From: "Josh Berdine" <email@example.com> To: "Richard W.M. Jones" <firstname.lastname@example.org> Subject: Re: [Caml-list] Syntax puzzle / suggestion Date: Fri, 09 Aug 2019 15:51:39 +0100 Message-ID: <BD3A01EE-3256-4C45-A217-FF2B6D659FBA@berdine.net> (raw) In-Reply-To: <email@example.com> What about good old-fashioned state: let all_items = ref  let add_item item = all_items := (item :: !all_items, item) let item1 = add_item "hello" let item2 = add_item "world" let all_items = List.rev !all_items On 9 Aug 2019, at 15:27, Richard W.M. Jones wrote: > Let's imagine you have a list of named things, but you also want to > collect them up into a single list. For example: > > let item1 = "hello" > let item2 = "world" > let all_items = [ item1; item2 ] > > let () = > printf "item1 = %s\n" item1; > printf "all_items = %s\n" (String.concat ", " all_items) > > This is fine, but there's a danger that a programmer could add item3 > but forget to add it to the "all_items" list. (In the real world > problem to which this applies, my items are complex and lengthy > structures, and the "all-things-list" is well off the bottom of the > page when you're viewing the top item). > > My idea to fix this was to write: > > let all_items = [ > ("hello" as item1); > ("world" as item2); > ] > > Actually I was slightly surprised to find this doesn't compile. I > guess because "as" can only be used like this in patterns, not > expressions. Also the scoping is wrong because the "as item1" if it > worked probably wouldn't apply outside the list. > > I haven't worked out if it's possible to write this in ordinary OCaml, > although I suppose ppx could solve it. Any ideas if this is possible? > > Rich.
next prev parent reply index Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-08-09 14:27 Richard W.M. Jones 2019-08-09 14:40 ` Gabriel Scherer 2019-08-09 14:45 ` Richard W.M. Jones 2019-08-09 14:48 ` Martin Riener 2019-08-10 5:19 ` rixed 2019-08-09 14:51 ` Josh Berdine [this message] 2019-08-10 15:18 ` Oliver Bandel 2019-08-10 20:34 ` Chet Murthy 2019-08-09 14:56 ` Frédéric Bour
Reply instructions: You may reply publically to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=BD3A01EE-3256-4C45-A217-FF2B6D659FBA@berdine.net \ --firstname.lastname@example.org \ --email@example.com \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: link
caml-list - the Caml user's mailing list Archives are clonable: git clone --mirror http://inbox.vuxu.org/caml-list git clone --mirror https://inbox.ocaml.org/caml-list Newsgroup available over NNTP: nntp://inbox.vuxu.org/vuxu.archive.caml-list AGPL code for this site: git clone https://public-inbox.org/ public-inbox