Nim (programming language)

Nim is statically typed.{{cite web |url=https://akehrer.github.io/posts/getting-started-with-nim |title=Nim Syntax |last=Kehrer |first=Aaron (akehrer) |website=GitHub |date=5 January 2015 |access-date=2015-01-05}} It supports compile-time metaprogramming features such as syntactic macros and term rewriting macros.{{cite web |url=https://nim-lang.org/docs/manual.html#term-rewriting-macros |title=Nim Manual |website=Nim-lang.org |access-date=2014-07-20}} Term rewriting macros enable library implementations of common data structures, such as bignums and matrices, to be implemented efficiently and with syntactic integration, as if they were built-in language facilities.{{cite web |url=https://thestrangeloop.com/sessions/nimrod-a-new-approach-to-meta-programming |archive-url=https://web.archive.org/web/20140713011227/https://thestrangeloop.com/sessions/nimrod-a-new-approach-to-meta-programming |url-status=dead |archive-date=2014-07-13 |title=Strangeloop Nim presentation |access-date=2015-04-30}} Iterators are supported and can be used as first class entities, 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 and overloaded, and generics are further enhanced by Nim's support for type classes. Operator overloading is also supported. Nim includes multiple tunable memory management strategies, including tracing garbage collection, reference counting, and fully manual systems, with the default being deterministic reference counting with optimizations via move semantics and cycle collection via trial deletion.{{Cite web |title=Nim's Memory Management |url=https://nim-lang.org/docs/mm.html |access-date=2023-08-17 |website=nim-lang.org}}{{blockquote|text=[Nim] ... presents a most original design that straddles Pascal and Python and compiles to C code or JavaScript.{{cite web|last=Binstock|first=Andrew|date=2014-01-07|title=The Rise And Fall of Languages in 2013|url=http://www.drdobbs.com/jvm/the-rise-and-fall-of-languages-in-2013/240165192|access-date=2018-10-08|website=Dr. Dobb's Journal}}

|author=Andrew Binstock, editor-in-chief of Dr. Dobb's Journal, 2014

}}

{{As of|2023|8}}, Nim compiles to C, C++, JavaScript, Objective-C,[https://nim-lang.org/docs/nimc.html Nim Compiler User Guide] and LLVM.

Andreas Rumpf is the designer and original implementer of Nim. He received a diploma in computer science from the University of Kaiserslautern-Landau, Germany. His research interests include hard realtime systems, embedded systems, compiler construction and artificial intelligence.{{Cite book |last=Andreas Rumpf |title=Mastering Nim: A complete guide to the programming language}}

[https://nim-lang.org Nim's] original website design by Dominik Picheta and Hugo Locurcio. Joseph Wecker created the Nim logo.

The Nim programming language is a concise, fast programming language that compiles to C, C++ and JavaScript. Nim's initial development was started in 2005 by Andreas Rumpf. It was originally named Nimrod when the project was made public in 2008.{{Cite book |last=Picheta |first=Dominik |year=2017 |title=Nim in Action |publisher=Manning Publications |isbn=978-1617293436}}{{rp|4–11}}

The first version of the Nim compiler was written in Pascal using the Free Pascal compiler.{{cite web |url=https://github.com/Araq/Nim/tree/ea1f1ec6d4d6c776eb0f81c2bebdd4cb4c817ebe/nim |title=Nim Pascal Sources |website=GitHub |access-date=2013-04-05}} In 2008, a version of the compiler written in Nim was released.{{cite web |url=http://nim-lang.org:80/news.html |title=News |website=Nim-lang.org |access-date=2016-06-11 |url-status=live |archive-url=https://web.archive.org/web/20160626002904/http://nim-lang.org/news.html |archive-date=2016-06-26}} The compiler is free and open-source software, and is being developed by a community of volunteers working with Andreas Rumpf.{{cite web |url=https://github.com/Araq/Nim/contributors |title=Contributors |website=GitHub |access-date=2013-04-05}} The language was officially renamed from Nimrod to Nim with the release of version 0.10.2 in December 2014.{{cite web |url=https://nim-lang.org/blog/2014/12/29/version-0102-released.html |title=Version 0.10.2 released |date=2014-12-29 |first=Dominik |last=Picheta |website=Nim-lang.org |access-date=2018-10-17}} On September 23, 2019, version 1.0 of Nim was released, signifying the maturing of the language and its toolchain. On August 1, 2023, version 2.0 of Nim was released, signifying the completion, stabilization of, and switch to the ARC/ORC memory model.{{Cite web |title=Nim v2.0 released |url=https://nim-lang.org/blog/2023/08/01/nim-v20-released.html |access-date=2023-08-17 |website=Nim Programming Language |language=en}}

