[Ocaml-pxp-users] Problem with tree manipulation

[Gerd Stolpmann]

I'd suggest not to call create_element to create new elements, but use
the more official way of calling Pxp_document.create_element_node.

Typing of objects is notoriously difficult, especially when there are
optional arguments like for insert_nodes. Without checking this piece of
code in detail, it can easily happen that a single type hint solves your
problem, something like

(paragraph : _ Pxp_document.node)

or similar. 

Gerd

Am Donnerstag, den 30.07.2009, 13:18 -0700 schrieb Dario Teixeira:
> Hi,
> 
> I am getting type-checker errors on a simple function that manipulates a
> PXP document tree.  The function takes as parameter a 'parent' node and
> one of its children, named 'child'.  All it does is create a new element
> 'paragraph' whose parent is 'parent' and whose child is 'child' (the latter
> therefore gets a new parent).  In other words, the function transforms the
> hierarchy "parent -> child", into "parent -> paragraph -> child".  Its
> (simplified) code is as follows:
> 
> let foobar parent child =
> 	let paragraph = child#create_element child#dtd (T_element "p") []
> 	in	parent#insert_nodes ~pos:child#node_position [paragraph];
> 		child#remove ();
> 		paragraph#append_node child
> 
> The error is the following:
> 
> Error: This expression has type
>          'a Pxp_document.extension Pxp_document.node as 'a
>        but an expression was expected of type
>          < create_element : 'c ->
>                             Pxp_document.node_type ->
>                             'd list ->
>                             (< append_node : 'b -> unit; .. > as 'e);
>            data : Lambdoc_core.Basic.plain_t; dtd : 'c;
>            insert_nodes : pos:'f -> 'e list -> 'g; node_position : 'f;
>            node_type : Pxp_document.node_type;
>            optional_string_attribute : string -> string option;
>            position : 'h * int * 'i; remove : unit -> 'j;
>            required_string_attribute : string -> Lambdoc_core.Basic.raw_t;
>            sub_nodes : 'b list; .. >
>          as 'b
>        Types for method create_element are incompatible
> 
> 
> Now, it's my understanding that create_element essentially uses the given node
> as a template from which a new node is created (and I'm guessing I could have
> invoked it on 'parent' instead of 'child' with the same effect).  Also, the
> program type-checks as long as I don't invoke parent#insert_nodes.
> 
> Any thoughts on what I am doing wrong here?  (Many thanks in advance!)
> 
> Best regards,
> Dario Teixeira
> 
> 
> 
>       
> _______________________________________________
> Ocaml-pxp-users mailing list
> Ocaml-pxp-users at orcaware.com
> http://www.orcaware.com/mailman/listinfo/ocaml-pxp-users
> 
-- 
------------------------------------------------------------
Gerd Stolpmann, Bad Nauheimer Str.3, 64289 Darmstadt,Germany 
gerd at gerd-stolpmann.de          http://www.gerd-stolpmann.de
Phone: +49-6151-153855                  Fax: +49-6151-997714
------------------------------------------------------------