Nim

The Nim crown logo
Paradigms	Multi-paradigm: compiled, concurrent, Procedural, Imperative, Functional, Object-oriented
Designed by	Andreas Rumpf
First appeared	2008; 12 years ago (2008)
Stable release	1.4.2[1]  / 1 December 2020; 30 days ago (1 December 2020)
Typing discipline	Static,[2] strong,[3] inferred, structural
Platform	IA-32, x86-64
OS	Cross-platform[4]
License	MIT[5][6]
Filename extensions	.nim, .nims, .nimble
Website	nim-lang.org
Influenced by
Ada, Modula-3, Lisp, C++, Object Pascal, Python, Oberon

Nim is an imperative, general-purpose, multi-paradigm, statically typed, systems, compiled programming language^[7] designed and developed by Andreas Rumpf. It is designed to be "efficient, expressive, and elegant",^[8] supporting metaprogramming, functional, message passing,^[5] procedural, and object-oriented programming styles by providing several features such as compile time code generation, algebraic data types, a foreign function interface (FFI) with C, C++, Objective-C, and JavaScript, as well as supporting compiling to C, C++, Objective-C, and JavaScript.

Description

Nim was created to be a language as fast as C, as expressive as Python, and as extensible as Lisp.

Nim is statically typed.^[9] It supports compile-time metaprogramming features such as syntactic macros and term rewriting macros.^[10] Term rewriting macros enable library implementations of common data structures, such as bignums and matrices, to be implemented efficiently, as if they were built-in language facilities.^[11] Iterators are supported and can be used as first class entities,^[10] as can functions, allowing for the use of functional programming methods. Object-oriented programming is supported by inheritance and multiple dispatch. Functions can be generic, they can be overloaded, and generics are further enhanced by Nim's support for type classes. Operator overloading is also supported.^[10] Nim includes tunable automatic garbage collection based on deferred reference counting with cycle detection, which can also be turned off altogether.^[12]

In 2014, Andrew Binstock (editor-in-chief of Dr. Dobb's Journal) said:

"[Nim] ... presents a most original design that straddles Pascal and Python and compiles to C code or JavaScript."^[13]

Today, Nim compiles to C, C++, JavaScript, and Objective-C.

History

Nim's initial development was started in 2005 by Andreas Rumpf. It was originally named Nimrod when the project was made public in 2008.^[15] The first version of the Nim compiler was written in Pascal using the Free Pascal compiler.^[16] In 2008, a version of the compiler written in Nim was released.^[17] The compiler is free and open-source software, and is being developed by a community of volunteers working with Andreas Rumpf.^[18] The language was officially renamed from Nimrod to Nim with the release of version 0.10.2 in December 2014.^[19] On the 23rd of September, 2019, version 1.0.0 of Nim was released, signifying the maturation of the language and its toolchain.

Language design

Syntax

The syntax of Nim resembles that of Python.^[20] Code blocks and nesting statements are identified through use of white-space, according to the offside-rule. Many keywords are identical to their Python equivalents, which are mostly English keywords, whereas other programming languages usually use punctuation. This makes transitioning from coding Python to coding Nim easy and painless. With the goal of improving upon its influence languages, even though Nim supports indentation-based syntax like Python, it introduced additional flexibility; one may break statements with a comma or binary operator to the next line. Additionally, Nim supports user-defined operators.

Nim is almost fully style-insensitive; two identifiers are considered equal if they only differ by capitalization and underscores, as long as the first characters are identical. Historically, Nim was fully case-insensitive (meaning that capitalization and underscores of the identifiers were fully ignored).^[21]

Influence

Nim was influenced by specific characteristics of existing languages, including the following:

• Modula-3: traced vs untraced pointers
• Object Pascal: type safe bit sets (set of char), case statement syntax, various type names and filenames in the standard library
• Ada: subrange types, distinct type, safe variants – case objects
• C++: operator overloading, generic programming
• Python: Off-side rule
• Lisp: Macro system, embrace the AST, homoiconicity
• Oberon: export marker
• C#: async – await, lambda macros
• Go: defer

Uniform Function Call Syntax

Nim supports Uniform Function Call Syntax (UFCS)^[22] and identifier equality, which provides a large degree of flexibility in use.

For example, each of these lines does the same call, just with different syntax:

echo "hello world"
echo("hello world")
"hello world".echo()
"hello world".echo
"hello".echo(" world")
"hello".echo " world"

Identifier Equality

Except for the first letter, identifiers in Nim are compared in a case-insensitive manner, and underscores are ignored.

