The Absurdity of Error Handling: Finding a Purpose for Errors in Safety-Critical SYCL Erik Tomusk CppCon 2023 October 5, 2023© 2023 Codeplay Software Ltd. Codeplay Corporate Slide 2© 2023 Codeplay are so well-defined, predictable, and well-understood as to allow application-level recovery • Absurdity of error handling: The set of errors that can be “handled” is (nearly) empty • Is error handling

compatible with --safe. Absurd clauses do not need any special handling (since the transport of an absurdity is still absurd), so definitions which rely on Agda’s ability to automatically separate constructors This implies all applications of absurd are the same: only-one-absurdity : {A : Set} → (p q : ⊥) → absurd A p ≡ absurd A q only-one-absurdity p q = refl Since pattern matching on datatypes in Prop is limited

compatible with --safe. Absurd clauses do not need any special handling (since the transport of an absurdity is still absurd), so defini- tions which rely on Agda’s ability to automatically separate constructors same: 3.32. Prop 145 Agda User Manual, Release 2.6.3 only-one-absurdity : {A : Set} → (p q : ⊥) → absurd A p ≡ absurd A q only-one-absurdity p q = refl Since pattern matching on datatypes in Prop is limited

compatible with --safe. Absurd clauses do not need any special handling (since the transport of an absurdity is still absurd), so defini- tions which rely on Agda’s ability to automatically separate constructors This implies all applications of absurd are the same: only-one-absurdity : {A : Set} → (p q : ⊥) → absurd A p ≡ absurd A q only-one-absurdity p q = refl Since pattern matching on datatypes in Prop is limited

compatible with --safe. Absurd clauses do not need any special handling (since the transport of an absurdity is still absurd), so defini- tions which rely on Agda’s ability to automatically separate constructors This implies all applications of absurd are the same: only-one-absurdity : {A : Set} → (p q : ⊥) → absurd A p ≡ absurd A q only-one-absurdity p q = refl Since pattern matching on datatypes in Prop is limited

compatible with --safe. Absurd clauses do not need any special handling (since the transport of an absurdity is still absurd), so defini- tions which rely on Agda’s ability to automatically separate constructors This implies all applications of absurd are the same: only-one-absurdity : {A : Set} → (p q : ⊥) → absurd A p ≡ absurd A q only-one-absurdity p q = refl Since pattern matching on datatypes in Prop is limited

compatible with --safe. Absurd clauses do not need any special handling (since the transport of an absurdity is still absurd), so defini- tions which rely on Agda’s ability to automatically separate constructors This implies all applications of absurd are the same: only-one-absurdity : {A : Set} → (p q : ⊥) → absurd A p ≡ absurd A q only-one-absurdity p q = refl Since pattern matching on datatypes in Prop is limited

This implies all applications of absurd are the same: only-one-absurdity : {A : Set} → (p q : ⊥) → absurd A p ≡ absurd A q only-one-absurdity p q = refl Since pattern matching on datatypes in Prop is limited

This implies all applications of absurd are the same: only-one-absurdity : {A : Set} → (p q : ⊥) → absurd A p ≡ absurd A q only-one-absurdity p q = refl Since pattern matching on datatypes in Prop is limited

This implies all applications of absurd are the same: only-one-absurdity : {A : Set} → (p q : ⊥) → absurd A p ≡ absurd A q only-one-absurdity p q = refl Since pattern matching on datatypes in Prop is limited