# sapling

## Introduction

sapling is a "micro-language" that [I'm](https://eversole.co) working on to investigate [Tree Calculus](https://github.com/barry-jay-personal/typed_tree_calculus/blob/main/typed_program_analysis.pdf) .

It offers a minimal amount of syntax sugar yet provides a complete and intuitive programming environment. Sapling offers:

- `t` operator behaving by the rules of Tree Calculus
- Function ("variable") definitions
- Lambda abstractions
- List, Number, and String literals

## What does it look like?

```
-- Anything after `--` on a line is a comment
-- We can define functions or "variables" as tree calculus values
false = t 
_ = t
true = t t
-- We can define functions as lambda expressions that are eliminated to tree
-- calculus terms.
id = (\a : a) -- t (t (t t)) t
triage = (\a b c : t (t a b) c) 
triage = (\a b c : t (t a b) c)
-- Intensionality !!!
test = triage "Leaf" (\_ : "Stem") (\_ _ : "Fork")

-- REPL
-- `sapling <` is the input prompt
-- `sapling >` is the Tree Calculus form output. Most are elided below.
-- `DECODE -:` is an attempt to interpret the TC output as strings/numbers.
sapling < test t
sapling > Fork (Fork Leaf (Fork ...) ... ) 
DECODE -: "Leaf"
sapling < test (t t)
DECODE -: "Stem"
sapling < test (t t t)
DECODE -: "Fork"
sapling < map (\i : listConcat i " is super cool!") [("He") ("She") ("Everybody")]
DECODE -: ["He is super cool!", "She is super cool!", "Everybody is super cool!"]
```

## Installation

You can easily build and/or run this project using [Nix](https://nixos.org/download/).

- Build REPL binary: `nix build git+https://git.eversole.co/James/sapling`
- Run REPL: `nix run git+https://git.eversole.co/James/sapling`

## Acknowledgements 

Tree Calculus was discovered by [Barry Jay](https://github.com/barry-jay-personal/blog). 

[treecalcul.us](https://treecalcul.us) is an excellent website with an intuitive playground created by [Johannes Bader](https://johannes-bader.com/) that introduced me to Tree Calculus. If sapling sounds interesting but compiling this repo sounds like a hassle, you should check out his site.