[erlang-questions] List Question

Dmytro Lytovchenko <>
Mon Aug 7 14:27:04 CEST 2017


A string is a list of integers [$F, $T] (where $x is a code for the letter
x and so on)
A list of strings is a — List of lists of integers. That is [ [$F, $T],
[$S, $T] ]
So to check whether a value is a list of lists you take its first element
and check whether it's also a list

function([X | _] = List) when is_list(X) -> got a nonempty list of strings!
function([X | _]) when is_list(X) -> got a nonempty list of integers (one
string)
function([]) -> i am sorry, empty list is here

there is no way to know having an empty list what it supposed to contain.
So an empty list is an empty list

2017-08-07 14:13 GMT+02:00 Andrew McIntyre <>:

> Hello All,
>
> A Newbie question,
>
> Can I tell the difference Between a List of Strings and a Single
> String?
>
> eg the Value in a List may just be "FT" or it might be ["FT", "ST"]
>
> I do not know in advance if its a single string or a list of strings,
> but want to behave differently - actually return the first element of
> the list when there are multiple values. I have parsed a variable
> hierarchical structure and the hierarchy can vary over instances.
>
> As strings are lists "is_list" returns true for both. Is that soluble
> or do I need to change the data structure to indicate it. Sorry if
> this has obvious answer, but new to erlang.
>
> Thanks
>
> --
> Best regards,
> Andrew McIntyre                     mailto:
>
> sent from a real computer
>
> R&D Director
> Medical-Objects
> 4/102 Wises Road
> MAROOCHYDORE Q 4558
> AUSTRALIA
>
> www.medical-objects.com.au
>
>
> _______________________________________________
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> 
> http://erlang.org/mailman/listinfo/erlang-questions
>
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