Curriculum Errors Error sets exercise 5 · fill-word
Error sets
Fill the missing prefix used at a RAISE site to refer to an
error variant. Same word as the type keyword. Read as
<prefix>.Empty — the prefix locates the variant in the
ambient error namespace.
TypeScript reference
Fill the blanks →
About this theme
An error set is a finite enumeration of named errors — declared as error{ Empty, BadDigit, ... }. Different APIs declare their own sets; the compiler tracks which errors a function can return as part of the type. error{} is the bottom set (no errors); the inferred set anyerror is the top (matches anything). A function returning ErrSet!T means: either T (success) or one of ErrSet's variants (failure). Composition is via the || operator — ErrA || ErrB makes a set covering both.