SML mode is a major mode for Emacs for editing Standard ML. It has some novel bugs, and some nice features:
| automatically determines if it is used
in a case or fun construct, and indents the next line as appropriate,
inserting => or the name of the function.
Contributions to the package are welcome. I have limited time to work on this project, but I will gladly add any code that you contribute to me to this package.
Although the history of sml-mode is obscure, it seems that the following persons have made contributions to sml-mode:
You’re reading it. Apart from the on-line info tree (C-h i is the
Emacs key to enter the info system—you should follow the brief
tutorial if this is unfamiliar), there are further details on specific
commands in their documentation strings. Only the most useful
SML mode commands are documented in the info tree: to find out more,
use Emacs’ help facilities.
Briefly, to get help on a specific function use C-h f and enter
the command name. All (almost all, then) SML mode commands begin
with sml-, so if you type this and press TAB (for
completion) you will get a list of all commands. Another way is to use
C-h a and enter the string sml. This is command apropos; it
will list all commands with that sub-string in their names, and any key
binding they may have in the current buffer. Command apropos gives a
one-line synopsis of what each command does.
Some commands are also variables—such things are allowed in Lisp, if not in ML! See Command Index, for a list of (info) documented functions. See Variable Index, for a list of user settable variables to control the behaviour of SML mode.
Before accessing this information on-line from within Emacs you may have
to set the variable sml-mode-info. Put in your .emacs file
something like:
(setq sml-mode-info "/home/mjm/info/sml-mode.info")
When different from the default this variable should be a string giving the absolute name of the .info file. Then C-c C-i in SML mode (i.e., the command M-x sml-mode-info) will bring up the manual. This help is also accessible from the menu. (Resetting this variable will not be necessary if your site administrator has been kind enough to install SML mode and its attendant documentation in the Emacs hierarchy.)
Now SML mode provides just a few additional editing commands. Most of the work has gone into implementing the indentation algorithm which, if you think about it, has to be complicated for a language like ML. See Indentation Defaults, for details on how to control some of the behaviour of the indentation algorithm. Principal goodies are the ‘electric pipe’ feature, and the ability to insert common SML forms (macros or templates).
This switches a buffer into SML mode. This is a major mode in
Emacs. To get out of SML mode the buffer’s major mode must be set to
something else, like text-mode.
Emacs is all hooks of course. A hook is a variable: if the variable is non-nil it binds a list of Emacs Lisp functions to be run in some order (usually left to right). You can customise SML mode with these hooks:
Default: nil
This is run every time a new SML mode buffer is created (or if you type M-x sml-mode). This is one place to put your preferred key bindings. See Configuration Summary, for some examples.
ML is a complicated language to parse, let alone compile. The indentation algorithm is a little wooden (for some tastes), and the best advice is not to fight it! There are several variables that can be adjusted to control the indentation algorithm (see Customising SML Mode, below).
This command indents the current line. If you set the indentation of the
previous line by hand, indent-for-tab-command will indent relative to
this setting.
Indent the current region. Be patient if the region is large (like the whole buffer).
Unindents the line to the next outer level of indentation.
Further indentation commands that Emacs provides (generically, for all modes) that you may like to recall:
On LFD by default. Insert a newline, then indent according to the major mode. See Indentation for Programs in The Emacs Editor Manual, for details.
On C-x TAB by default. Moves all lines in the region right by its argument (left, for negative arguments). See Indentation in The Emacs Editor Manual.
On M-; by default. Indent this line’s comment to comment column, or insert an empty comment. See Comment Commands in The Emacs Editor Manual.
On M-LFD by default. Break line at point and indent, continuing comment if within one. See Multi-Line Comments in The Emacs Editor Manual.
As with other language modes, M-; gives you a comment at the end
of the current line. The column where the comment starts is determined
by the variable comment-column—default is 40, but it can be
changed with set-comment-column (on C-x ; by default).
Electric keys are generally pretty irritating, so those provided by SML mode are fairly muted. The only truly electric key is ;, and this has to be enabled to take effect.