The syntax of Nim resembles that of Python.{{cite web |url=https://www.infoworld.com/article/3157745/application-development/nim-language-draws-from-best-of-python-rust-go-and-lisp.html |title=Nim language draws from best of Python, Rust, Go, and Lisp |first=Serdar |last=Yegulalp |date=2017-01-16 |website=InfoWorld}} Code blocks and nesting statements are identified through use of whitespace, 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. With the goal of improving upon its influence languages, even though Nim supports indentation-based syntax like Python, it introduced additional flexibility. For example, a single statement may span multiple lines if a comma or binary operator is at the end of each line. Nim also supports user-defined operators.

Unlike Python, Nim implements (native) static typing. Nim's type system allows for easy type conversion, casting, and provides syntax for generic programming. Nim notably provides type classes which can stand in for multiple types, and provides several such type classes 'out of the box'. Type classes allow working with several types as if they were a single type. For example:

• openarray {{En dash}} Represents arrays of different sizes, sequences, and strings
• SomeSignedInt {{En dash}} Represents all the signed integer types
• SomeInteger {{En dash}} Represents all the Integer types, signed or not
• SomeOrdinal {{En dash}} Represents all the basic countable and ordered types, except of non integer number

This code sample demonstrates the use of typeclasses in Nim:

1. Let's declare a function that takes any type of number and displays its double
2. In Nim functions with side effect are called "proc"

proc timesTwo(i: SomeNumber) =

echo i * 2

1. Let's write another function that takes any ordinal type, and returns
2. the double of the input in its original type, if it is a number;
3. or returns the input itself otherwise.
4. We use a generic Type(T), and precise that it can only be an Ordinal

func twiceIfIsNumber[T: SomeOrdinal](i: T): T =

when T is SomeNumber: # A `when` is an `if` evaluated during compile time

result = i * 2 # You can also write `return i * 2`

else:

# If the Ordinal is not a number it is converted to int,

# multiplied by two, and reconverted to its based type

result = (i.int * 2).T

{{codett|lang=nim|echo twiceIfIsNumber(67) # Passes an int to the function}}

echo twiceIfIsNumber{{codett|lang=nim|(67u8) # Passes an uint8}}

{{codett|lang=nim|echo twiceIfIsNumber(true) # Passes a bool (Which is also an Ordinal)}}

According to the language creator, Nim was conceived to combine the best parts of Ada typing system, Python flexibility, and powerful Lisp macro system.{{Citation |title=Interview with Nim language creator Andreas Rumpf | date=9 March 2020 |url=https://www.youtube.com/watch?v=-9SGIB946lw |access-date=2023-10-15 |language=en}}

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, AST manipulation, homoiconicity
• Oberon: export marker
• C#: async/await, lambda macros
• ParaSail: pointer-free programming

Nim supports uniform function call syntax (UFCS){{Cite web |url=http://nim-lang.org/docs/manual.html#procedures-method-call-syntax |title=Nim Manual: Method call syntax |access-date=2018-10-12}} and identifier equality, which provides a large degree of flexibility in use.

For example, each of these lines print "hello world", just with different syntax:

echo "hello world"

echo("hello world")

"hello world".echo()

"hello world".echo

echo("hello", " world")

"hello".echo(" world")

"hello".echo " world"

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. This is to enable a mixture of styles across libraries: one user can write a library using snake_case as a convention, and it can be used by a different user in a camelCase style without issue.{{Cite web |title=Nim Manual: Identifier Equality |url=https://nim-lang.org/docs/manual.html#lexical-analysis-identifier-equality |access-date=2023-08-17 |website=nim-lang.org}}

const useHttps = true

assert useHttps == useHttps

assert useHTTPS == useHttps

assert use_https == useHttps

The stropping feature allows the use of any name for variables or functions, even when the names are reserved words for keywords. 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.{{cite web |url=https://github.com/nim-lang/Nim/wiki/Tips-and-tricks |title=Tips and tricks |last1=Picheta |first1=Dominik (dom96) |last2=Wetherfordshire |first2=Billingsly (fowlmouth) |last3=Felsing |first3=Dennis (def-) |last4=Raaf |first4=Hans (oderwat) |last5=Dunn |first5=Christopher (cdunn2001) |author6=wizzardx |date=2017-10-25 |website=GitHub |access-date=2018-10-17}}

