# [erlang-questions] why do I see a message about area of a square

Christopher Vance cjsvance@REDACTED
Mon Jan 26 08:30:22 CET 2015

```Even more technically, an Erlang "array" is a tuple containing a tree of
tuples.

On Mon, Jan 26, 2015 at 12:54 PM, Rick Pettit <rpettit@REDACTED> wrote:

> Technically Erlang does have arrays—see “erl -man array” for details.
>
> -Rick
>
> On Jan 25, 2015, at 4:42 PM, Christopher Vance <cjsvance@REDACTED> wrote:
>
> The argument is a tuple. Erlang does not have arrays; you have to decide
> whether to use a list or a tuple.
>
> On Mon, Jan 26, 2015 at 12:36 AM, Roelof Wobben <r.wobben@REDACTED> wrote:
>
>>  Nope, Thanks for the patience with me.
>>
>> So area is the function with 1 argument a array with the shape and the
>> parameters to calculate it.
>>
>> Roelof
>>
>>
>>
>> Hynek Vychodil schreef op 25-1-2015 om 14:23:
>>
>> Sorry, typo I mean area/1 and arity 1 because you have only one parameter.
>>
>> On Sun, Jan 25, 2015 at 1:24 PM, Roelof Wobben <r.wobben@REDACTED> wrote:
>>
>>>  Sorry, now im totally confused .
>>>
>>> where does the name array come from and why a arity 1 ?
>>>
>>> Roelof
>>>
>>>
>>> Hynek Vychodil schreef op 25-1-2015 om 13:07:
>>>
>>> Hi,
>>>
>>>  You don't have any functions named square, circle or triangle. You
>>> have only one function array/1 with four function clauses, the first for
>>> square, the second for circle, the third for triangle and the fourth
>>> catch-all one.
>>>
>>>  Hynek
>>>
>>> On Sun, Jan 25, 2015 at 12:29 PM, Roelof Wobben <r.wobben@REDACTED>
>>> wrote:
>>>
>>>> Thanks,
>>>>
>>>> That error messages disappear.
>>>>
>>>> As I understand it right. The eror message is on all functions so on
>>>> the square, circle and triangle functions.
>>>> And if not so, why also not a error functions on the other two.
>>>>
>>>> Roelof
>>>>
>>>>
>>>>
>>>>
>>>> Taavi Talvik schreef op 25-1-2015 om 12:22:
>>>>
>>>>  Until you export your functions, they remain local to
>>>>> module. And compiler sees here, that they are not used
>>>>> locally here.
>>>>>
>>>>> -export([area/1]).
>>>>>
>>>>> best regards,
>>>>> taavi
>>>>> On 25 Jan 2015, at 13:12, Roelof Wobben <r.wobben@REDACTED> wrote:
>>>>>
>>>>>  Hello,
>>>>>>
>>>>>> I have this programm  :
>>>>>>
>>>>>> -module(shapes).
>>>>>>
>>>>>> -import(math, [sqrt/1]).
>>>>>>
>>>>>> area({square, Side}) ->
>>>>>>    Side * Side ;
>>>>>>
>>>>>>
>>>>>> area({triangle, A, B, C}) ->
>>>>>>    S = (A + B + C)/2,
>>>>>>    math:sqrt(S*(S-A)*(S-B)*(S-C));
>>>>>>
>>>>>> area(Other) ->
>>>>>>    {error, invalid_object}.
>>>>>>
>>>>>>
>>>>>> As soon I as try to compile it , I see these messages :
>>>>>>
>>>>>>
>>>>>> 6> c(shapes).
>>>>>> shapes.erl:5: Warning: function area/1 is unused
>>>>>> shapes.erl:15: Warning: variable 'Other' is unused
>>>>>>
>>>>>> Why does Erlang do this?
>>>>>> On compile time you cannot see which functions are used and which not
>>>>>> in my oponion.
>>>>>>
>>>>>> Roelof
>>>>>>
>>>>>>
>>>>>> _______________________________________________
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>>>>>>
>>>>>
>>>>>
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>>>
>>>
>>>
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>>
>>
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>
>
> --
> Christopher Vance
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>
>

--
Christopher Vance
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