* Problem with local modules
@ 2005-04-18 14:02 Alex Baretta
0 siblings, 0 replies; only message in thread
From: Alex Baretta @ 2005-04-18 14:02 UTC (permalink / raw)
To: Ocaml
I have written a list-of-sorted-lists merging function which takes
advantage of a functional heap module by Jean-Christophe Filliatre. I
would like to avoid the functorial style of the heap library by using
local modules; however, the type system does not allow me to bind the
"type t" of the local parameter module to a type variable, which is
bound in the containing expression.
This is what I would like to have:
let rev_merge_list_rev_filter_append
(cmp : 'a -> 'a -> int)
(p : 'a -> bool)
(ll : 'a list list)
(accu : 'a list)
=
let module Ordered = struct
type t = Obj.t * (Obj.t list)
let compare (x,tlx) (y,tly) = cmp ((Obj.obj x):'a) ((Obj.obj y):'a)
end in
let module Heap = Heap.Functional (Ordered)
in
...
This is what I had to write.
let rev_merge_list_rev_filter_append
(cmp : 'a -> 'a -> int)
(p : 'a -> bool)
(ll : 'a list list)
(accu : 'a list)
=
let module Ordered = struct
type t = Obj.t * (Obj.t list)
let compare (x,tlx) (y,tly) = cmp ((Obj.obj x):'a) ((Obj.obj y):'a)
end in
let module Heap = Heap.Functional (Ordered)
in
...
Is this a limitation of the type theory or of the type checker? Is there
any other way out than using the Obj module?
Alex
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