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[Caml-list] how to define a property list
- Christoph Bauer
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Date: | 2004-04-23 (17:50) |
From: | Christoph Bauer <c_bauer@i...> |
Subject: | [Caml-list] how to define a property list |
Hi List, I want to create a tree. This tree should be a very simple accessible for algorithms and easy to understand. The nodes in the tree can have different properties of different types. An example of such a tree is the DOM-tree in JavaScript. There are several ways how to design such a tree. 1.) Using Records. Each node is a records, and the records contain a field for each possible property. Maybe a better approach is a type like this type ('a,'b) node = { <common fields>; mutable properties : 'a * 'b list } The list `properties' should be a key-value list. A Lisp-like alist would be perfect. Unfortunately the type 'b isn't fix. It can be string or int or something completely different. 2a) Using dynamic typing. type property_value = Int of int | String of String. type 'a node = { <common fields>; mutable properties : 'a * property_value list } If this is the solution, I'll better switch to Scheme, which has better support for dynamic types ;-) 2b) Add for each type a property list to node. type 'a node = { <common fields>; mutable int_properties : 'a * int list mutable string_properties : 'a * string list ... } This is my preferred solution so far. 3) Using OOP. (I'm not sure, whether OOP in general is good or bad.) class node = object end;; class ['a, 'b] sub_node a b= object(s) inherit node val mutable property1 : 'a = a ; val mutable property2 : 'b = b; method property1 = property1; method set_property1 = property1 method property2 = property2; method set_property2 = property2 end;; (* lot of typing for nothing so far*) let a = new sub_node 1 "a" :> node;; Question: How can I now access property1? Thanks for comments, Christoph Bauer -- beginfig(1)u=3cm;draw fullcircle scaled 2u;x0=x1=y1=x2=y3=0;-y0=y2=x3=1u; filldraw z0..{left}z1{left}..z2{curl 1}..z3..z0..cycle;def t(expr p)=fullcircle scaled .25u shifted(0,p*u);enddef;unfill t(.5);fill t(-.5);endfig;bye ------------------- To unsubscribe, mail caml-list-request@inria.fr Archives: http://caml.inria.fr Bug reports: http://caml.inria.fr/bin/caml-bugs FAQ: http://caml.inria.fr/FAQ/ Beginner's list: http://groups.yahoo.com/group/ocaml_beginners