Generics

Almide uses [] for generics, not <>. This eliminates ambiguity with comparison operators and makes parsing unambiguous for both compilers and LLMs.

Generic functions

Declare type parameters in [] after the function name:

fn identity[T](x: T) -> T = x

fn first[T](xs: List[T]) -> Option[T] = list.first(xs)

fn pair[A, B](a: A, b: B) -> (A, B) = (a, b)

Type arguments are inferred at the call site:

let n = identity(42)           // T = Int
let s = identity("hello")     // T = String
let p = pair(1, "one")        // A = Int, B = String

Generic types

Types can be parameterized:

type Pair[A, B] = {
  first: A,
  second: B,
}

type Tree[T] =
  | Leaf(T)
  | Node(Tree[T], Tree[T])

Use with concrete types:

let p: Pair[Int, String] = { first: 1, second: "one" }
let tree: Tree[Int] = Node(Leaf(1), Leaf(2))

Built-in generic types

The standard library uses generics extensively:

Type	Description
List[T]	Ordered homogeneous collection
Map[K, V]	Key-value collection
Set[T]	Unordered unique collection
Option[T]	Optional value (some(x) or none)
Result[T, E]	Success or failure (ok(x) or err(e))

Nested generics:

let data: Map[String, List[Int]] = ["scores": [90, 85, 92]]
let result: Result[List[String], String] = ok(["a", "b"])

Bounds

Type parameters can be constrained with protocol bounds using ::

fn show[T: Repr](item: T) -> String = item.repr()

fn process[T: Serializable](item: T) -> String = item.serialize()

Multiple bounds are joined with +:

fn show_named[T: Showable + Nameable](item: T) -> String =
  item.name() + ": " + item.show()

A comma inside the brackets separates type parameters, not bounds — [T: A, B] declares a second type parameter named B.

See Protocols for defining custom protocols that can be used as bounds.

Type application syntax

Almide always uses [] for type arguments:

List[Int]                        // list of integers
Map[String, List[Int]]           // nested generics
Result[User, ParseError]         // result type
Fn(Int, Int) -> Bool             // function type (no [] needed)

<> is never used for generics. < and > are always comparison operators.

Why [] instead of <>

Using [] for generics is a deliberate design choice:

• < and > are always comparison operators, never part of type syntax
• No ambiguity in expressions like a < b vs f<T>(x)
• Simpler parsing for both the compiler and LLMs generating code
• fn foo<T>(x: T) is rejected at parse time

Next steps

• Protocols — defining and implementing protocol bounds
• Types & Values — records, variants, and type aliases
• Functions — generic functions and type inference