When the point is in a ‘case’ statement this opens a new line, indents
and inserts | => leaving point just before the double arrow; if
the enclosing construct is a ‘fun’ declaration, the newline is indented
and the function name copied at the appropriate column. Generally, try
it whenever a | is wanted—you’ll like it!
When the point is after a keyword like ‘let’, this inserts the
corresponding predefined skeleton if one exists. Else it just inserts a
space. Another way to insert those skeletons is to use
sml-insert-form, described below.
Interactive short-cut to insert common ML forms (a.k.a. macros, or templates). Recognised forms are ‘let’, ‘local’, ‘case’, ‘abstype’, ‘datatype’, ‘signature’, ‘structure’, and ‘functor’. Except for ‘let’ and ‘local’, these will prompt for appropriate parameters like functor name and signature, etc.. This command prompts in the mini-buffer, with completion.
By default C-c RET will insert at point, with the indentation of the current column; if you give a prefix argument (i.e., C-u C-c RET) the command will insert a newline first, indent, and then insert the template.
sml-insert-form is also extensible: see Configuration Summary for
further details.
Several variables try to control the indentation algorithm and other features of SML mode. Most of them are still in flux so they are not described here yet. If the default values are not acceptable you can set these variables permanently in your .emacs file. See Configuration Summary, for details and examples.
Default: 4
This variable controls the block indentation level.
The most useful feature of SML mode is that it provides a convenient interface to the compiler. How serious users of ML put up with a teletype interface to the compiler is beyond me... but perhaps there are other interfaces to compilers that require one to part with serious money. Such remarks can quickly become dated—in this case, let’s hope so!
Anyway, SML mode provides an interaction mode,
inferior-sml-mode, where the compiler runs in a separate buffer
in a window or frame of its own. You can use this buffer just like a
terminal, but it’s usually more convenient to mark some text in the
SML mode buffer and have Emacs communicate with the sub-process. The
features discussed below are syntax-independent, so they should work
with a wide range of ML-like tools and compilers. See Process defaults, for some hints.
inferior-sml-mode is a specialisation of the comint
package that comes with Emacs and XEmacs.
Start your favourite ML compiler with the command
M-x run-sml
This creates a process interaction buffer that inherits some key bindings from SML mode and from comint (see Shell Mode in The Emacs Editor Manual). Starting the ML compiler adds some functions to SML mode buffers so that program text can be communicated between editor and compiler (see Speaking to the compiler).
The name of the ML compiler is the first thing you should know how to specify:
Default: "sml"
The program to run as ML. You might need to specify the full path name of the program.
Default: ""
Useful for Poly/ML users who may supply a database file, or others who
have wrappers for setting various options around the command to run the
compiler. Moscow ML people might set this to "-P full", etc..
The variable sml-program-name is a string holding the name
of the program as you would type it at the shell. You
can always choose a program different to the default by invoking
C-u M-x run-sml
With the prefix argument Emacs will prompt for the command name and any command line arguments to pass to the compiler. Thereafter Emacs will use this new name as the default, but for a permanent change you should set this in your .emacs with, e.g.:
(setq sml-program-name "nj-sml")
Launches ML as an inferior process in another buffer; if an ML process already exists, just switch to the process buffer. A prefix argument allows you to edit the command line to specify the program, and any command line options.
Default: nil
M-x run-sml runs comint-mode-hook and
inferior-sml-mode-hook hooks in that order, but after the
compiler is started. Use inferior-sml-mode-hook to set any
comint buffer-local configurations for SML mode you like.
Switch from the SML buffer to the interaction buffer. By default point will be placed at the end of the process buffer, but a prefix argument will leave point wherever it was before. If you try C-c C-s before an ML process has been started, you’ll just get an error message to the effect that there’s no current process buffer.
When started, the ML compiler’s default working directory is the
current buffer’s default directory. This command allows the working
directory to be changed, if the compiler can do this. The variable
sml-cd-command specifies the compiler command to invoke
(see Process defaults).
