# 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?

```
tricu < -- Anything after `--` on a single line is a comment
tricu < id = (\a : a) -- Lambda abstraction is eliminated to tree calculus terms
tricu < head (map (\i : lconcat i " world!") [("Hello, ")])
tricu > "Hello,  world!"
tricu < id (head (map (\i : lconcat i " world!") [("Hello, ")]))
tricu > "Hello,  world!"

tricu < -- Intensionality! We can inspect the structure of a function.
tricu < triage = (\a b c : t (t a b) c)
tricu < test = triage "Leaf" (\z : "Stem") (\a b : "Fork")
tricu < test t t
tricu > "Stem"
tricu < -- We can even write a function to convert a function to source code
tricu < toTString id
tricu > "t (t (t t)) t"
```

## 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 tricu and return the result of the final expression.

  -f --file=FILE  Input file path(s) for evaluation.
                    Defaults to stdin.
  -t --form=FORM  Optional output form: (tree|fsl|ast|ternary|ascii).
                    Defaults to tricu-compatible `t` tree form.

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

  -f --file=FILE  Optional input 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.