/**
 * Function Registry — Declarative function descriptors and native implementations.
 *
 * Each function is described by a `FunctionDescriptor` that carries metadata
 * about arity and the implementation itself. The evaluator uses this metadata
 * to validate arguments and invoke functions.
 *
 * Special forms (IF, LET, LAMBDA, etc.) are NOT registered here — they
 * are handled directly by the evaluator's special-form dispatch.
 */
import type { RuntimeValue } from "./values.js";
/**
 * A function descriptor with metadata and implementation.
 */
export interface FunctionDescriptor {
    /** Canonical uppercase name. */
    readonly name: string;
    /** Minimum number of arguments. */
    readonly minArity: number;
    /** Maximum number of arguments. Infinity for variadic. */
    readonly maxArity: number;
    /**
     * The function implementation.
     * Receives eagerly evaluated arguments as `RuntimeValue[]`.
     * Returns a `RuntimeValue`.
     */
    readonly invoke: (args: RuntimeValue[]) => RuntimeValue;
}
/**
 * Register a function descriptor. The descriptor is stored under its
 * canonical (unprefixed) name only — `_XLFN.` / `_XLFN._XLWS.` prefix
 * variants are resolved dynamically in `lookupFunction`. This keeps the
 * registry small and avoids triple-entry bookkeeping for 200+ functions.
 */
export declare function registerFunction(desc: FunctionDescriptor): void;
/**
 * Look up a function by uppercase name. Accepts `_XLFN.` and
 * `_XLFN._XLWS.` prefixed variants by stripping the prefix before lookup
 * (a no-op for plain names, so plain lookups also go through a single
 * Map.get call — avoiding the double-lookup pattern used previously).
 *
 * Fast-path: the overwhelming majority of lookups use plain names
 * (`SUM`, `IF`, `VLOOKUP`, …). Checking the prefix sentinel byte up
 * front lets those callers skip the `slice`/`startsWith` machinery in
 * `stripFunctionPrefix` entirely.
 */
export declare function lookupFunction(name: string): FunctionDescriptor | undefined;
/**
 * Convenience: define and register an eager function.
 */
export declare function defineEager(name: string, minArity: number, maxArity: number, invoke: (args: RuntimeValue[]) => RuntimeValue): FunctionDescriptor;
export declare function ensureRegistryInitialized(): void;