Example:

const useHttps = true
assert useHttps == useHttps
assert useHTTPS == useHttps
assert use_https == useHttps

Stropping

Stropping is a method to explicitly mark a letter sequence for a special purpose. Stropping is not used in most modern languages, as keywords are usually reserved words, and thus, cannot be used as identifiers for variables or functions. The stropping method allows the same letter sequence to be used both as a keyword and as an identifier, which simplifies parsing and allows greater flexibility. An example of stropping is the ability to define a variable named if, without clashing with the keyword if. Nim's implementation of this is achieved via backticks, allowing any reserved word to be used as an identifier.^[23]

type Type = object
  `int`: int

let `object` = Type(`int`: 9)
assert `object` is Type
assert `object`.`int` == 9

var `var` = 42
let `let` = 8
assert `var` + `let` == 50

const `assert` = true
assert `assert`

Compiler

The Nim compiler outputs fast, optimized C code by default. It defers compiling-to-object code to an external C compiler^[24] to leverage existing compiler optimization and portability. Many C compilers are supported, including Clang, and GNU Compiler Collection (GCC). The Nim compiler can also output C++, Objective-C, and JavaScript code to allow easy interfacing with APIs written in those languages;^[7] developers can simply write in Nim, then compile to any supported language. Notably, this also allows writing applications for iOS and Android. There is also an unofficial LLVM backend, allowing use of the Nim compiler in a stand-alone way.^[25]

The Nim compiler is self-hosting, meaning it is written in the Nim language.^[26] The compiler supports cross-compilation, so it is able to compile software for any of the supported operating systems, no matter the development machine. This is useful for compiling applications for embedded systems, as well as uncommon computer architectures.

Speed

Speed is a primary goal of Nim's development. Despite Nim's easy and expressive Python-like syntax, benchmark tests demonstrate how competitively the language runs. In various community tests, Nim outperformed many languages that hold well-established reputations for being fast, including Rust, Go, and Kotlin.^[27][28][29] Remarkably, Nim is competitive with C itself in speed, executing quicker on a number of the benchmark tests.^[30] Nim executed faster than Python by large margins in virtually every example, usually by 300+ seconds. Important to note, most of these benchmark tests didn't even utilize Nim's optimization flags during compilation.

Nim can be utilized for speed even when it isn't the primary language of a project. Community tooling has allowed a strong working relationship between Python and Nim; wrappers exist to import Nim scripts in Python, and vice-versa.^[31] This relationship allows for Nim's speed to be harnessed by Python in the form of Nim modules imported in place of native Python modules.

When developing any Nim code where speed is paramount, it is vital that the --opt:speedflag be used, so as to render an executable most representative of Nim's capabilities.^[32]

Tools

Bundled Tools

The following tools are bundled with the Nim install package:

Nimble

Nimble is the standard package manager used by Nim to package Nim modules.^[33] It was initially developed by Dominik Picheta, who is also a core Nim developer. Nimble has been included as Nim's official package manager since Oct 27, 2015, the v0.12.0 release.^[34]

Nimble packages are defined by .nimble files, which contain information about the package version, author, license, description, dependencies, and more.^[35] These files support a limited subset of the Nim syntax called NimScript, with the main limitation being the access to the FFI. These scripts allow changing of test procedure, or for custom tasks to be written.

The list of packages is stored in a JSON file which is freely accessible in the nim-lang/packages repository on GitHub. This JSON file provides Nimble with a mapping between the names of packages and their Git or Mercurial repository URLs.

Because Nimble comes with the Nim compiler, it is possible to test the Nimble environment by running: nimble -v. This command will reveal the version number, the compilation date and time, as well as the git hash of nimble. Nimble utilizes the git package, which must be available for Nimble to function properly. The Nimble command-line is used as an interface for installing, removing (uninstalling), and upgrading/patching module packages.^[36]

c2nim

c2nim is a transcompiler/transpiler that helps to generate new bindings by translating ANSI C code to Nim code.^[37] The output is human-readable Nim code that is meant to be tweaked by hand after the translation process.

DrNim

DrNim is a tool that combines the Nim compiler Frontend with the Z3 proof engine in order to allow verify and validate software written in Nim. Nim comes with DrNim source code included, but requires compilation using Koch, also bundled with Nim.

Koch

A maintenance script that is used to build Nim, as well as provide HTML documentation.

Nimgrep

Nimgrep is a generic tool for manipulating text. It is used to search for regex, peg patterns, and contents of directories, and it can be used to replace tasks.

Nimsuggest

Nimsuggest is a tool that helps any source code editor query a .nim source file to obtain useful information like definition of symbols or suggestions for completions.

Niminst

Niminst is a tool to generate an installer for a Nim program. It creates .msi installers for Windows via Inno Setup, as well as install/uninstall scripts for Linux, Mac, and BSD.

Nimpretty

Nimpretty is a Nim source code beautifier, used to format code according to the official style guide.