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`

The Nim compiler emits fast, optimized C code by default. It defers compiling-to-object code to an external C compiler{{cite AV media |last=Rumpf |first=Andreas |url=http://www.infoq.com/presentations/nimrod |title=Nimrod: A New Approach to Metaprogramming |website=InfoQ |time=2:23 |date=2014-01-15 |access-date=2014-07-20}} to leverage existing compiler optimization and portability. Many C compilers are supported, including Clang, Microsoft Visual C++ (MSVC), MinGW, and GNU Compiler Collection (GCC). The Nim compiler can also emit C++, Objective-C, and JavaScript code to allow easy interfacing with application programming interfaces (APIs) written in those languages; developers can simply write in Nim, then compile to any supported language. 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.{{Citation|last=Sieka|first=Jacek|title=arnetheduck/nlvm|date=2020-07-18|url=https://github.com/arnetheduck/nlvm|access-date=2020-07-21}}

The Nim compiler is self-hosting, meaning it is written in the Nim language.{{Cite web |url=https://github.com/nim-lang/Nim#compiling |title=Nim Compiling |last=Rumpf |first=Andreas |date=2018-10-12 |website=GitHub |access-date=2018-10-17}} The compiler supports cross-compiling, 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, and for uncommon and obscure computer architectures.{{Citation needed|date=October 2023}}

By default, the Nim compiler creates a debug build.{{Cite web|url=https://nim-lang.org/docs/nimc.html#compiler-usage-configuration-files|title = Nim Compiler User Guide}}

With the option -d:release a release build can be created, which is optimized for speed and contains fewer runtime checks.

With the option -d:danger all runtime checks can be disabled, if maximum speed is desired.

Nim supports multiple memory management strategies, including the following:{{Cite web |title=Nim's Memory Management |url=https://nim-lang.org/docs/mm.html |access-date=2024-07-28 |website=nim-lang.org}}

• --mm:arc – Automatic reference counting (ARC) with move semantics optimizations, offers a shared heap. It offers fully deterministic performance for hard realtime systems.{{Cite web |title=Introduction to ARC/ORC in Nim |url=https://nim-lang.org/blog/2020/10/15/introduction-to-arc-orc-in-nim.html |access-date=2023-08-17 |website=Nim Programming Language |language=en}} Reference cycles may cause memory leaks: these may be dealt with by manually annotating {.acyclic.} pragmas or by using --mm:orc.
• --mm:orc – Same as --mm:arc but adds a cycle collector (the "O") based on "trial deletion".{{Cite web |title=ORC - Vorsprung durch Algorithmen |url=https://nim-lang.org/blog/2020/12/08/introducing-orc.html |access-date=2023-08-17 |website=Nim Programming Language |language=en}} The cycle collector only analyzes types if they are potentially cyclic.
• --mm:refc – Standard deferred reference counting based garbage collector with a simple mark-and-sweep backup GC in order to collect cycles. Heaps are thread-local.
• --mm:markAndSweep – Simple mark-and-sweep based garbage collector. Heaps are thread-local.
• --mm:boehm – Boehm based garbage collector, it offers a shared heap.
• --mm:go – Go's garbage collector, useful for interoperability with Go. Offers a shared heap.
• --mm:none – No memory management strategy nor a garbage collector. Allocated memory is simply never freed, unless manually freed by the developer's code.

As of Nim 2.0, ORC is the default GC.

Many tools are bundled with the Nim install package, including:

Nimble is the standard package manager used by Nim to package Nim modules.{{Cite web |url=https://github.com/nim-lang/nimble |title=Nimble |website=GitHub |access-date=2018-10-12}} 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.{{Cite web |url=https://github.com/nim-lang/Nim/commit/49d810f3410c19803f2d6fbfb3feb03e1fc13fee |title=Nim v0.12.0 release |website=GitHub |access-date=November 28, 2020}}

Nimble packages are defined by .nimble files, which contain information about the package version, author, license, description, dependencies, and more.{{rp|132}} 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 JavaScript Object Notation (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.

Nimble comes with the Nim compiler. Thus, it is possible to test the Nimble environment by running:

nimble -v.

