From: Jacques Garrigue <garrigue@math.nagoya-u.ac.jp>
To: jonathan.roewen@gmail.com
Cc: caml-list@yquem.inria.fr
Subject: Re: [Caml-list] HOFs, recursion, and being tail-rec...
Date: Mon, 13 Feb 2006 08:53:48 +0900 (JST) [thread overview]
Message-ID: <20060213.085348.126575598.garrigue@math.nagoya-u.ac.jp> (raw)
In-Reply-To: <ad8cfe7e0602121408q15124406ta0e3a42a69c0abcc@mail.gmail.com>
From: Jonathan Roewen <jonathan.roewen@gmail.com>
>
> I have a simple implementation of depth-first-search, and was
> wondering if my approach would qualify as tail-rec (whether from the
> code it is/isn't, and whether ocaml can optimise it so it is).
By definition a depth-first-search cannot be tail-recursive: you need
a stack to implement the backtracking.
There is a degenerate case where all nodes are non-branching
(i.e. there is only one path), which in theory could be made
tail-recursive. But it would not be the case with your code, as
List.exists has no special case for the last element of the list (not
that it would make a lot of sense in general.)
> val positions : 'a -> ('a * 'a) list -> 'a list -> 'a list
> (* I think that's right type: returns positions we can traverse to,
> omitting nodes we've previously visited *)
>
> (* val dfs: 'a -> 'a -> ('a * 'a) list -> bool *)
> let dfs start goal edges =
> let rec search visited position =
> if position = goal then true
> else List.exists (search (position::visited)) (positions
> position edges (position::visited))
> in search [] start;;
next prev parent reply other threads:[~2006-02-12 23:52 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-02-12 22:08 Jonathan Roewen
2006-02-12 23:53 ` Jacques Garrigue [this message]
2006-02-13 2:05 ` skaller
2006-02-13 2:47 ` Jonathan Roewen
2006-02-13 3:23 ` skaller
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