The spec defines future array operations map, fold, and slice as built-in functions (Chapter 4, Section 4.7).

These depend on #60 (abilities and type constraints) to express the type constraints on the mapping/folding functions. Without abilities, the higher-order function arguments cannot be properly typed.

Spec reference: Chapter 4 (Expressions), Section 4.7 — "Future array operations (map, fold, slice) will be added alongside the module system and abilities."