tricu/README.md

# tricu

## Introduction

tricu (pronounced like "tree-shoe" in English) is a purely functional interpreted language implemented in Haskell. [I'm](https://eversole.co) developing tricu to further research the possibilities offered by the various forms of [Tree Calculi](https://github.com/barry-jay-personal/typed_tree_calculus/blob/main/typed_program_analysis.pdf).

tricu offers minimal syntax sugar yet manages to provide a complete, intuitive, and familiar programming environment. There is great power in simplicity. tricu offers:

1. `t` operator behaving by the rules of Tree Calculus
1. Function definitions/assignments
1. Lambda abstractions eliminated to Tree Calculus forms
1. List, Number, and String literals
1. Parentheses for grouping function application

These features move us cleanly out of the [turing tarpit](https://en.wikipedia.org/wiki/Turing_tarpit) territory that you may find yourself in if you try working only with the `t` operator.

tricu is the word for "tree" in Lojban: `(x1) is a tree of species/cultivar (x2)`. This project was named "sapling" until I discovered the name is already being used for other (completely unrelated) programming language development projects.

## What does it look like?

```
-- Anything after `--` on a single 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) -- `id` evaluates to the TC form of: t (t (t t)) t
triage = (\a b c : t (t a b) c)
-- Intensionality! We can inspect program structure, not just inputs/outputs:
test = triage "Leaf" (\_ : "Stem") (\_ _ : "Fork")

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

## Installation and Use

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

- Quick Start (REPL): 
  - `nix run git+https://git.eversole.co/James/tricu`
- Build executable in `./result/bin`: 
  - `nix build git+https://git.eversole.co/James/tricu`

`./result/bin/tricu --help`

```
tricu Evaluator and REPL

tricu [COMMAND] ... [OPTIONS]
  tricu: Exploring Tree Calculus

Common flags:
  -? --help           Display help message
  -V --version        Print version information

tricu [repl] [OPTIONS]
  Start interactive REPL

tricu eval [OPTIONS]
  Evaluate a file and return the result of the expression in the final line

  -f --file=FILE      Optional input file path for evaluation.
                      Defaults to stdin.
  -o --output=OUTPUT  Optional output file path for resulting output.
                      Defaults to stdout.
  -t --form=FORM      Optional output form: (fsl|tree|ast|ternary|ascii).
                      Defaults to fsl.

tricu decode [OPTIONS]
  Decode a Tree Calculus value into a string representation

  -f --input=ITEM     Optional file path to attempt decoding.
                      Defaults to stdin.
```

## 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 tricu sounds interesting but compiling this repo sounds like a hassle, you should check out his site.