type-inference gradual-typing elixir set-theoretic-types verified-bugs

Elixir v1.20 infers types without annotations

Elixir's gradual type system now performs inference across existing code via the dynamic() type, catching verified bugs (type violations guaranteed to fail at runtime) with near-zero false positives—no annotations required.

June 4, 2026

Summary

Developers get dead code detection and runtime bug verification in existing Elixir programs without overhead or trust erosion from false positives. Type narrowing from guards and pattern matching refines dynamic() constraints as code executes, catching real errors early.

Why it matters

Implementation verdict

Replaces manual type annotation burden for the first milestone; requires Elixir v1.20+. Ready now for detection workflows, but annotation-free inference is the shipped feature. When user annotations land, static typing becomes opt-in. No migration cost—runs alongside existing code.

Sources

1.perform type inference and gradually type check every Elixir program, without introducing type annotations
2.typing violations that are guaranteed to fail at runtime if executed
3.Elixir can find verified bugs in existing programs efficiently, without introducing developer overhead, and with an extremely low false positives rate
4.Elixir passes 12 of the 13 categories, showing that it can recover precise type information from ordinary Elixir code, which we use to find verified bugs in dynamically typed programs
5.the dynamic() type in Elixir effectively works as a range, which can be refined as it is used throughout the program and reports violations whenever type checks fall outside of the range

Dev Signal

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