a question bout exetract a sub-element of element in triple

a question bout exetract a sub-element of element in triple

[Su Zhang]

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I encountered a new problem which is I want to get " 1 " from a triple
"(0,2,[1,2,3])", which means I want to get the first value of the third item
in one triple and itself is a list, but when I use the List.hd
(third(0,2,[1,2,3])), it will give me the entire list which is [1,2,3]
the definition of the third is "let third(x,y,z)=z", so is there a way I can
get out "1" from "(0,2,[1,2,3])"? if possible, would you please give me some
advices?

thank you very much

-- 
Su Zhang

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Re: [Caml-list] a question bout exetract a sub-element of element in triple

[Christophe Raffalli]

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Su Zhang a écrit :
> I encountered a new problem which is I want to get " 1 " from a triple
> "(0,2,[1,2,3])", which means I want to get the first value of the
> third item in one triple and itself is a list, but when I use the
> List.hd (third(0,2,[1,2,3])), it will give me the entire list which is
> [1,2,3]
> the definition of the third is "let third(x,y,z)=z", so is there a way
> I can get out "1" from "(0,2,[1,2,3])"? if possible, would you please
> give me some advices?
>  
> thank you very much
List.hd (third(0,2,[1;2;3])) ?

[1,2,3], is a one element list ...

Cheers,
Christophe

>
> -- 
> Su Zhang
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-- 
Christophe Raffalli
Universite de Savoie
Batiment Le Chablais, bureau 21
73376 Le Bourget-du-Lac Cedex

tel: (33) 4 79 75 81 03
fax: (33) 4 79 75 87 42
mail: Christophe.Raffalli@univ-savoie.fr
www: http://www.lama.univ-savoie.fr/~RAFFALLI
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Re: [Caml-list] a question bout exetract a sub-element of element in triple

[Florent Ouchet]

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Su Zhang a écrit :
> I encountered a new problem which is I want to get " 1 " from a triple 
> "(0,2,[1,2,3])", which means I want to get the first value of the 
> third item in one triple and itself is a list, but when I use the 
> List.hd (third(0,2,[1,2,3])), it will give me the entire list which is 
> [1,2,3]
> the definition of the third is "let third(x,y,z)=z", so is there a way 
> I can get out "1" from "(0,2,[1,2,3])"? if possible, would you please 
> give me some advices?
Hi,

[1,2,3] is equivalent to [(1,2,3)], which means "a list containing one 
element whose type is (int*int*int)".
first (List.hd (third(0,2,[1,2,3]))) = 1

[1;2;3] denotes a list of three integer elements.
List.hd (third(0,2,[1;2;3])) = 1

As said in a reply to your previous message, you'll get more complete 
answers by posting to this more suited group: 
http://groups.yahoo.com/group/ocaml_beginners

Cheers,

Florent


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