sulami / Literate Calc Mode.el

#+TITLE: Literate Calc Mode

[[https://melpa.org/#/literate-calc-mode][file:https://melpa.org/packages/literate-calc-mode-badge.svg]]

Literate programming for =M-x calc=. There is an [[http://sulami.github.io/posts/literate-calc-mode/][announcement blog post]].

Displays inline results for calculations, supports variables and updates as you type (if you want). Also works in your favourite markup mode.

#+caption: Demo [[file:./scrot.png]]

• Installing

Simply grab it from [[https://melpa.org/][MELPA]].

** [[https://github.com/jwiegley/use-package][use-package]]

#+begin_src emacs-lisp (use-package literate-calc-mode :ensure t) #+end_src

** [[https://github.com/raxod502/straight.el][straight.el]]

#+begin_src emacs-lisp (straight-use-package 'literate-calc-mode) #+end_src

** package.el

[[https://melpa.org/#/getting-started][Ensure you have MELPA available.]]

=M-x package-install=, select =literate-calc-mode=.

** Manual

Just fetch [[file:literate-calc-mode.el][literate-calc-mode.el]], save it somewhere and load it into Emacs.

• Configuration

There is a =M-x customize= group named after the mode which contains the following options:

| literate-calc-mode-idle-time | How long to wait after typing to recalculate results | | literate-calc-mode-inhibit-line-functions | Hook functions called for each line to test whether to inhibit calculation |

The idle time prevents lag due to constant recalculation in the middle of typing, defaulting to 1 second.

There is currently a single inhibitor, which comes installed by default:

• literate-calc-mode-inhibit-in-src-blocks :: Prevents evaluation inside org-mode src blocks

Of course you can also just setq the options directly.

• Use

There is both a major literate-calc-mode and a minor literate-calc-minor-mode. The major mode does some basic syntax highlighting, while the minor mode only evaluates all calc statements while typing.

The minor mode works quite well with org-/markdown mode or other markup language major modes.

There are also some functions which can be called without any mode being active:

| =M-x literate-calc-eval-line= | Evaluates a single line | | =M-x literate-calc-eval-buffer= | Evaluates the whole buffer | | =M-x literate-calc-insert-results= | Evaluates the whole buffer and inserts results | | =M-x literate-calc-clear-overlays= | Removes all overlays and clears variables | | =M-x literate-calc-remove-results= | Removes all results and clears variables |

** Using Units

You can simply append units to your values like so:

#+begin_src fundamental Flour = 500g => Flour: 500 g #+end_src

Unit conversion (and other complex functions) can be used by invoking the matching [[https://www.gnu.org/software/emacs/manual/html_node/calc/Function-Index.html][Algebraic Function]].

#+begin_src fundamental = usimplify(1m + 3mm) => 1.003 m #+end_src

You can also use unknown mathematical symbols:

#+begin_src fundamental = x*2 + x-3 => 3 x - 3 #+end_src

** Evaluation in Org

Org-mode source blocks can be evaluated (C-c C-c by default).

If :results is set to value, which is the default, a block returns its last result. If :results is set to output, it will return the entire block, annotated with results.

Local variables can be defined in header arguments as :var a=38 b=4.

• Full Example

#+begin_src fundamental This is a literate calc file.

Lines without "=" are ignored.

All results starting with "=>" are an overlay generated by literate-calc-mode. That means they are displayed in Emacs, but not actually in the buffer/file contents.

We can calculate a value like so:

= 2 + 2 => 4

If there is any string on the left hand side, it becomes a bound variable.

Pi = 3.14159 => Pi: 3.14159

We can use this variable below the definiton.

Tau = Pi * 2 => Tau: 6.28318

Results are calculated using Emacs' own calc, so you can use formulas as well.

= round(Pi, 2) => 3.14

Later bindings shadow earlier ones:

Pi = 3 => Pi: 3

= Pi => 3

Variable names can have spaces as well:

Monthly Expenses = 500 => Monthly Expenses: 500

Monthly Income = 1000 => Monthly Income: 1000

Annual Savings = 12 * (Monthly Income - Monthly Expenses) => Annual Savings: 6000

All values are recalculated on every update in a spreadsheet-like fashion.

Calc also has a lot of advanced features, like arrays:

Numbers = [1 2 3] => Numbers: [1, 2, 3]

= 3 Numbers => [3, 6, 9]

#+end_src

• Roadmap

There are some additional features I'm currently thinking about.

** Semantic Highlighting

One of the original inspirations was [[http://tydligapp.com/][Tydlig]], which does similar things, but also has semantic highlighting. That means, variables are highlighted in different colours, but always the same one for a given variable, so that you can see where it's used at a glance.

I might steal some code from [[https://github.com/Fanael/rainbow-identifiers][rainbow-identifiers]], which is one of the [[https://github.com/ankurdave/color-identifiers-mode][shorter existing implementations]] around, and adapt that to our needs.