Scratching the mutt, part 1: Introducing sendbox

Two years ago I documented my configuration of mutt, offlineimap and courier imap. This combination gave me complete offline access (critical on a laptop) including folders and sending new messages. Additionally it scaled painlessly to multiple servers and clients, without my needing to think about keeping them in sync. Life was good, for a while...

More recently, I decided that I'd like to use mutt with IMAP directly on some client machines (workstations) and offlineimap on other machines (laptops). I rewrote my muttrc to be preprocessed with m4, and everything was rosy, except for sending via Outbox...

The method I was using depended on a helper script (mailout) which called safecat to deposit mail in the Outbox. That script no longer suffices, because it needs to save to IMAP rather than local maildir. Of course we want to use mutt's existing connection to the server rather than create another connection in the script! So I needed to find a way to make it work within mutt.

What started as an elegant hack quickly turned ugly. I tried setting $sendmail=/bin/true and used $record to fcc the message to the IMAP Outbox. This hack generally worked. The fcc-status patch is needed to prevent "Status: RO" (screws up the recipients that use mboxes; the mail shows up as already-read). Additionally mutt doesn't provide a method to fcc to more than one folder, so to get an fcc other than the Outbox, I used the write-fcc function in the compose menu. That was borked though because it lacks the Message-ID, encryption/signing, date, etc!

Moreover it all falls apart when bouncing (remailing) messages, because that code path calls mutt_invoke_sendmail directly, and of course no fcc is done.

Finally I realized that these hackish methods were going nowhere fast, so I implemented Outbox support directly in mutt. I call it "sendbox" because I think that's more explicit. Plus mutt already has an internal variable Outbox that corresponds to the $record setting, and I wanted to avoid confusion.

To use this feature, one does something like:

set sendbox=imaps://imap.domain.com/INBOX/Outbox
set use_sendbox=yes

...then all mail is sent by saving it to the Outbox instead of calling sendmail.

Part 2 in this series will explain this configuration in more detail and provide the patches to make it happen. Later parts will document some other interesting (at least to me) parts of my mutt setup.


JaM part 2: The token tree.

This is part 2 of a series that started here.

First, a quick correction: I claimed that Lisp macros didn't have the ability change the basic syntax of Lisp. I believed that because I hadn't yet learned about "read" macros. Using "read" macros in Lisp you can indeed adjust some pretty basic syntax rules. That can't be done in JaM yet, but it's something that can probably be added in later.

So let's look more closely at the first stages of what JaM does. As stated previously, JaM.include("foo.js") fetches a JavaScript source file as text. It then passes that text to JaM.eval( ... ). The eval function does a lexical analysis of the text (currently using code from JSLint) to generate a JavaScript array of token objects.

A JaM token object is basically just a JSLint token object. For each word read from the JavaScript source, it contains the word itself, the line number and column where it was seen, and other bits of meta-data. Here's a couple of examples:

  value: "function",
  line: 99,
  character: 16,
  reserved: true,
  identifier: true
  value: "'bar'",
  line: 134,
  character: 32,
  type: '(string)'

I'm not sure if all this will be needed or useful in the long run, but JSLint produces it, and I have no good reason to throw any of it away. So far the "value" has been the only part that is has regularly been useful in the macros I've written.

Next, eval uses a few simple grouping rules to generate a tree of nested arrays of token objects. For example, the JavaScript expression "alert('hi!');" would be translated into the following tree:

    { value: "alert", ... },
      { value: "(", ... }
          { value: "'hi!'", ... }
      { value: ")", ... }
    { value: ";", ... }

These grouping rules have to be simple and loose because they must correctly parse not only normal JavaScript but also the code which will be the input to all our macros. (This is the stage where we could be using Lisp-like "read" macros instead of it being hardcoded as it is in JaM currently).

For example, if we plan to define a unless macro, JaM at this stage does not know what the word unless means, but it needs to generate an appropriate tree anyway. So for this expression:

  unless( false ) { alert( 'hi' ); }

JaM generates the tree below. For brevity I'll show just the value of each token object:


This nested tree of token objects is the data structure that JaM macros operate on. What exactly a macro might do with with this structure will be covered in the next installment.


JaM: Lisp-like macros for JavaScript, part 1

A couple weeks ago I was reading Paul Graham's excellent book On Lisp, and I was struck with the thought that many of the features of Lisp he seems to really like are also provided by JavaScript. These include dynamic typing, lexical variable scoping, first-class functions, closures, etc. But macros are of course completely missing from JavaScript.

How hard would it be to add Lisp-like macros to JavaScript, I wondered? I'm learning about Lisp macros for the first time here, so I didn't really know, but I thought it would be fun to try.

This will be the first of several posts describing "JaM", my attempt to add Lisp-like macros to JavaScript.

It seems to me there a few essential ingredients to make a macro system for JavaScript that is as powerful as Lisp's:

  1. Macros are written in JavaScript with access to all functions defined up to that point.
  2. The source code that the macros read and write is in a format that is easy for JavaScript to manipulate, such as a JSON parse tree, not just a big string.

Number 1 is important, because otherwise you end up with something like C or C++ macros -- a weak mini-language that looks and acts differently than the host language. I suppose it's better than nothing, but it doesn't have nearly the language-building power that Lisp macros do.

As for number 2, I suppose it would be possible to set up a system where each macro could match based on a regex or something equally flexible, but this would have a couple of drawback. First, most macros wouldn't need that flexibility and would end up reimplementing the same patterns as other macros, including tricky things like matching up pairs of parens, curly braces, etc. Second, I don't want to try to read code that's being worked over by macros that are that flexible. I'd like to be able to assume that each macro is constrained in its scope, following roughly the same rules as the core JavaScript language. Lisp macros certainly have this restriction, so I'm not worried about this causing my macro system to be too weak.

Let's start off with a function JaM.include("foo.js"), which will fetch the JavaScript file, expand any macros in it, and then run it through the regular JavaScript eval(). Except it's not quite that simple because we want to be able to mix function definitions and macro definitions after each other in any order so they can build on each other. So we'll need to split "foo.js" into top-level expressions that can be correctly evaluated. I'll leave the details of this step for another time, but what's important is that for each top-level expression we will expand any macros and then evaluate it before moving on to the next expression.

This will probably be very slow -- certainly slower than just letting the JavaScript interpreter have at foo.js directly. But if that's the sort of thing that worries you, perhaps you'll be comforted by these thoughts: First, as described here the parsing, macro expansion, and separate evals happen once when a new source file is being loaded. Once the code is up and running there may be no need to do further macro expansion. Second, we could add another step to the processing of each top-level expression: after expanding any macros in an expression we could save the resulting code before evaluating it. Doing this with each expression in turn would result in a file full of fully-expanded normal JavaScript that browsers could run directly and at full speed.

Ok, that was pretty dull; perhaps I can whet your appetite with some sample code? Let's say you really like perl's unless keyword, and you wish JavaScript had something similar. With JaM, you can add it yourself:

defMacro unless( expr, block: body ) {
  return {{
    if( ! ( #expr ) ) {

unless( true == false ) {
  alert( 'Hello, macro-enabled world!' );

It may not be the most useful example one can imagine, and even so I feel I've got a fair bit more to explain before it'll make much sense. We'll build our way up to defMacro, {{ ... }}, and the # operator over the next few posts. Hopefully, though, all of the above will be sufficient for you to understand where I'm headed.

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