This command will reveal the version number, compiling date and time, and Git hash of nimble. Nimble uses 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.{{rp|130–131}}

c2nim is a source-to-source compiler (transcompiler or transpiler) meant to be used on C/C++ headers to help generate new Nim bindings.{{Cite web |url=https://github.com/nim-lang/c2nim |title=c2nim |website=GitHub |access-date=2018-10-12}} The output is human-readable Nim code that is meant to be edited by hand after the translation process.

koch is a maintenance script that is used to build Nim, and provide HTML documentation.{{Cite web|title=Nim maintenance script|url=https://nim-lang.org/docs/koch.html|access-date=2021-11-16|website=nim-lang.org}}

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. It is included to assist with searching Nim's style-insensitive identifiers.{{Cite web|title=nimgrep User's manual|url=https://nim-lang.org/docs/nimgrep.html|access-date=2021-11-16|website=nim-lang.org}}

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.{{Cite web|title=Nim IDE Integration Guide|url=https://nim-lang.org/docs/nimsuggest.html|access-date=2021-11-16|website=nim-lang.org}}

niminst is a tool to generate an installer for a Nim program.{{Cite web|title=niminst User's manual|url=https://nim-lang.org/docs/niminst.html|access-date=2021-11-16|website=nim-lang.org}}

It creates .msi installers for Windows via Inno Setup, and install and uninstall scripts for Linux, macOS, and Berkeley Software Distribution (BSD).

nimpretty is a source code beautifier, used to format code according to the official Nim style guide.{{cite web|date=2021-10-19|title=Tools available with Nim|url=https://nim-lang.org/docs/tools.html|url-status=live|website=nim-lang.org |archive-url=https://web.archive.org/web/20150509003939/https://nim-lang.org/docs/tools.html |archive-date=2015-05-09 |access-date=2022-02-18}}

[https://nim-lang.github.io/Nim/testament.html Testament] is an advanced automatic unit tests runner for Nim tests. Used in developing Nim, 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.

Some notable tools not included in the Nim distribution include:

[https://github.com/dom96/choosenim choosenim] was developed by Dominik Picheta, creator of the Nimble package manager, as a tool to enable installing and using multiple versions of the Nim compiler. It downloads any Nim stable or development compiler version from the command line, enabling easy switching between them.{{cite web |url=https://github.com/dom96/choosenim |title=choosenim |website=GitHub |access-date=2018-10-12}}

[https://github.com/yglukhov/nimpy nimpy] is a library that enables convenient Python integration in Nim programs.{{Citation|last=Glukhov|first=Yuriy|title=nimpy|date=2021-11-12|url=https://github.com/yglukhov/nimpy|access-date=2021-11-16}}

[https://github.com/treeform/pixie pixie] is a feature-rich 2D graphics library, similar to Cairo or the Skia. It uses SIMD acceleration to speed-up image manipulation drastically. It supports many image formats, blending, masking, blurring, and can be combined with the [https://github.com/treeform/boxy boxy] library to do hardware accelerated rendering.

[https://github.com/nimterop/nimterop nimterop] is a tool focused on automating the creation of C/C++ wrappers needed for Nim's foreign function interface.{{Citation|title=nimterop/nimterop|date=2021-11-12|url=https://github.com/nimterop/nimterop|publisher=nimterop|access-date=2021-11-16}}

Pure libraries are modules written in Nim only. They include no wrappers to access libraries written in other programming languages.

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

The Nim standard library includes modules for all basic tasks, including:[https://nim-lang.org/docs/lib.html Nim Standard Library]

• System and core modules
• Collections and algorithms
• String handling
• Time handling
• Generic Operating System Services
• Math libraries
• Internet Protocols and Support
• Threading
• Parsers
• Docutils
• XML Processing
• XML and HTML code generator
• Hashing
• Database support (PostgreSQL, MySQL and SQLite)
• Wrappers (Win32 API, POSIX)

