Extending nand2tetris.el

Great News! nand2tetris.el is now on MELPA.

So, following last blog post about developing a major mode for nand2tetris (which by the way is following the recommendations here, I went on adding a company, eldoc(WIP), and yasnippet backend.

First things first: I did a horrible mistake in last blog post by suggesting indirectly that it's fine to have top-level symbols like HardwareSimulator which was pointed out by @purcell (sry m8) in the MELPA PR.

Now, off to the Implementation of features

Company Backend

I used the HDL Survival Guide from the course resources to have all the possible builtin chips and tried to have a little alist that holds the name of the chip and it's spec. (My next goal is to have a Doc Buffer with more info about the Chip).

;;; Company
(require 'company)
(require 'cl-lib)

(defvar nand2tetris-builtin-chips
  '(("Add16" . (("spec" . "Add16(a= ,b= ,out= )")))
    ("ALU" . (("spec" . "ALU(x= ,y= ,zx= ,nx= ,zy= ,ny= ,f= ,no= ,out= ,zr= ,ng= )")))
    ("And16" .  (("spec" . "And16(a= ,b= ,out= )")))
    ("And" . (("spec" . "And(a= ,b= ,out= )")))
    ("ARegister" . (("spec" . "ARegister(in= ,load= ,out= )")))
    ("Bit" . (("spec" . "Bit(in= ,load= ,out= )")))
    ("CPU" . (("spec" . "CPU(inM= ,instruction= ,reset= ,outM= ,writeM= ,addressM= ,pc= )")))
    ("DFF" . (("spec" . "DFF(in= ,out= )")))
    ("DMux4Way" . (("spec" . "DMux4Way(in= ,sel= ,a= ,b= ,c= ,d= )")))
    ("DMux8Way" . (("spec" . "DMux8Way(in= ,sel= ,a= ,b= ,c= ,d= ,e= ,f= ,g= ,h= )")))
    ("DMux" . (("spec" . "DMux(in= ,sel= ,a= ,b= )")))
    ("DRegister" . (("spec" . "DRegister(in= ,load= ,out= )")))
    ("FullAdder" . (("spec" . "FullAdder(a= ,b= ,c= ,sum= ,carry= )")))
    ("HalfAdder" . (("spec" . "HalfAdder(a= ,b= ,sum= , carry= )")))
    ("Inc16" . (("spec" . "Inc16(in= ,out= )")))
    ("Keyboard" . (("spec" . "Keyboard(out= )")))
    ("Memory" . (("spec" . "Memory(in= ,load= ,address= ,out= )")))
    ("Mux16" . (("spec" . "Mux16(a= ,b= ,sel= ,out= )")))
    ("Mux4Way16" . (("spec" . "Mux4Way16(a= ,b= ,c= ,d= ,sel= ,out= )")))
    ("Mux8Way16" . (("spec" . "Mux8Way16(a= ,b= ,c= ,d= ,e= ,f= ,g= ,h= ,sel= ,out= )")))
    ("Mux" . (("spec" . "Mux(a= ,b= ,sel= ,out= )")))
    ("Nand" . (("spec" . "Nand(a= ,b= ,out= )")))
    ("Not16" . (("spec" . "Not16(in= ,out= )")))
    ("Not" . (("spec" . "Not(in= ,out= )")))
    ("Or16" . (("spec" . "Or16(a= ,b= ,out= )")))
    ("Or8Way" . (("spec" . "Or8Way(in= ,out= )")))
    ("Or" . (("spec" . "Or(a= ,b= ,out= )")))
    ("PC" . (("spec" . "PC(in= ,load= ,inc= ,reset= ,out= )")))
    ("RAM16K" . (("spec" . "RAM16K(in= ,load= ,address= ,out= )")))
    ("RAM4K" . (("spec" . "RAM4K(in= ,load= ,address= ,out= )")))
    ("RAM512" . (("spec" . "RAM512(in= ,load= ,address= ,out= )")))
    ("RAM64" . (("spec" . "RAM64(in= ,load= ,address= ,out= )")))
    ("RAM8" . (("spec" . "RAM8(in= ,load= ,address= ,out= )")))
    ("Register" . (("spec" . "Register(in= ,load= ,out= )")))
    ("ROM32K" . (("spec" . "ROM32K(address= ,out= )")))
    ("Screen" . (("spec" . "Screen(in= ,load= ,address= ,out= )")))
    ("Xor" . (("spec" . "Xor(a= ,b= ,out= )"))))
  "Built In Chips Alist")

