import { FxError } from "@microsoft/teamsfx-api";
import { Result } from "neverthrow";
/** A value the evaluator yields. */
export type EvalValue = boolean | string;
/** The grammar's `null` literal and declared-but-unanswered marker. */
export declare const NULL_VALUE: unique symbol;
/** A resolved identifier's value: a string, or `NULL_VALUE` (unanswered / absent). */
export type ScopeValue = string | typeof NULL_VALUE;
/** Resolved identifier map; absent names are errors, not falsy defaults. */
export type Scope = Record<string, ScopeValue>;
/** Engine-owned, side-effect-free whitelist function. */
export type WhitelistFn = (...args: string[]) => string;
/** Pure evaluator port: whitelist functions plus read-only feature flags. */
export interface ExpressionRuntimePort {
    /** The fixed function whitelist; `undefined` for any non-whitelisted name. */
    functions(name: string): WhitelistFn | undefined;
    /** The feature-flag reader behind `featureFlag('…')` (env-backed, read-only). */
    flags(name: string): boolean;
}
/** Authored expression form, raw or sugar. */
export type ExpressionNode = {
    expr: string;
} | {
    equals: Record<string, string>;
} | {
    enum: Record<string, string[]>;
} | {
    anyOf: ExpressionNode[];
} | {
    featureFlag: string;
} | {
    capability: string;
} | {
    from: string;
};
/** `SystemError` names for expression evaluation failures. */
export declare const EXPR_UNDECLARED_IDENTIFIER = "ExprUndeclaredIdentifier";
export declare const EXPR_NON_WHITELISTED_FUNCTION = "ExprNonWhitelistedFunction";
export declare const EXPR_PARSE_ERROR = "ExprParseError";
/** Evaluate one authored expression against a resolved namespace. */
export declare function evaluateExpression(node: ExpressionNode, scope: Scope, port: ExpressionRuntimePort): Result<EvalValue, FxError>;
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