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