Skip to content

Severity: error
Category: type-check
Stage: Stage 1

Description

Two or more sum types in scope declare a variant with the same name (for example Ok on both Result<T, E> and another alias). When you construct that variant without an expected type context, the compiler cannot tell which sum type you mean and emits SJS-E020.

Add an explicit type annotation on the binding, parameter, or return position so the checker can resolve the intended sum type.

Example

type A = Ok(number) | Fail
type B = Ok(string) | Done

// ✗ error — Ok is ambiguous between A and B
const x = Ok(1)   // SJS-E020

Fix

Annotate the expected sum type (or narrow through a typed parameter / return type):

// ✓ correct — expected type disambiguates Ok
const x: A = Ok(1)

function toA(): A {
  return Ok(1)
}

Rename variants so they are unique module-wide when ambiguity is a recurring problem.

Related codes

  • SJS-E007 — non-exhaustive match expression
  • SJS-E002 — type mismatch
Documentation