Several commands are defined for sending program fragments to the running compiler. Each of the following commands takes a prefix argument that will switch the input focus to the process buffer afterwards (leaving point at the end of the buffer):
Send a ‘use file’ command to the current ML process. The variable
sml-use-command is used to define the correct template for the
command to invoke (see Process defaults). The default file is the
file associated with the current buffer, or the last file loaded if you
are in the interaction buffer.
Send the current region of text in the SML buffer.
sml-send-region-and-go is a similar command for you to bind in
SML mode if you wish: it’ll send the region and then switch-to-sml.
Send the contents of the current buffer to ML.
SML mode provides one customisable function for locating the source
position of errors reported by the compiler. This should work whether
you type use "puzzle.sml"; into the interaction buffer, or use
one of the mechanisms provided for sending programs directly to the
compiler—see Speaking to the compiler.
Jump to the source location of the next error reported by the compiler. All the usual error-navigation commands are available, see see Compilation Mode in The Emacs Editor Manual.
The process interaction code is independent of the compiler used, deliberately, so SML mode will work with a variety of ML compilers and ML-based tools. There are therefore a number of variables that may need to be set correctly before SML mode can speak to the compiler. Things are by default set up for Standard ML of New Jersey, but switching to a new system is quite easy.
Default: "use \"%s\""
Use file command template. Emacs will replace the %s with a file
name. Note that Emacs requires double quote characters inside strings
to be quoted with a backslash.
Default: "OS.FileSys.chDir \"%s\""
Compiler command to change the working directory. Not all ML systems support this feature (well, Edinburgh (core) ML didn’t), but they should.
Default: "^[-=>#] *"
Matches the ML compiler’s prompt: comint uses this for various purposes.
To customise error reportage for different ML compilers you need to set
two further variables before next-error can be useful:
Alist that specifies how to match errors in compiler output. Each elt has the form (REGEXP FILE-IDX LINE-IDX [COLUMN-IDX FILE-FORMAT...]) If REGEXP matches, the FILE-IDX’th subexpression gives the file name, and the LINE-IDX’th subexpression gives the line number. If COLUMN-IDX is given, the COLUMN-IDX’th subexpression gives the column number on that line. If any FILE-FORMAT is given, each is a format string to produce a file name to try; %s in the string is replaced by the text matching the FILE-IDX’th subexpression.
This (sort of pedagogic) section gives more information on how to configure SML mode: menus, key bindings, hooks and highlighting are discussed, along with a few other random topics.
One way to set SML mode variables (see Indentation Defaults), and other defaults, is through the
sml-mode-hook in your .emacs. A simple example:
(defun my-sml-mode-hook () "Local defaults for SML mode" (setq sml-indent-level 2) ; conserve on horizontal space (setq words-include-escape t) ; \ loses word break status (setq indent-tabs-mode nil)) ; never ever indent with tabs (add-hook 'sml-mode-hook #'my-sml-mode-hook)
The body of my-sml-mode-hook is a sequence of assignments. In this
case it is not really necessary to set sml-indent-level in a hook
because this variable is global (most SML mode variables are). With
similar effect:
(setq sml-indent-level 2)
anywhere in your .emacs file. The variable indent-tabs-mode is
automatically made local to the current buffer whenever it is set
explicitly, so it must be set in a hook if you always want
SML mode to behave like this.
Another hook is inferior-sml-mode-hook. This can be used to
control the behaviour of the interaction buffer through various
variables meaningful to comint-based packages:
(defun my-inf-sml-mode-hook () "Local defaults for inferior SML mode" (add-hook 'comint-output-filter-functions 'comint-truncate-buffer) (setq comint-scroll-show-maximum-output t) (setq comint-input-autoexpand nil)) (add-hook 'inferior-sml-mode-hook 'my-inf-sml-mode-hook)
Again, the body is a sequence of assignments. Unless you run several ML
compilers simultaneously under one Emacs, this hook will normally only
get run once. You might want to look up the documentation (C-h v
and C-h f) for these buffer-local comint things.