A Nim program can use any library which can be used in a C, C++, or JavaScript program. Language bindings exist for many libraries, including GTK,{{Citation|title=Installation|date=2021-09-25|url=https://github.com/nim-lang/gtk2|publisher=The Nim programming language|access-date=2021-11-16}}{{Citation|last=StefanSalewski|title=High level GTK4 and GTK3 bindings for the Nim programming language|date=2021-11-15|url=https://github.com/StefanSalewski/gintro|access-date=2021-11-16}} Qt QML,{{cite web |url=https://github.com/status-im/NimQml |title=NimQml |website=GitHub|date=10 November 2022 }} wxWidgets,{{cite web |url=https://github.com/PMunch/wxnim |title=WxNim |website=GitHub|date=29 November 2022 }} SDL 2,{{Citation|title=SDL2 for Nim|date=2021-10-26|url=https://github.com/nim-lang/sdl2|publisher=The Nim programming language|access-date=2021-11-16}}{{Citation|last=Arabadzhi|first=Vladimir|title=sdl2_nim 2.0.14.2|date=2021-11-15|url=https://github.com/Vladar4/sdl2_nim|access-date=2021-11-16}} Raylib,{{cite web |url=https://github.com/planetis-m/naylib |title=naylib |website=GitHub|date=28 July 2024 }} Godot,{{cite web |url=https://github.com/godot-nim |title=godot-nim |website=GitHub|date=28 July 2024 }} UE5,{{cite web |url=https://github.com/jmgomez/NimForUE |title=NimForUE |website=GitHub|date=28 July 2024 }} Cairo,{{Citation|title=Cairo|date=2021-10-05|url=https://github.com/nim-lang/cairo|publisher=The Nim programming language|access-date=2021-11-16}} OpenGL,{{Citation|title=opengl|date=2021-11-14|url=https://github.com/nim-lang/opengl|publisher=The Nim programming language|access-date=2021-11-16}} Vulkan,{{cite web |url=https://github.com/nimgl/vulkan |title=vulkan |website=GitHub|date=28 July 2024 }} WinAPI,{{Citation|last=Ward|title=Winim|date=2021-11-15|url=https://github.com/khchen/winim|access-date=2021-11-16}} zlib, libzip, OpenSSL and cURL.{{cite web |url=http://nim-lang.org/lib.html |title=Nim Standard Library |website=Nim documentation |access-date=2015-04-04 |url-status=dead |archive-url=https://web.archive.org/web/20150406053933/http://nim-lang.org/lib.html |archive-date=2015-04-06 }} Nim works with PostgreSQL, MySQL, and SQLite databases.

There are open source tools of various degree of support that can be used to interface Nim with Lua,{{cite web |url=https://github.com/jangko/nimLUA |title=nimLUA |last=Lim |first=Andri (jangko) |date=2018-10-17 |website=GitHub |access-date=2018-10-17}} Julia,{{cite web |date=24 August 2022 |title=NimJL |url=https://github.com/Clonkk/nimjl |website=GitHub}} Rust,{{cite web |url=https://github.com/arnetheduck/nbindgen |title=Nbindgen |website=GitHub|date=17 November 2022 }}

C#,{{cite web |url=https://github.com/kobi2187/cs2nim |title=cs2nim |website=GitHub|date=10 October 2022 }}

and Python{{Citation|last=Glukhov|first=Yuriy|title=yglukhov/nimpy|date=2020-07-20|url=https://github.com/yglukhov/nimpy|access-date=2020-07-21}} programming languages or transpile Nim to TypeScript.{{cite web |date=21 November 2022 |title=ts2nim |url=https://github.com/bung87/ts2nim |website=GitHub}}

The "Hello, World!" program in Nim:

echo("Hello, World!")

1. Procedures can be called with no parentheses

echo "Hello, World!"

Another version of "Hello World" can be accomplished by calling the write function with the stdout stream:

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

write(stdout, "Hello, World!\n")

Several implementations of the Fibonacci function, showcasing implicit returns, default parameters, iterators, recursion, and while loops:

proc fib(n: Natural): Natural =

if n < 2:

return n

else:

return fib(n-1) + fib(n-2)

func fib2(n: int, a = 0, b = 1): int =

if n == 0: a else: fib2(n-1, b, a+b)

iterator fib3: int =

var a = 0

var b = 1

while true:

yield a

swap a, b

b += a

Program to calculate the factorial of a positive integer using the iterative approach, showcasing try/catch error handling and for loops:

import std/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 std/math

echo fac(x)

A simple demonstration showing the implicit result variable and the use of iterators.

proc 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 Nim's 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 to 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.

Using GTK 3 with GObject introspection through the [https://github.com/StefanSalewski/gintro 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

Functional programming is supported in Nim through first-class functions and code without side effects via the noSideEffect pragma or the func keyword.{{Cite web|title=Nim Manual|url=https://nim-lang.org/docs/manual.html#procedures-func|access-date=2021-07-10|website=nim-lang.org}} Nim will perform side effect analysis and raise compiling errors for code that does not obey the contract of producing no side effects when compiled with the experimental feature strictFuncs, planned to become the default in later versions.{{Cite web |title=Nim Forum: Update on strict funcs |url=https://forum.nim-lang.org/t/9716 |access-date=2023-08-17 |website=forum.nim-lang.org}}

Contrary to purely functional programming languages, Nim is a multi-paradigm programming language, so functional programming restrictions are opt-in on a function-by-function basis.

