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March 03, 2025 00:21
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Nim Programming Language Cheatsheet

A concise reference for the Nim programming language, covering syntax, data types, control flow, and advanced features for quick lookup and efficient coding.

Basic Syntax and Data Types

Fundamental Syntax

# - Single-line comment.
## - Multi-line comment.
; - Statement separator (usually optional).

Example:

# This is a single-line comment
## This is a
## multi-line comment
let x = 5; echo x # Statement separator used here

let - Immutable variable.
var - Mutable variable.
const - Compile-time constant.

Example:

let immutable = 10
var mutable = 20
mutable = 30 # OK
const compileTime = 40
# compileTime = 50 # Error: cannot assign to 'compileTime'

echo - Print to standard output.

Example:

echo "Hello, Nim!"
echo 1, 2, 3 # Prints: 1 2 3

Basic Data Types

int

Integer (platform-dependent size). Example: let x: int = 10

int8, int16, int32, int64

Signed integers of specific sizes. Example: let y: int32 = -1000

uint

Unsigned integer (platform-dependent size). Example: let z: uint = 100

uint8, uint16, uint32, uint64

Unsigned integers of specific sizes. Example: let a: uint16 = 65535

float, float32, float64

Floating-point numbers. Example: let b: float = 3.14

bool

Boolean (true or false). Example: let c: bool = true

char

Single character. Example: let d: char = 'A'

string

Sequence of characters. Example: let e: string = "Hello"

String Literals

"" - Regular string literal.
r"" - Raw string literal (no escape sequences).
"""" - Long string literal (can span multiple lines).

Example:

let normal = "Hello\nWorld"
let raw = r"Hello\nWorld"
let long = """
This is a
long string.
"""
echo normal # Prints: Hello\nWorld
echo raw    # Prints: Hello\\nWorld
echo long   # Prints: This is a\nlong string.

Control Flow and Procedures

Conditional Statements

if - Basic conditional statement.
elif - Else if.
else - Else.

Example:

let x = 10
if x > 0:
  echo "Positive"
elif x < 0:
  echo "Negative"
else:
  echo "Zero"

case - Switch statement.

Example:

let day = "Monday"
case day
of "Monday", "Tuesday", "Wednesday", "Thursday", "Friday":
  echo "Weekday"
of "Saturday", "Sunday":
  echo "Weekend"
else:
  echo "Invalid day"

Loops

for loop

Iterating over a range or collection.

for i in 0..5:
  echo i # Prints 0 to 5

let arr = [1, 2, 3]
for item in arr:
  echo item # Prints 1, 2, 3

while loop

Looping while a condition is true.

var i = 0
while i < 5:
  echo i
  i += 1

break statement

Exits the current loop.

for i in 0..10:
  if i > 5:
    break
  echo i # Prints 0 to 5

continue statement

Skips the current iteration and continues with the next.

for i in 0..5:
  if i mod 2 == 0:
    continue
  echo i # Prints 1, 3, 5

Procedures

proc - Define a procedure.

Syntax:

proc add(x, y: int): int =
  return x + y

let result = add(5, 3)
echo result # Prints 8

Parameters can have default values:

proc greet(name: string = "World") =
  echo "Hello, " & name

greet()       # Prints: Hello, World
greet("Nim")   # Prints: Hello, Nim

Discarding return values:

proc sayHello(): string =
  return "Hello"

discard sayHello()

Collections and Data Structures

Arrays and Sequences

array - Fixed-size collection.
seq - Dynamic array (sequence).

Example:

let arr: array[3, int] = [1, 2, 3]
var seq1: seq[int] = @[4, 5, 6] # @[] creates a sequence
seq1.add(7)
echo seq1 # Prints: @[4, 5, 6, 7]

Array access:

let value = arr[0] # Access the first element (index 0)
echo value       # Prints: 1

Sequence length:

echo seq1.len   # Prints: 4

Tuples and Objects

tuple

Collection of named fields with different types.

type Person = tuple[name: string, age: int]
let person1: Person = (name: "Alice", age: 30)
echo person1.name # Prints: Alice
echo person1.age  # Prints: 30

object

User-defined type with fields and methods (similar to classes in other languages).

type
  Rectangle = object
    width: float
    height: float

proc area(r: Rectangle): float =
  return r.width * r.height

var rect: Rectangle
rect.width = 5.0
rect.height = 3.0
echo area(rect) # Prints: 15.0

Sets and Dictionaries

set - Collection of unique elements.
Table - Hash table (dictionary).

Example:

import tables
import sets

var mySet: set[int] = {1, 2, 3}
mySet.incl(4)
echo mySet # Prints: {1, 2, 3, 4}

var myTable = initTable[string, int]()
myTable["Alice"] = 30
myTable["Bob"] = 25
echo myTable["Alice"] # Prints: 30

Advanced Features

Generics

Generic procedures and types allow you to write code that works with multiple types.

Example:

proc identity[T](x: T): T =
  return x

let intValue = identity[int](5)    # intValue is 5
let stringValue = identity[string]("Hello") # stringValue is "Hello"

echo intValue
echo stringValue

Metaprogramming

static

Evaluate code at compile time. Useful for generating code or performing calculations at compile time.

static:
  let compileTimeValue = 2 * 2
  echo "Compile time value: ", compileTimeValue # Prints during compilation

template

Code generation mechanism. Templates are expanded at compile time.

template twice(x: expr): expr =
  x * 2

let result = twice(5) # expands to 5 * 2
echo result        # Prints: 10

macro

More powerful than templates. Macros can manipulate the abstract syntax tree (AST) of the code.

import macros
macro assert(cond: expr, msg: string = "Assertion failed"):
  result = quote do:
    if not `cond`:
      raise newException(Defect, `msg`)

assert(1 == 1) # OK
# assert(1 == 2, "Custom message") # Raises an exception at runtime

Error Handling

try, except, finally - Exception handling.

Example:

try:
  let result = 10 div 0 # Raises an exception
  echo result
except DivByZeroError:
  echo "Division by zero error!"
finally:
  echo "This will always be executed."

raise - Raise an exception.

Example:

raise newException(ValueError, "Invalid value!")