camlp4 & free variables
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Date:   (:) 
From:  Nicolas Pouillard <nicolas.pouillard@i...> 
Subject:  Re: [Camllist] camlp4 & free variables 
On 7/20/06, Christophe TROESTLER <Christophe.Troestler@umh.ac.be> wrote: > On Thu, 20 Jul 2006, "Nicolas Pouillard" <nicolas.pouillard@gmail.com> wrote: > > > > On 7/20/06, Christophe TROESTLER <Christophe.Troestler@umh.ac.be> wrote: > > > Hi, > > > > > > Is it possible to write a camlp4 syntax extension that "extract" the > > > free variables of an expression? > > You are quite lucky, the camlp4 version has one module to do that! > > Thank you very much for your help! Is there an updated manual for > camlp4 (if possible written more from a user perspective :)? > Alas not now. > If I understand well your code (I really ought to learn camlp4!) > FV.free_vars first argument is a set of names which should net be > considered as free variables. Is it possible to do it contextually, > e.g. in > > open_out("X" ^ x) > > only "x" is returned as free because "open_out" and "^" are known from > Pervasives? Or in > > let z = 1 > ... > FUNCTION(x + z) > > only "x" is returned as free because "z" is known from the context? > In my previous program, I provide a function f that takes an AST: f <<let z = x + 2 in x + 2 * y * x * z>> Here the AST is given using a quotation but there is no relation between the code outside and inside the quotation so: let x = 42 in f <<let z = x + 2 in x + 2 * y * x * z>> This code does not bind x inside the quotation. Now if you want to use FUNCTION(...) as a sort of macro function there is a camlp4 filter for that. Let's call close_expr the this macro function (instead of FUNCTION) $ cat expression_closure_filter.ml (* camlp4r *) #default_quotation "expr"; open Camlp4.PreCast; open Format; module FV = Camlp4.Struct.FreeVars.Make Ast; module S = FV.S; value _loc = Loc.ghost; value pervasives = let list = [ "+"; ""; "/"; "*" (* ... *) ] in List.fold_right S.add list S.empty; value collect_free_vars_sets = object (self) inherit FV.fold_free_vars [S.t] S.add ~env_init:pervasives S.empty as super; value free_sets = []; method set_free free = {< free = free >}; method expr = fun [ << close_expr $e$ >> > (self#expr e)#add_current_free#set_free free  e > super#expr e ]; method add_current_free = {< free_sets = [ free :: free_sets ] >}; method free_sets = free_sets; end; value apply_close_expr next_free_set = object (self) inherit Ast.map as super; method expr = fun [ << close_expr $e$ >> > let e = self#expr e in let fv = next_free_set () in S.fold (fun x acc > << fun ~ $x$ > $acc$ >>) fv e  e > super#expr e ]; end; value f st = let fv_sets = ref (collect_free_vars_sets#str_item st)#free_sets in let next_free_set () = match fv_sets.val with [ [] > assert False  [x::xs] > let () = fv_sets.val := xs in x ] in (apply_close_expr next_free_set)#str_item st; AstFilters.register_str_item_filter f; $ ocamlc c pp camlp4rf expression_closure_filter.ml $ cat test_expression_closure_filter.ml (* x and y are free *) close_expr(x y);; (* bind x *) let x = 42;; (* y is free *) close_expr(x y);; (* bind y locally so the expr is closed *) close_expr(let y = x in x y);; (* bind y locally but outside, z is free *) let y = x in close_expr(x z y);; $ camlp4o ./expression_closure_filter.cmo test_expression_closure_filter.ml (* x and y are free *) let _ = fun ~y ~x > x y (* bind x *) let x = 42 (* y is free *) let _ = fun ~y > x y (* bind y locally so the expr is closed *) let _ = let y = x in x y (* bind y locally but outside, z is free *) let _ = let y = x in fun ~z > x z y > Thanks again  the new camlp4 version seem to really shine > w.r.t. the previous one ! Thanks, I'm glad to see camlp4 receive appreciations :) Cheers,  Nicolas Pouillard