Nim supports first-class functions by allowing functions to be stored in variables or passed anonymously as parameters to be invoked by other functions.{{Cite web |title=Nim by Example - First Class Functions |url=https://nim-by-example.github.io/procvars/}} The std/sugar module provides syntactic sugar for anonymous functions in type declarations and instantiation.

import std/[sequtils, sugar]

let powersOfTwo = @[1, 2, 4, 8, 16, 32, 64, 128, 256]

proc filter[T](s: openArray[T], pred: T -> bool): seq[T] =

result = newSeq[T]()

for i in 0 ..< s.len:

if pred(s[i]):

result.add(s[i])

echo powersOfTwo.filter(proc (x: int): bool = x > 32)

1. syntactic sugar for the above, provided as a macro from std/sugar

echo powersOfTwo.filter(x => x > 32)

proc greaterThan32(x: int): bool = x > 32

echo powersOfTwo.filter(greaterThan32)

Side effects of functions annotated with the noSideEffect pragma are checked, and the compiler will refuse to compile functions failing to meet those. Side effects in Nim include mutation, global state access or modification, asynchronous code, threaded code, and IO. Mutation of parameters may occur for functions taking parameters of var or ref type: this is expected to fail to compile with the currently-experimental strictFuncs in the future.{{Cite web |title=Nim Experimental Features: Strict Funcs |url=https://nim-lang.org/docs/manual_experimental.html#strict-funcs}} The func keyword introduces a shortcut for a noSideEffect pragma.{{Cite web |title=Nim Manual: Func |url=https://nim-lang.org/docs/manual.html#procedures-func}}

{{pre|1=

{{codett|lang=nim|func binarySearch[T](a: openArray[T]; elem: T): int}}

1. is short for...

{{codett|lang=nim|proc binarySearch[T](a: openArray[T]; elem: T): int}} {.noSideEffect.}

{.experimental: "strictFuncs".}

{{codett|lang=nim|type}}

{{codett|lang=nim|1=Node = ref object}}

{{codett|lang=nim|1=le, ri: Node}}

{{codett|lang=nim|1=data: string}}

{{codett|lang=nim|1=func len(n: Node): int =}}

# valid: len does not have side effects

{{codett|lang=nim|1=var it = n}}

{{codett|lang=nim|1=while it != nil:}}

{{codett|lang=nim|1=inc result}}

{{codett|lang=nim|1=it = it.ri}}

{{codett|lang=nim|1=func mut(n: Node) =}}

{{codett|lang=nim|1=let m = n # is the statement that connected the mutation to the parameter}}

{{codett|lang=nim|1=m.data = "yeah" # the mutation is here}}

{{codett|lang=nim|1=# Error: 'mut' can have side effects}}

{{codett|lang=nim|1=# an object reachable from 'n' is potentially mutated}}

}}

Uniform function call syntax allows the chaining of arbitrary functions, perhaps best exemplified with the std/sequtils library.{{Cite web |title=std/sequtils |url=https://nim-lang.org/docs/sequtils.html |access-date=2023-08-17 |website=nim-lang.org}}

import std/[sequtils, sugar]

let numbers = @[1, 2, 3, 4, 5, 6, 7, 8, 7, 6, 5, 4, 3, 2, 1]

1. a and b are special identifiers in the foldr macro

echo numbers.filter(x => x > 3).deduplicate.foldr(a + b) # 30

Nim has support for product types via the object type, and for sum types via object variants: raw representations of tagged unions, with an enumerated type tag that must be safely matched upon before fields of variants can be accessed.{{Cite web |title=Nim Manual: Object variants |url=https://nim-lang.org/docs/manual.html#types-object-variants |access-date=2023-08-17 |website=nim-lang.org}} These types can be composed algebraically. Structural pattern matching is available, but relegated to macros in various third-party libraries.{{Cite web |title=src/fusion/matching |url=https://nim-lang.github.io/fusion/src/fusion/matching.html |access-date=2023-08-17 |website=nim-lang.github.io}}

import std/tables

type

Value = uint64

Ident = string

ExprKind = enum

Literal, Variable, Abstraction, Application

Expr = ref object

case kind: ExprKind

of Literal:

litIdent: Value

of Variable:

varIdent: Ident

of Abstraction:

paramAbs: Ident

funcAbs: Expr

of Application:

funcApp, argApp: Expr

func eval(expr: Expr, context: var Table[Ident, Value]): Value =

case expr.kind

of Literal:

return expr.litIdent

of Variable:

return context[expr.varIdent]

of Application:

case expr.funcApp.kind

of Abstraction:

context[expr.funcApp.paramAbs] = expr.argApp.eval(context)

return expr.funcAbs.eval(context)

else:

raise newException(ValueError, "Invalid expression!")

else:

raise newException(ValueError, "Invalid expression!")