Testament

Testament is an advanced automatic Unittests runner for Nim tests. Used for the development of Nim itself, it offers process isolation tests, generates statistics about test cases, supports multiple targets and simulated Dry-Runs, has logging, can generate HTML reports, can skip tests from a file, and more.

Other Notable Tools

The following are some notable tools that aren't included in the Nim package:

Choosenim

Choosenim was developed by Dominik Picheta, creator of the Nimble package manager, as a tool to enable developers to have multiple versions of the Nim compiler installed. Choosenim downloads any Nim stable or development compiler version from the command line, enabling easy switching between them.^[38]

Nimfix

Nimfix is a tool that helps to convert old-style Nimrod code to Nim code.^[39] Nimfix is currently in beta.^[40]

pas2nim

pas2nim is a tool to translate Object Pascal wrappers to Nim code.^[41] pas2nim played an important role in Nim's timeline, as it was used to translate the original Pascal sources of the Nim compiler. Only what maps easily to Nim is supported; Free Pascal, Delphi-style classes are unsupported, as are some other hard-to-translate features. As of late 2020, development and maintenance on pas2nim is mostly stalled.

py2nim

py2nim is a tool used for transpiling Python code into idiomatic Nim code.^[42] Currently its development is stalled.

Standard Library

The Nim standard library can be classified into two groups, known as pure and impure libraries.

Pure Libraries

A collection of modules written only in Nim, pure libraries do not include wrappers to access libraries written in other programming languages. The pure modules can be further classified into subgroups based on their tasks, which include the following:

• The Core
• Collections and Algorithms
• String Handling
• Generic Operating System Services
• Math Libraries
• Internet Protocols
• Parsers

Impure Libraries

The impure modules of Nim code which depend on external libraries that are written in other programming languages such as C.

Libraries

A Nim program can use any library which can be used in a C, C++ and JavaScript program. Language bindings exist for many libraries, including GTK+, Qt QML,^[43] wxWidgets,^[44] SDL2, Cairo, OpenGL, WinAPI, zlib, libzip, OpenSSL, Vulkan^[45] and cURL.^[46] Nim works with PostgreSQL, MySQL and SQLite databases. Nim can interface with the Lua,^[47] Julia,^[48] Rust,^[49] C Sharp,^[50] TypeScript,^[51] and Python^[52] programming languages.

Examples

Hello world

The "Hello, World!" program in Nim:

echo("Hello, world!")
# Procedures can be called with no parentheses
echo "Hello, World!"

Another version of making a "Hello World" is...

stdout.write("Hello, world!\n")

Factorial

Program to calculate the factorial of a positive integer using the iterative approach:

import strutils

var n = 0
try:
  stdout.write "Input positive integer number: "
  n = stdin.readline.parseInt
except ValueError:
  raise newException(ValueError, "You must enter a positive number")

var fact = 1
for i in 2..n:
  fact = fact * i

echo fact

Using the module math from Nim's standard library:

import math
echo fac(x)

Reversing a string

A simple demonstration showing many of Nim's features.

func reverse(s: string): string =
  for i in countdown(s.high, 0):
    result.add s[i]

let str1 = "Reverse This!"
echo "Reversed: ", reverse(str1)

One of the more exotic features is the implicit result variable. Every procedure in Nim with a non-void return type has an implicit result variable that represents the value that will be returned. In the for loop we see an invocation of countdown which is an iterator. If an iterator is omitted, the compiler will attempt to use an items iterator, if one is defined for the type specified.

Graphical user interface

Using GTK3 with gobject introspection through the gintro module:

import gintro/[gtk, glib, gobject, gio]

proc appActivate(app: Application) =
  let window = newApplicationWindow(app)
  window.title = "GTK3 application with gobject introspection"
  window.defaultSize = (400, 400)
  showAll(window)

proc main =
  let app = newApplication("org.gtk.example")
  connect(app, "activate", appActivate)
  discard run(app)

main()

This code requires the gintro module to work, which is not part of the standard library. To install the module gintro and many others you can use the tool nimble, which comes as part of nim. To install the gintro module with nimble you do the following:

nimble install gintro

Programming Paradigms

Object Oriented Programming (OOP)

Metaprogramming

Template

This is an example of metaprogramming in Nim using its template facilities.

template genType(name, fieldname: untyped, fieldtype: typedesc) =
  type
    name = object
      fieldname: fieldtype

genType(Test, foo, int)

var x = Test(foo: 4566)
echo(x.foo) # 4566

The genType is invoked at compile-time and a Test type is created.

Generic

Generics may be used in procedures, templates and macros. They are defined after the proc's name in square brackets, as seen below.

proc addThese[T](a, b: T): T =
  a + b

echo addThese(1, 2) # 3 (of int type)
echo addThese(uint8 1, uint8 2) # 3 (of uint8 type)

In addThese, T is the generic type, the compiler will accept any values for this function as long as both parameters and the return value are of the same type.

