The Erg Programming Language


This is the main source code repository for Erg. This contains the compiler and documentation.

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Erg can be recommended to a person that:

Features

Some features are not yet implemented. Please see TODO.md for implementation status.

  1. Robustness

    Erg has a smart & powerful type system. For example, Erg can do null checking (Option type), division by zero, and out-of-range addresses in arrays at compile time.

    ```python rand = pyimport "random"

    l = [1, 2, 3] assert l in [Nat; 3] # type checking assert l in [1..3; 3] # more detailed l2 = l.push(rand.choice! 0..10) assert l2 in [0..10; 4] assert l2 + [3, 5, 7] in [0..10; 7]

    This causes an IndexError, Erg can detect it at compile time

    l2[10] # IndexError: l2 has 7 elements but was accessed the 11th element

    2.times! do!: print! "hello, ", end := ""

    => hello, hello,

    -2.times! do!: print! "hello, ", end := ""

    TypeError: .times! is a method of Nat (0 or more Int), not Int

    {Meter; Sec; meter; yard; sec; ...} = import "unit"

    velocity x: Meter, t: Sec = x / t

    v = velocity 3yard, 2sec # TypeError: the type of x was mismatched: expect Meter, found Yard v = velocity 3meter, 2sec # v == 1.5 m/s ```

  2. Simplicity

    Erg consists of a very simple syntax, which can significantly reduce the amount of code compared to other languages. However, its functionality is not inferior to them.

    Since the type inference system is powerful, you can code like a dynamically typed language.

    python fib 0 = 0 fib 1 = 1 fib n = fib(n - 1) + fib(n - 2) assert fib(10) == 55

    In Erg, there are very few things that are treated as special; there are no reserved words. even for and while expressions are just one of the subroutines, so this is possible.

    ```python loop! block = while! True, block

    equals to while! True, do! print! "hello"

    loop! do!: print! "hello" ```

  3. Functional & Object-oriented

    Erg is a pure object-oriented language. Everything is an object; types, functions, and operators are all objects. On the other hand, Erg is also a functional language. Erg requires some kinds of markers to be placed on code that causes side effects or changes internal state, which can localize the complexity of code. This will greatly improve the maintainability of your code.

    ```python

    Functional style (immutable), same as sorted(list) in Python

    immutarr = [1, 3, 2] assert immutarr.sort() == [1, 2, 3]

    Object-oriented style (mutable)

    mutarr = ![1, 3, 2] mutarr.sort!() assert mut_arr == [1, 2, 3] i = !1 i.update! old -> old + 1 assert i == 2

    Functions cannot cause side effects

    inc i: Int! = i.update! old -> old + 1

    SyntaxError: cannot call a procedural method in a function

    hint: only methods of mutable types can change the state of objects

    Code that uses a lot of side effects is redundant, so you will naturally write pure code

    Counter! = Inherit Int! Counter!. new i: Int = Self!::new !i inc! ref! self = self.update! old -> old + 1

    c = Counter!.new 1 c.inc!() assert c == 2 ```

  4. Interoperability

    Erg is internally compatible with Python and can import the Python API at zero cost.

    ```python

    using built-in Python modules

    math, time = pyimport "math", "time" {sin; pi; ...} = math

    using an external Python module

    Tqdm! = pyimport("tqdm").'tqdm'

    print! sin pi # 1.2246467991473532e-16 for! Tqdm!.'call'(0..99), i => time.sleep! 0.01 * i ```

  5. Readable Error Messages

    Erg emphasizes the readability of error messages; Erg is a programmer-friendly language, ~~unlike C++.~~

    python proc! x = l = [1, 2, 3] l.push!(x) l

    console Error[#12]: File example.er, line 3, in <module>::proc! 2│ l = [1, 2, 3] 3│ l.push!(x) ^^^^^ AttributeError: Array object has no attribute `.push!` hint: to update the internal state of an object, make it mutable by using `!` operator hint: `Array` has `push`, see https://erg-lang.github.io/docs/prelude/Array/##push for more information hint: `Array!` has `push!`, see https://erg-lang.github.io/docs/prelude/Array!/##push! for more information

Requirements

A Python3 interpreter is required. If it is already installed on your machine, no setup is required.

Installation

Installing by cargo (Rust package manager)

sh cargo install erg

By enabling the --features flag, you can change the language in which error messages are displayed.

sh cargo install erg --features japanese

sh cargo install erg --features simplified_chinese

sh cargo install erg --features traditional_chinese

And more languages will be added (we are looking for translators. Please join the Translation Project).

sh cargo install erg --features debug

Building from source

Building from source code requires the Rust toolchain.

sh git clone https://github.com/erg-lang/erg.git cd erg cargo build --release

Building by Nix

If you've been installed Nix, the following command will be generate binary into result/bin/erg under the project.

sh git clone https://github.com/erg-lang/erg.git cd erg nix-build

If you've been enabled Nix Flakes.

sh git clone https://github.com/erg-lang/erg.git cd erg nix build

Contribution

Contributions are always welcome! To get started with contributions, please look CONTRIBUTING.md.

If you have any questions, please feel free to ask them on the Discord channel.

License

All files in the assets and doc folders are licensed with CC-BY-4.0. The rest of the files in this repository are licensed with Apache License 2.0 + MIT License.

For credits about third party crates, see THIRDPARTYCREDITS.md.