Thusly

Programming Language

Developer

Elle J

C

Parser

Compiler

Bytecode

VM

Thusly is an open-source general-purpose programming language originally developed for personally deepening my knowledge of compilers, virtual machines, and the C language. The implementation is a one-pass compiler using operator-precedence parsing and a stack-based virtual machine.

👉️ Thusly is currently being developed. See Milestones for implemented features.

Playground
Language
Milestones

Playground

Try out Thusly in the interactive playground.

Language

Characteristics

General-purpose
Interpreted
Dynamically typed
Imperative
Garbage collected

Syntax

The following is a subset of the language:

Variables, Data Types, and Literals

const id: 100
var valid: true
var enabled: false
var nickname: none
nickname: "Alex"

Selection

var age: 30

if age in 25..35
    @out("You are young")
end

var timeLeft: 120
var cancelled: false

if timeLeft = 0 or cancelled
    @out("Done")
elseif timeLeft < 60
    @out("Almost done")
else
    @out("Keep going")
end

Loop

foreach value in 0..10
    @out(value)
end

var a: 0
var b: 10
var c: 2

foreach value in a..b step c
    @out(value)
end

var i: 0

while i < 10 {i +: 1}
    @out(i)
end

Whitespace is semantically insignificant except for newline characters on non-blank lines.

Design

To read about the architectural design, implementation details, and follow along walk-throughs of examples of tokenization, parsing, compilation, evaluation, and execution, see the design documentation on GitHub.

Milestones

Milestone 1: Support arithmetic, comparison, and equality operations

✅ The terminals in the initial grammar can be identified from user input via a multi-line file or single-line REPL input and then tokenized.
✅ Arithmetic expressions using number (double) can be evaluated.
- ✅ Addition (+)
- ✅ Subtraction (-)
- ✅ Multiplication (*)
- ✅ Division (/)
- ✅ Modulo (mod)
- ✅ Unary negation (-)
- ✅ Precedence altering (())
✅ Comparison expressions using number can be evaluated.
- ✅ Greater than (>)
- ✅ Greater than or equal to (>=)
- ✅ Less than (<)
- ✅ Less than or equal to (<=)
✅ Equality and logical negation expressions using number, boolean, text (string), and none can be evaluated.
- ✅ Equal to (=)
- ✅ Not equal to (!=)
- ✅ Logical not (not)
✅ Concatenation of text literals using + can be evaluated.

Milestone 2: Support variables and control flow

✅ Temporary @out statement can be executed.
✅ Global and local variables can be defined and used.
- ✅ Declaration and initialization (var <name> : <expression>)
- ✅ Assignment expression (<name> : <expression>)
✅ Variables adhere to lexical scope.
- ✅ Standalone block
```
block
    <statements>
end
```
✅ Logical operators can be evaluated.
- ✅ Conjunction (and)
- ✅ Disjunction (or)

⭕ Control flow statements can be executed.

⭕ Selection
- ✅ if
- ⭕ elseif
- ✅ else

if <condition>
    <statements>
elseif <condition>
    <statements>
else
    <statements>
end

✅ Loops
- ✅ Bounded (foreach)

foreach <name> in <start>..<end> step <change>
    <statements>
end

Example 1

// `<change>` expression is implicitly 1
foreach value in 0..10
    @out value
end

Example 2

var a: 0
var b: 10
var c: 2
foreach value in a..b step c
    @out value
end

✅ Unbounded (while)

while <condition> { <change> }
    <statements>
end

Example

// `<change>` expression is optional
var i: 0
while i < 10 {i +: 1}
    @out i
end

⭕ Augmented assignment expressions can be evaluated.
- ✅ Addition and assignment (+:)
- ✅ Subtraction and assignment (-:)
- ✅ Multiplication and assignment (*:)
- ⭕ Division and assignment (/:)
- ⭕ Modulo and assignment (mod:)
⭕ Range comparison expression can be evaluated (<value> in <min>..<max>)

More milestones will be added.

Milestone 3: Provide an interactive playground

✅ A Thusly VM can run and execute code in the browser via an interactive playground.

Milestone 4: Support first-class functions

⭕ Functions can be defined and invoked.
⭕ Closures are supported.
⭕ Functions are first-class citizens.