(defun company-nand2tetris--candidates (prefix)
  (let ((res))
    (dolist (option nand2tetris-builtin-chips)
      (let ((name (car option)))
        (when (string-prefix-p prefix name)
          (push name res))))

(defun company-nand2tetris--annotation (candidate)
  (message candidate)
  (let ((spec (cdr (assoc "spec" (assoc candidate nand2tetris-builtin-chips)))))
    (format "\t%s" spec)))

(defun company-nand2tetris--grab-symbol ()
      (buffer-substring (point) (save-excursion (skip-syntax-backward "w_.")

(defun company-nand2tetris--prefix ()
  "Grab prefix at point."
  (or (company-nand2tetris--grab-symbol)

(defun company-nand2tetris (command &optional arg &rest ignored)
  (interactive (list 'interactive))
  (cl-case command
    (interactive (company-begin-backend 'company-nand2tetris))
    (prefix (company-nand2tetris--prefix))
    (candidates (company-nand2tetris--candidates arg))
    (annotation (company-nand2tetris--annotation arg))))

Then you'd just have to add this company-nand2tetris backend to company-backeds and you are good to go! :). Here we also define a company-nand2tetris--grab-symbol function that will come handy when creating the ElDoc integration (actually, it goes half way as it only gets the part of the symbol before the current position, any help is appreciated). I followed company-backend creation from their -official?- wiki.


ElDoc support is pretty straight forward, although I still don't get some stuff. In few words, each time your cursor is iddle, the value of the variable eldoc-documentation-function is called, and what is printed is printed in the minibuffer.

What we do for nand2tetris is that each time you rest on the end of a Chip Name it tries to give you the specificatino for such chip, kinda like the annotations from company-nand2tetris, but this time you can access them at any time without the popup showing.

;;; ElDoc
(require 'eldoc)
(defun nand2tetris-eldoc-function ()
  "Get help on SYMBOL using `help'.
Interactively, prompt for symbol."
  (let ((symbol (company-nand2tetris--grab-symbol))
        (enable-recursive-minibuffers t))
  (message (cdr (assoc "spec" (assoc symbol nand2tetris-builtin-chips))))))

(define-derived-mode nand2tetris-mode prog-mode
  "Major mode for editing HDL files for the course Nand2Tetris.


  (set (make-local-variable 'eldoc-documentation-function)

  ;; Fix Comment Syntax
  (set (make-local-variable 'comment-start) "// ")
  (set (make-local-variable 'comment-start-skip) "//+\\s-*")

  (set (make-local-variable 'font-lock-defaults)
       '(nand2tetris-font-lock-keywords nil nil nil nil)))


Finally YASnippet integration is one of the features I always wanted for this mode, ever since the first time I opened the hdl files, unfortunately, snippets for this are pretty straight forward, just create functions to add the snippet dir when yasnippet gets loaded. As we don't want to bother the user with a dependency we use eval-after-load so if the user doesn't use yasnippets it's not a problem.... I ... guess?

;;; Yasnippet

(defconst nand2tetris::dir (file-name-directory (or load-file-name
(defun nand2tetris//snippets-initialize ()
  (let ((snip-dir (expand-file-name "snippets" nand2tetris::dir)))
    (add-to-list 'yas-snippet-dirs snip-dir t)
    (yas-load-directory snip-dir)))

(eval-after-load 'yasnippet

You can see how snippets are supposed to look like in the repo.


That was all I did today and I'm sharing it with ya :) I hope this might eventually be featured in the nand2tetris official course :) because it would be awesome, so if someone can make this happen, plz do.