/*
 * title Calculating
 * author "Dylan Lom"
 * date 2021-04-23
 * link stylesheet /main.css
 */

# $(echo "$title")

I've been trying to solidify a concept for a RPN-style calculator in my head for
a while now, I figured it might be good to try and actually write down some
example uses to cement it.

The main *feature* I wanted to add was some FP-esque list operations (ie. map,
fold) that would operate on your existing stack; just because I have in the past
thought "wow it'd be nice if I didn't need to mash the '+' key to add all these
numbers".

## Basics

It'd be the same as any RPN calculator for the basics.

    1           ; stack = 1
    2 3 +       ; stack = 1, 5
    +           ; stack = 6
    10 -        ; stack = -4

## Variables

It'd probably be nice to have variables too? I'm not sure about how I'd do the
syntax here.

    1 2 3        ; stack = 1, 2, 3  |
    => a         ; stack = 1, 2     | a = 3
    a            ; stack = 1, 2, 3  | a = 3

## List operations

Again, the syntax is totally up in the air.

For this example I've arbitrarily picked `:=` for map, `<<` for foldr and `>>`
for foldl.

    1 2 3        ; stack = 1, 2, 3
    := (1 +)     ; stack = 2, 3, 4
    << *         ; stack = (4 * 3 * 2) = 24
    1 + 5 2      ; stack = 25, 5, 2
    >> /         ; stack = (25 / 5 / 2) = 2.5

## Does this already exist?

Probably -- if not the answer would be 'just use language *x*'s REPL' -- but it
seems like it could be a fun weekend-y project.

I'd kind-of like to learn some Lisp or Scheme anyway and they seem like good
languages to do this sort of thing in?

Alternatively `dc` seems like it might already be able to do this -- or at least
a reasonable place to fork from.