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Date: | 2004-08-23 (05:13) |
From: | Michael Alexander Hamburg <hamburg@f...> |
Subject: | [Caml-list] camlp4 and class values |
I'm trying to write a simple game in ocaml, largely to give me an excuse to learn more of the language. To deal with rule-changing effects, a large fraction of the methods in the game will have to be more or less mutable, although they will be mutated in a specific, nontrival way. I've created a module, temporarily called Stack, which implements the kind of mutation I want, so now there's the issue of define the methods. For now, the implementation goes thusly: class test = object (self) val onFoo : (test -> int -> int) Stack.t = Stack.create (fun _ _ -> 0) method foo x = Stack.apply onFoo self x method addFoo f = Stack.append onFoo f end And this sort of thing works, but it would be nice if I didn't have to write these three things for all the extensible methods, which is quite a lot of methods. So I've been trying to write a camlp4 preprocessor, which would take class test = object (self) extmethod foo (x:int) = 0 end or the like, and turn it into the above code. I haven't been able to get anything to work, though. I don't really know camlp4, although not for lack of trying (I've spent several hours working through its documentation). The best I've been able to do is something like: #load "pa_extend.cmo";; #load "q_MLast.cmo";; open Pcaml open MLast let addName n = "add_" ^ n let onName n = "on_" ^ n let o2b = function Some _ -> true | None -> false let genfunc loc params e = <:expr< Stack.apply (fun self $params$ -> $e$) >> let genval loc l params e = <:class_str_item< value $lid:onName l$ = $genfunc loc params e$ >> let genmeth loc pf l topt params = <:class_str_item< method $opt:o2b pf$ $l$ $opt:topt$ $patt:params$ = Stack.apply $lid:onName l$ self $params$>> let genadd loc pf l = <:class_str_item< method $opt:o2b pf$ $addName l$ f = Stack.append $lid:onName l$ f >> EXTEND class_str_item : LAST [[ "extmethod"; pf = OPT "private"; l = LIDENT; topt = OPT ctyp; params = LIST0 patt; "="; e = expr -> let meth = genmeth loc pf l topt params and add = genadd loc pf l and v = genval loc l params e in <:class_str_item< declare $v$; $meth$; $add$; end >> ]]; END;; which raises: File "extmethod.ml", line 22, characters 52-65: While expanding quotation "class_str_item": Parse error: [fun_binding] expected (in [class structure item]) Uncaught exception: Pcaml.Qerror("class_str_item", 1, _) Preprocessor error The closest thing I've been able to find to documentation on fun_bindings is the camlp4 source, which does a much more direct translation. How do I write such an extenision? OR is there some reason that it's not possible? Thanks for your time, Mike Hamburg ------------------- 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