Module function_catalog 

Function catalog — static table of built-in scalar / aggregate function signatures used by the Fase 3 expression typer to resolve Expr::FunctionCall nodes to a concrete return type.

Mirrors PostgreSQL’s pg_proc catalog with a deliberately narrow row shape: a single (name, arg_types, return_type, kind) entry per overload. Multiple entries may share the same name — the resolver picks the one whose argument types match (after implicit coercion) using the func_select_candidate heuristic described in the roadmap (parte 4 of the plan file).

The table is const &[FunctionEntry] so it lives in the read-only segment and lookups stay cache-friendly. Linear scan is fine for the ~30 entries the catalog covers today. Future weeks can switch to a HashMap<&'static str, &[…]> grouped by name when the table grows past ~500 entries.

Coverage today

Aggregates: COUNT, SUM, AVG, MIN, MAX (the five SQL-standard ones). Each has multiple overloads for the numeric category.

Scalars covered:

• String: UPPER, LOWER, LENGTH, COALESCE
• Math: ABS, ROUND, FLOOR, CEIL
• Time: NOW, CURRENT_TIMESTAMP, CURRENT_DATE, TIME_BUCKET
• Geo: GEO_DISTANCE, GEO_BEARING, HAVERSINE
• Misc: VERIFY_PASSWORD

Variadic functions (COALESCE, GREATEST, LEAST, CONCAT) are marked with variadic: true and the resolver treats their arg_types slice as a description of the uniform element type — the catalog can’t enumerate every arity, so the typer checks each call-site argument against arg_types[0] instead.

What’s NOT in this catalog

• User-defined functions (CREATE FUNCTION) — separate runtime table, queried after the static catalog yields no match.
• Polymorphic signatures (anyelement, anyarray) — Fase 3 W4.
• Operator functions backing +, -, * — those go in pg_operator equivalent which we haven’t built yet.

Structs

FunctionEntry

One signature in the static function catalog.

Enums

FunctionKind

Function classification — affects resolver behavior and downstream planner cost estimation.

Constants

FUNCTION_CATALOG

The static function catalog. Append-only; removing a row is a breaking change that may invalidate cached plans referencing the function. Each block is grouped by category for readability.

Functions

lookup

Look up a function by name, returning the slice of overloads (possibly empty). The resolver walks this slice and picks the best match using its own coercion logic.

resolve

Resolve a function call to the best-matching overload. Returns None when no overload matches the call-site argument types (after implicit coercion).