rio🦜

A little language, that I'm developing to practice crafting interpreters.

Why?

For some reason, programming language designers are still making such things as arithmetical operations, pipe operators (. in haskell, |> in f-sharp) and even such utility stuff as printing output (print operator in perl) first class citizens of languages. By doing this, they bring a lot of garbage to language axiomatics. Why the heck I can't import a function that does printing or function composition from some module or namespace?

Idea of Rio is to get rid of how much out-of-the-box-syntax-stuff as possible and to give programmer a freedom to define his own operators and stuff. This freedom gives you a possibility to create your own pretty internal DSL's.

For example:

value <| is function of (fn, v) do fn(v) end
values result is do_some_more_complex_stuff '<|' do_complex_stuff '<|' do_stuff '<|' 4

That's all, you had to write just a single line of code to be able to use f-sharp's pipe operator. But in exchange, you've got a possibility to define any operator you wish by just creating a function.

value >>> is function of (value) do log(value) end
>>>' "Hello, world"

For now Rio has build-in arithmetical operators. Currently they are global, since modules are not supported yet, but in future I'm gonna move them to separate module, so that client will need to import them explicitly, like:

use Math from "Math"

Operators in rio are just functions and should be called in a lisp manner:

sum(div(2, 32), 0)

Or via infix notation:

2 'div' 32 'sum' 0

Attention, since arithmetical operators are just functions, mathematical operator precendence is not preserved. Infix function calls are right-asssociative. So expression above will be calculated like this 2 / (32 + 0)

Constant declaration

Variables in Rio are immutable. To not confuse novice programmers with false expectation of variable reassigment possibility, there's no assignment operator. Instead there's is, i.e:

value name is "Simon"

We're just stating that something is something else.

Lambdas

Functions in rio are high order, meaning they are data, as well as numbers, strings, etc. We can declare a function with function of (arg, ...args) do ... end notation. Result of function invocation is the last expression inside it's body (yay, just like in ruby; btw function declaration syntax is prety similar to what we have in ruby)

For example:

value greet is function of (name) do
  "Hello " 'concat' name 'concat' "!"
end

In example above you can notice, that strings are concatenated with something, which is called concat and is enclosed in single quotes. concat is just some function, which accepts two string arguments and concatenate them. 'concat' is a special syntax for infix function invocation. Any function which accepts two arguments can be invoked in this manner.

value somehow_affected_by is function of (a, b) do
  div(sum(a, b), 2)
end

value result is 3 'somehow_affected_by' 4

> 3.5

Prefix notation is supported as well:

value increment is function of (n) do
  n '+' 1
end

value incremented_five is increment' 5

> 6

Lists

There are lists. List literals are similar to ones in js. There are length, head, tail and concat functions for manipulating them. You can see example of basic lists usage below:

value list is [1, 2, 3]

value is_empty is function of (list) do
  length' list 'equals' 0
end

value map is function of (list, fn) do
  if is_empty' list
    then list
    else [fn' head' list] 'concat' (tail' list 'map' fn)
end

value increment is function of (n) do n '+' 1 end

[1, 2, 3, 4, 5, 6] 'map' increment

Todos

• Introduce namespaces
• Implement basic data structures