One can further clarify which types the procedure will accept by specifying a type class.^[53]

proc addTheseNumbers[T: SomeNumber](a, b: T): T =
  a + b

addTheseNumberswill then only work for types contained in the SomeNumbersum type.

Macros

Macros can literally rewrite parts of the code before it's compiled. Nim macros are powerful and can do many operations on the abstract syntax tree.

Here's a simple example, that creates a macro called twice:

import macros

macro twice(arg: untyped): untyped =
  result = quote do:
    `arg`
    `arg`

twice echo "Hello world!"

The twice macro in this example takes the echo statement in the form of an abstract syntax tree as input. In this example we decided to return this syntax tree without any manipulations applied to it. But we do it twice, hence the name of the macro. The end result is that the code gets rewritten by the macro to look like the following code at compile time:

echo "Hello world!"
echo "Hello world!"

Foreign Function Interface (FFI)

Nim's FFI is used to call functions written in the other programming languages that it can compile to. This means that libraries written in C, C++, Objective-C and JavaScript can be used in the Nim source code. One should be aware that both JavaScript and C, C++, or Objective-C libraries cannot be combined in the same program, as they are not as compatible with JavaScript as they are with each other. Both C++ and Objective-C are based on and compatible with C, but JavaScript is incompatible, as a dynamic, client-side web-based language.^[54]

The following program demonstrates the ease with which external C code can be used directly in Nim.

proc printf(formatstr: cstring) {.header: "<stdio.h>", varargs.}

printf("%s %d\n", "foo", 5)

In this code the printf function is imported into Nim and then used.

Basic example using 'console.log' directly for the JavaScript compilation target:

proc log(args: any) {.importjs: "console.log(@)", varargs.}
log(42, "z", true, 3.14)

The JavaScript code produced by the Nim compiler can be executed with Node.js or a web browser.

Parallelism

To activate threading support in Nim, a program should be compiled with --threads:on command line argument. Each thread has a separate garbage collected heap and sharing of memory is restricted, which helps with efficiency and stops race conditions by the threads.

import locks

var
  thr: array[0..4, Thread[tuple[a,b: int]]]
  L: Lock

proc threadFunc(interval: tuple[a,b: int]) {.thread.} =
  for i in interval.a..interval.b:
    acquire(L) # lock stdout
    echo i
    release(L)

initLock(L)

for i in 0..high(thr):
  createThread(thr[i], threadFunc, (i*10, i*10+5))
joinThreads(thr)

Nim also has a channels module that simplifies passing data between threads.

import os

type
  CalculationTask = object
    id*: int
    data*: int

  CalculationResult = object
    id*: int
    result*: int

var task_queue: Channel[CalculationTask]
var result_queue: Channel[CalculationResult]

proc workerFunc() {.thread.} =
  result_queue.open()

  while true:
    var task = task_queue.recv()
    result_queue.send(CalculationResult(id: task.id, result: task.data * 2))

var workerThread: Thread[void]
createThread(workerThread, workerFunc)

task_queue.open()
task_queue.send(CalculationTask(id: 1, data: 13))
task_queue.send(CalculationTask(id: 2, data: 37))

while true:
  echo "got result: ", repr(result_queue.recv())

Concurrency

Nim supports asynchronous IO via the asyncdispatch module, which adds async/await syntax via the macro system. An example of an asynchronous http server:

import asynchttpserver, asyncdispatch

var server = newAsyncHttpServer()
proc cb(req: Request) {.async.} =
  await req.respond(Http200, "Hello World")

waitFor server.serve(Port(8080), cb)

Nim Community

Nim has an active community on the self-hosted, self-developed official forum.^[55] Additionally, the project uses a Git repository, bug tracker, and wiki hosted by GitHub where the community engages with the language.^[56]

Conventions

The first Nim conference, NimConf, took place on June 20, 2020. The conference was held digitally due to COVID-19, with an open call for contributor talks in the form of YouTube videos.^[57] The conference began with language overviews by Nim developers Andreas Rumpf and Dominik Picheta. Presentation topics included talks about Nim web frameworks, mobile development, IoT devices, and game development, including a talk about writing Nim for Game Boy Advance.^[58] NimConf 2020 is available as a YouTube playlist.^[59]

In addition to official conferences, Nim has been featured at various other conventions. A presentation on Nim was given at the O'Reilly Open Source Convention (OSCON) in 2015.^[60][61][62] Four speakers represented Nim at FOSDEM 2020, including the creator of the language, Andreas Rumpf.^[63]

See also

• Crystal (programming language)
• D (programming language)
• Go (programming language)
• Rust (programming language)

References

External links

• Official website
• Nim on GitHub
• Information about Nim on Stack Overflow