Customisation (in Emacs) usually entails putting favourite commands on
easily remembered keys. Two ‘keymaps’ are defined in SML mode: one
is effective in program text buffers (sml-mode-map) and the other
is effective in interaction buffers (inferior-sml-mode-map).
The initial design ensures that (many of) the default key bindings from
the former keymap will also be available in the latter (e.g.,
C-c`).
Type C-h m in an SML mode buffer to find the default key bindings (and similarly in an ML interaction buffer), and use the hooks provided to install your preferred key bindings. Given that the keymaps are global (variables):
(defun my-sml-mode-hook () "Global defaults for SML mode" (define-key sml-mode-map "\C-cd" 'sml-cd)) (add-hook 'sml-mode-hook 'my-sml-mode-hook)
This has the effect of binding sml-cd to the key C-c d.
If you want the same behaviour from C-c d in the ML buffer:
(defun my-inf-sml-mode-hook () "Global defaults for inferior SML mode" (define-key inferior-sml-mode-map "\C-cd" 'sml-cd) ;; NB. for SML/NJ '96 (setq sml-cd-command "OS.FileSys.chDir \"%s\"")) (add-hook 'inferior-sml-mode-hook 'my-inf-sml-mode-hook)
There is nothing to stop you rebuilding the entire keymap for
SML mode and the ML interaction buffer in your .emacs of
course: SML mode won’t define sml-mode-map or
inferior-sml-mode-map if you have already done so.
Highlighting is very handy for picking out keywords in the program text, spotting misspelled kewyords, and, if you have Emacs’ ps-print package installed (you usually do these days), obtaining pretty, even colourful code listings—quite properly for your colourful ML programs.
The indentation scheme (strangely enough) also relies on the highlighting code to properly handle nested comments, which is yet another reason to turn on highlighting. To turn on highlighting, use either of:
M-x font-lock-mode (add-hook 'sml-mode-hook 'turn-on-font-lock) (global-font-lock-mode 1)
The first will turn it on in the current buffer. The second will turn it on in all sml-mode buffers. The last will turn it on everywhere. This is valid for Emacs but maybe not for XEmacs. Check font-lock documentation if you encounter problems.
These forms are bloody useless; can’t we have better ones?
You can indeed. sml-insert-form is extensible so all you need to
do is create the macros yourself. Define a keyboard macro
(C-x ( <something> C-x )) and give it a suitable name:
sml-addto-forms-alist prompts for a name, say NAME, and
binds the macro sml-form-NAME. Thereafter C-c RET
NAME will insert the macro at point, and C-u C-c RET NAME
will insert the macro after a newline-and-indent. If you want to
keep your macros from one editing session to the next, go to your
.emacs file and call insert-kbd-macro; you’ll need
to add NAME to sml-forms-alist permanently yourself:
(defun my-sml-mode-hook () "Global defaults for SML mode"
;; whatever else you do
(add-to-list 'sml-forms-alist '("NAME" . FUNCTION)))
If you want to create templates like ‘case’ that prompt for parameters
you’ll have to do some Lisp programming. The skeleton package is
a good stating point. Better yet, you can reuse the wrappers used by
sml-mode itself in your sml-mode-hook:
(add-hook 'sml-mode-hook
(lambda ()
(sml-def-skeleton "case" "Case expr: "
str " of" \n _ " => ")))
This will redefine ‘case’ in order to leave the ‘of’ on the first line.
See the documentation of skeleton-insert to get a better
understanding of how this works.
I hate that indentation algorithm; can’t I tweak it?
Ah, yes, of course, but this manual will not tell you how.
Can SML mode handle more than one compiler running at once?
Sure, just rename the ‘*sml*’ buffer and then use run-sml
as usual.
What needs to be done to support other ML compilers?
Not much really. Just add the right regular expressions to
sml-error-regexp-alist and that should be all.
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