erlang-questions
>

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[Roessner, Silvester]

Circular Function wrote:
>   extract(Str) ->
>     A = string:tokens(Str," ").
>     lists:sort(A).

I think the comma was just a typo and not the actual question. Am I right?

You want var-assignment because you want to write something like:

        extract(Str) ->
             A = string:tokens(Str," "),
             A = lists:sort(A),
             A = do_something_else(A),
             A = and_finalize(A).

But that doesn't work. You have to use a new variable each time.

        extract(Str) ->
             A1 = string:tokens(Str," "),
             A2 = lists:sort(A1),
             A3 = do_something_else(A2),
             A4 = and_finalize(A3).

Or this hard to read version

        extract(Str) ->
             A = and_finalize(do_something_else(lists:sort(string:tokens(Str," ")))).

This approach of functional languages has at least two big advantages:

        1. You don't accidentally overwrite variables
        2. You can see all results in the debugger.

And there should be no runtime penalty. Since the processor had to allocate and de-allocate the same amount of memory in each of the 3 cases -even if you don't see this in the code.

mit freundlichen Grüßen / with kind regards
 
Silvester Rößner
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[Joe Armstrong-2]

On Wed, Jul 23, 2008 at 3:29 PM, Roessner, Silvester
<silvester.roessner@...> wrote:

> Circular Function wrote:
>>   extract(Str) ->
>>     A = string:tokens(Str," ").
>>     lists:sort(A).
>
> I think the comma was just a typo and not the actual question. Am I right?
>
> You want var-assignment because you want to write something like:
>
>        extract(Str) ->
>             A = string:tokens(Str," "),
>             A = lists:sort(A),
>             A = do_something_else(A),
>             A = and_finalize(A).

extract(Str) ->
     Toks = string:tokens(Str, ""),
     SortedToks1 = lists:sort(Toks),
     ...

:-)

/J

>
> But that doesn't work. You have to use a new variable each time.
>
>        extract(Str) ->
>             A1 = string:tokens(Str," "),
>             A2 = lists:sort(A1),
>             A3 = do_something_else(A2),
>             A4 = and_finalize(A3).
>
> Or this hard to read version
>
>        extract(Str) ->
>             A = and_finalize(do_something_else(lists:sort(string:tokens(Str," ")))).
>
> This approach of functional languages has at least two big advantages:
>
>        1. You don't accidentally overwrite variables
>        2. You can see all results in the debugger.
>
> And there should be no runtime penalty. Since the processor had to allocate and de-allocate the same amount of memory in each of the 3 cases -even if you don't see this in the code.
>
> mit freundlichen Grüßen / with kind regards
>
> Silvester Rößner
> This message is intended for a particular addressee only and
> may contain business or company secrets. If you have received
> this email in error, please contact the sender and delete the
> message immediately. Any use of this email, including saving,
> publishing, copying, replication or forwarding of the message
> or the contents is not permitted.
>
> _______________________________________________
> erlang-questions mailing list
> erlang-questions@...
> http://www.erlang.org/mailman/listinfo/erlang-questions
>

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