Karthik Divi
·4 min read

Nim Online Compiler - Run Nim Code in Your Browser

onecompileronline-compilerprogrammingnim

Nim looks like Python but compiles to C. That sentence alone is enough to make systems programmers do a double-take.

The syntax uses significant whitespace and reads almost like pseudocode. But instead of running through an interpreter, Nim's compiler translates your code to C (or C++, or JavaScript, or even Objective-C), then compiles that with your system's C compiler. The result is a native binary with performance comparable to hand-written C, produced from code that took a fraction of the time to write.

Installing Nim locally involves choosenim (its version manager) or building from source. Neither is complicated, but if you want to test a procedure or see how Nim's type inference works, firing up a Nim online compiler is faster.

Python-like, but the compiler has your back

Nim's type inference means you rarely write type annotations for local variables, but the compiler still knows the type of everything. And Nim's metaprogramming system -- templates and macros -- lets you generate code at compile time without sacrificing readability.

import std/[strformat, sequtils, sugar, tables]

type
  Student = object
    name: string
    grades: seq[int]

proc average(grades: seq[int]): float =
  if grades.len == 0: return 0.0
  grades.foldl(a + b, 0) / grades.len

proc status(avg: float): string =
  if avg >= 90: "excellent"
  elif avg >= 70: "good"
  elif avg >= 50: "passing"
  else: "needs improvement"

let students = @[
  Student(name: "Alice", grades: @[92, 88, 95, 91]),
  Student(name: "Bob", grades: @[78, 65, 82, 70]),
  Student(name: "Carol", grades: @[45, 52, 48, 55]),
]

for s in students:
  let avg = s.grades.average()
  echo fmt"{s.name}: avg={avg:.1f} ({status(avg)})"

# Nim compiles to C -- check the performance yourself
echo "\nGrade distribution:"
let allGrades = students.mapIt(it.grades).foldl(a & b)
let distribution = allGrades.countIt(it >= 90)
echo fmt"  A grades (>=90): {distribution} out of {allGrades.len}"

A few things to notice. The proc average has no explicit return type annotation on the parameter grades -- but Nim infers it from the call site. The foldl and mapIt calls use Nim's template system, not runtime closures. And fmt is a compile-time string formatter that produces zero-overhead formatting code.

The whole thing reads like a scripting language but produces a compiled binary.

Multiple backends, one language

This is where Nim gets genuinely interesting. The same Nim code can compile to:

  • C -- for native performance and easy FFI with existing C libraries
  • C++ -- when you need to interface with C++ codebases
  • JavaScript -- for browser and Node.js targets
  • Objective-C -- for iOS development

One language, multiple deployment targets. Write your business logic in Nim, compile to JavaScript for the frontend and C for the backend. It's not theoretical -- people actually do this.

Nim's metaprogramming goes deep too. Templates give you hygienic code generation. Macros give you access to the AST at compile time. You can write DSLs, generate boilerplate, and specialize code paths without preprocessor hacks.

An online compiler is handy for:

  • Checking how Nim syntax differs from Python when you're switching between the two
  • Testing template and macro behavior without setting up a local project
  • Sharing Nim examples with developers who haven't installed it yet
  • Quickly verifying that a procedure works before integrating it into a larger project

Run Nim on OneCompiler

OneCompiler's Nim online compiler compiles and runs your Nim code in the browser. Write a procedure, test your logic, share the link. No choosenim, no build step, no waiting.

If you write Python and wish it were faster, or you write C and wish it were less painful, Nim is worth 10 minutes of your time. Start with the compiler that's already running.