From: Dario Teixeira <darioteixeira@yahoo.com>
To: caml-list@yquem.inria.fr
Subject: Sources, sinks, and unbound parameter types
Date: Mon, 24 Mar 2008 21:56:09 +0000 (GMT) [thread overview]
Message-ID: <535050.42465.qm@web54603.mail.re2.yahoo.com> (raw)
Hi,
I'm looking for a way to express the composition of functional components
in a tree-like data structure. Each node in the tree is either:
a) a Source, producing values "out of nowhere": unit -> 'a
b) a Sink, end point of the tree: 'b -> unit
c) a Processor, transforming values from one type to another: 'c -> 'd
The Ocaml type that represents a node is as follows: (pretty
straightforward, though I wonder if there's a way to explicitly
say that "Source is of 'a -> 'b where 'a must be of type unit")
type ('a, 'b) node_t =
| Source of (unit -> 'b)
| Sink of ('a -> unit)
| Processor of ('a -> 'b)
In addition, there are two types of connectors linking these nodes in the tree:
a) a Pipe, connecting one node that outputs a value of type 'a into
another that inputs an 'a.
b) a Splitter, essentially like a Pipe, but able to feed the same
value into multiple inputs.
If you'll pardon the ASCII art, here's a diagram of one such simple tree:
| ===========
| | source1 |
| ===========
| |
| |
| O Pipe
| |
| |
| ============
| | process1 |
| ============
| |
| |
| ----------------O----------------
| | Splitter |
| | |
| =========== ===========
| | sink1 | | sink2 |
| =========== ===========
Where each component node can, for example, be defined as follows:
let source1 () = 10
let process1 n = 2.0 *. (float_of_int n)
let sink1 x = Printf.printf "Sink1: %f\n" x
let sink2 x = Printf.printf "Sink2: %f\n" x
To define the tree type, I would like to express something like the code
below. Note that I am trying to get to the compiler to statically enforce
that outputs and inputs are correctly matched type-wise.
type ('a, 'b) tree_t =
| Node of ('a, 'b) node_t
| Pipe of ('a, 'c) tree_t * ('c, 'b) tree_t
| Splitter of ('a, 'c) tree_t * ('c, 'b) tree_t list
The code above obviously won't work because of the unbound type parameter 'c.
(Also, please ignore for now the fact it allows splitters with an empty
output list -- that can easily be circumvented).
So, my question is if there is any way to express what I want? I guess there
is a solution involving the creation of a syntax extension, but I'm looking
for a pure Ocaml way.
Thanks in advance for your time!
Best regards,
Dario Teixeira
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next reply other threads:[~2008-03-24 21:56 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-03-24 21:56 Dario Teixeira [this message]
2008-03-24 22:17 ` [Caml-list] " Daniel Bünzli
2008-03-24 22:19 ` Christopher L Conway
2008-03-24 23:03 ` Jeremy Yallop
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