Free-function overloading is implemented but the Language Spec does not describe it

GAP-FUNCTIONS-001

A module can declare several free functions with one name and the compiler resolves calls by exact argument types, but the spec states no rules for it, including whether an overloaded name can be used as a value.

Lifecycle

known

Owner

language

Scope

reference/spec/functions.md#first-class-functions

Origin

answering whether same-named functions share a SymbolId; checked against reference/spec/functions.md

Affects · linked records

spec.functions.first-class-functions.legality-2language spec rule

RFC-0128rfc

LIMIT-TYPE-CONSTRUCTION-002limitation

gapKnown gaps ↗

Gap

The compiler supports free-function overloading (METEL-180): a module may declare several funs with one name if they are non-generic, fully annotated and differ in their parameter types (identical signatures are T0011); a call selects a definition by exact argument types, with no implicit numeric coercion. None of this is in the Language Spec. The only mention of overloading in reference/spec/ is the built-in assert (runtime.md). The spec has no rule for declaring overloads, for how a call picks one, for what makes two definitions distinct, or for the restrictions (non-generic, module-local: an overload set is not exported across modules, LIMIT-TYPE-CONSTRUCTION-002).

One consequence is visibly undefined. An overloaded name cannot be used as a value: let g := f; and apply(f) both fail with T0003 undefined name f`` (metel-core#1230). Whether that is intended, or whether f should resolve against an expected function type, is a language decision the spec does not make.

Impact

Programmers can use a feature the spec never promises, and cannot tell from it what is guaranteed, what is an accident of the current implementation, or how overloads interact with function values, generics and imports. Method overloading is also unspecified; the implementation does not support it (metel-core#1229).

Affects

• spec.functions.first-class-functions.legality-2
• RFC-0128
• LIMIT-TYPE-CONSTRUCTION-002

Resolution

None yet. RFC-0128 (draft) covers exportable overload sets; specifying the rules above, including overloaded function values, needs its own accepted design.