Despite being primarily an imperative and functional language, Nim supports various features for enabling object-oriented paradigms.{{Cite web |title=Nim Tutorial (Part II): Object Oriented Programming |url=https://nim-lang.org/docs/tut2.html#object-oriented-programming |access-date=2023-08-17 |website=nim-lang.org}}{{Cite web |title=Nim by Example - Object Oriented Programming |url=https://nim-by-example.github.io/oop/ |access-date=2023-08-17 |website=nim-by-example.github.io}}

Nim supports limited inheritance by use of ref objects and the of keyword. To enable inheritance, any initial ("root") object must inherit from RootObj. Inheritance is of limited use within idiomatic Nim code: with the notable exception of Exceptions.{{Cite web |title=system/exceptions |url=https://nim-lang.org/docs/exceptions.html |access-date=2023-08-17 |website=nim-lang.org}}

type Animal = ref object of RootObj

name: string

age: int

type Dog = ref object of Animal

type Cat = ref object of Animal

var animals: seq[Animal] = @[]

animals.add(Dog(name: "Sparky", age: 10))

animals.add(Cat(name: "Mitten", age: 10))

for a in animals:

assert a of Animal

Subtyping relations can also be queried with the of keyword.

Nim's uniform function call syntax enables calling ordinary functions with syntax similar to method call invocations in other programming languages. This is functional for "getters": and Nim also provides syntax for the creation of such "setters" as well. Objects may be made public on a per-field basis, providing for encapsulation.

type Socket* = ref object

host: int # private, lacks export marker

1. getter of host address

proc host*(s: Socket): int = s.host

1. setter of host address

proc `host=`*(s: var Socket, value: int) =

s.host = value

var s: Socket

new s

assert s.host == 0 # same as host(s), s.host()

s.host = 34 # same as `host=`(s, 34)

Static dispatch is preferred, more performant, and standard even among method-looking routines. Nonetheless, if dynamic dispatch is so desired, Nim provides the method keyword for enabling dynamic dispatch on reference types.

import std/strformat

type

Person = ref object of RootObj

name: string

Student = ref object of Person

Teacher = ref object of Person

method introduce(a: Person) =

raise newException(CatchableError, "Method without implementation override")

method introduce(a: Student) =

echo &"I am a student named {a.name}!"

method introduce(a: Teacher) =

echo &"I am a teacher named {a.name}!"

let people: seq[Person] = @[Teacher(name: "Alice"), Student(name: "Bob")]

for person in people:

person.introduce()

Nim supports simple substitution on the abstract syntax tree via its templates.

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.

Nim supports both constrained and unconstrained generic programming.

Generics may be used in procedures, templates and macros. Unconstrained generic identifiers (T in this example) are defined after the routine's name in square brackets. Constrained generics can be placed on generic identifiers, or directly on parameters.

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)

1. we don't want to risk subtracting unsigned numbers!

proc subtractThese[T: SomeSignedInt | float](a, b: T): T = a - b

echo subtractThese(1, 2) # -1 (of int type)

import std/sequtils

1. constrained generics can also be directly on the parameters

proc compareThese[T](a, b: string | seq[T]): bool =

for (i, j) in zip(a, b):

if i != j:

return false

One can further clarify which types the procedure will accept by specifying a type class (in the example above, SomeSignedInt).{{Cite web |title=Nim Manual: Type Classes |url=https://nim-lang.org/docs/manual.html#generics-type-classes |access-date=2020-07-21 |website=nim-lang.org}}

Macros can rewrite parts of the code at compile-time. Nim macros are powerful and can operate on the abstract syntax tree before or after semantic checking.{{Cite web |title=Nim Tutorial (Part III) |url=https://nim-lang.org/docs/tut3.html |access-date=2023-08-17 |website=nim-lang.org}}

Here's a simple example that creates a macro to call code twice:

import std/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 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!"

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.{{rp|226}}

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

proc printf(formatstr: cstring) {.header: "", 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 compiling 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.

{{Expand section|date=June 2019}}

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 std/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 std/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())

{{Expand section|date=June 2019}}

Asynchronous IO is supported either via the asyncdispatch module in the standard library or the external chronos library.{{Citation |title=Chronos - An efficient library for asynchronous programming |date=2023-08-14 |url=https://github.com/status-im/nim-chronos |access-date=2023-08-17 |publisher=Status}} Both libraries add async/await syntax via the macro system, without need for special language support. An example of an asynchronous HTTP server:

import std/[asynchttpserver, asyncdispatch]

1. chronos could also be alternatively used in place of asyncdispatch,
2. with no other changes.

var server = newAsyncHttpServer()

proc cb(req: Request) {.async.} =

await req.respond(Http200, "Hello World")

