Nullability and Type Checking

Kelvra is strictly typed by default. The repo has broad type-error coverage, and the docs should reflect that posture instead of softening it.

Nullable types

Nullable types are written with ?.

var maybeScore i32? = 7
if (maybeScore != null) {
  print("score present")
}

You can also assign null later:

type Dog struct {
  fn bark() str {
    return "woof"
  }
}

var maybeDog Dog? = Dog()
maybeDog = null

Explicit null checks

The current type checker expects explicit checks before optional member access or optional calls. The repo includes negative tests for both.

if (maybeDog != null) {
  print("dog present")
}

Assignment rules

The type checker already rejects:

• assigning null to non-optional bindings
• assigning the wrong primitive or collection type
• assigning to const
• invalid subtype assignments
• invalid handle/package-type mixing

Function checking

Functions are checked for:

• argument type mismatches
• lambda parameter and return mismatches
• invalid casts
• wrong return types
• missing values on non-void returns

Control-flow checking

The repo also enforces loop-control correctness:

• break outside loops is rejected
• continue outside loops is rejected
• unknown loop labels are rejected
• duplicate loop labels are rejected

Imports and types

Typed imports are checked too. Existing tests cover:

• missing imported symbols
• typed import binding mismatches
• native package binding mismatches
• import cycles surfaced during frontend analysis

Related pages

• Values and Bindings
• Modules and Imports
• Syntax Rules