Therl

Truly Human Readaby Language
(Yes, the acronym is a little cursed. I know.)

Therl is a human-readable, instruction-based programming language written entirely in pure Python. Its goal is to make code read almost like plain English while remaining predictable and easy to parse.

set greeting to "hello"

func greet <name>

    say greeting + " " + name + "!"

end

func main

    run greet with <name> as "Jeff"

    set numbers to [1..10]

    say numbers

end

run main

Output:

hello Jeff!
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

---

Features

• 📖 Human-readable syntax
• 📝 Instruction-based language design
• 🐍 Written entirely in pure Python
• 🔄 Strictly dynamically typed variables
• 📦 Built-in lists
• 🔢 Integer, float, string and boolean types
• 🧩 Functions with named parameters
• 📢 Simple say statement for output
• ✏️ Mutable list elements
• 🔀 Conditional statements with if, else if, and else
• 🚀 Easy to extend

---

Example

set greeting to "hello"

func greet <name>

    say greeting + " " + name + "!"

end

func main

    say "Welcome!"

    run greet with <name> as "Jeff"

    set ids to [1..10]

    say ids

    set ids at 0 to 1000

    say ids

    add 10 to ids

    say ids

end

run main

Output:

Welcome!
hello Jeff!
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
[1000, 2, 3, 4, 5, 6, 7, 8, 9, 10]
[1000, 2, 3, 4, 5, 6, 7, 8, 9, 10, 10]

---

Conditional Statements

Therl supports if and else for conditional logic:

set name to "bob"

if name == "bob"
    say "Go away bob!"
else

    say "Hello " + name

end

Output:

Go away bob!

---

Installation

Therl requires Python 3.10 or newer.

Install the latest release from PyPI:

python -m pip install therl

Run a Therl program:

therl hello.therl

or

python -m therl hello.therl

---

Project Status

⚠️ Therl is currently in active development.

Expect missing features, breaking changes, and plenty of experimentation as the language evolves.

---

Roadmap

• Arithmetic expressions
• Error reporting with line numbers
• Conditional statements
• Loops
• Modules
• Dictionaries / Maps
• Standard library

---

Why?

Because making programming languages is fun.

And because writing

set score to 100

add 10 to score

say score

just feels oddly satisfying.

---