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

Nim has an active community on the self-hosted, self-developed official forum.{{cite web |url=http://forum.nim-lang.org |title=Nim Forum |publisher=nim-lang.org |access-date=2015-05-04}} Further, the project uses a Git repository, bug tracker, RFC tracker, and wiki hosted by GitHub, where the community engages with the language.{{cite web |url=https://github.com/Araq/Nim |title=Primary source code repository and bug tracker |website=GitHub |access-date=2015-05-04}} There are also official online chat rooms, bridged between IRC, Matrix, Discord, Gitter, and Telegram.{{Cite web |title=Community |url=https://nim-lang.org/community.html |access-date=2023-08-17 |website=Nim Programming Language |language=en}}

The first Nim conference, NimConf, took place on June 20, 2020. It was held digitally due to COVID-19, with an open call for contributor talks in the form of YouTube videos.{{cite web |url=https://nim-lang.org/blog/2020/05/14/nim-conference.html |title=Nim Online Conference 2020 |website=Nim |access-date=November 28, 2020}} The conference began with language overviews by Nim developers Andreas Rumpf and Dominik Picheta. Presentation topics included talks about web frameworks, mobile development, Internet of things (IoT) devices, and game development, including a talk about writing Nim for Game Boy Advance.{{cite web |title=NimConf 2020 |url=https://conf.nim-lang.org/2020/ |access-date=August 17, 2023 |website=Nim}} NimConf 2020 is available as a YouTube playlist.{{cite web |url=https://www.youtube.com/playlist?list=PLxLdEZg8DRwTIEzUpfaIcBqhsj09mLWHx |title=NimConf 2020 Playlist |website=YouTube |access-date=November 28, 2020}} NimConf 2021 occurred the following year, was also held digitally, and included talks about game development, REPLs, real-time operating systems, Nim in the industry, object-relational mapping (ORM), fuzzing, language design, and graphics libraries.{{Cite web |title=NimConf 2021 |url=https://conf.nim-lang.org/ |access-date=2023-08-17 |website=NimConf 2021 |language=en}}

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.{{cite web |url=http://www.oscon.com/open-source-2015/public/schedule/detail/42497 |title=Nim at OSCON 2015 |date=2015-07-20 |website=O'Reilly Open Source Convention (OSCON) |publisher=O'Reilly Media |access-date=2018-10-17 |archive-date=2015-10-06 |archive-url=https://web.archive.org/web/20151006182449/http://www.oscon.com/open-source-2015/public/schedule/detail/42497 |url-status=dead }}{{cite web |title=Essential Languages: Nim, Scala, Python |url=http://www.oreilly.com/pub/e/3420 |last1=Rumpf |first1=Andreas |last2=Swartz |first2=Jason |last3=Harrison |first3=Matt |website=O’Reilly |publisher=O'Reilly Media |access-date=2018-10-17}}{{cite AV media |last=Rumpf |first=Andreas |date=2015-10-26 |title=OSCON 2015 – Nim: An Overview |medium=Video |language=en |url=https://www.youtube.com/watch?v=4rJEBs_Nnaw |access-date=2018-10-12 |website=YouTube}} Four speakers represented Nim at FOSDEM 2020, including the creator of the language, Andreas Rumpf.{{Cite web|url=https://fosdem.org/2020/schedule/events/|title=Events|website=fosdem.org|language=en|access-date=2020-02-17}} At FOSDEM 2022, Nim hosted their own developer room virtually due to the COVID-19 pandemic.{{Cite web |title=Nim Devroom at FOSDEM 2022 - Call for Participation |url=https://nim-lang.org/blog/2021/12/02/fosdem-2022-cfp.html |access-date=2023-08-17 |website=Nim Programming Language |language=en}} Talks were held on concurrency, embedded programming, programming for GPUs, entity-component systems, game development, rules engines, Python interop, and metaprogramming.{{Cite web |title=Nim Programming Language devroom |url=https://archive.fosdem.org/2022/schedule/track/nim_programming_language/ |access-date=2023-08-17 |website=archive.fosdem.org |language=en}}

{{Portal|Computer programming}}

• Crystal (programming language)
• D (programming language)
• Fat pointer

{{Reflist|30em}}

• {{Official website}}
• {{GitHub|nim-lang/Nim}}
• [https://stackoverflow.com/questions/tagged/nim-lang Information about Nim] on Stack Overflow
• [http://ssalewski.de/nimprogramming.html Computer Programming with the Nim Programming Language] A gentle Introduction by Stefan Salewski

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