import { U, Cons, Shareable } from '@stemcmicro/tree';
import { Sym, JsAtom } from '@stemcmicro/atoms';

type Sign = -1 | 0 | 1;
declare const SIGN_LT = -1;
declare const SIGN_EQ = 0;
declare const SIGN_GT = 1;
type CompareFn = (lhs: U, rhs: U) => Sign;

interface ExprHandler<T extends U> {
    binL(lhs: T, opr: Sym, rhs: U, env: ExprContext): U;
    binR(rhs: T, opr: Sym, lhs: U, env: ExprContext): U;
    dispatch(expr: T, opr: Sym, argList: Cons, env: ExprContext): U;
    /**
     * TODO: Migrate to using dispatch.
     */
    subst(expr: T, oldExpr: U, newExpr: U, env: Pick<ExprContext, "handlerFor">): U;
    /**
     * TODO: Migrate to using dispatch.
     */
    test(expr: T, opr: Sym, env: ExprContext): boolean;
}
interface ExprContext extends Shareable {
    clearBindings(): void;
    compareFn(opr: Sym): CompareFn;
    handlerFor<T extends U>(expr: T): ExprHandler<T>;
    hasBinding(opr: Sym, target: Cons): boolean;
    getBinding(opr: Sym, target: Cons): U;
    setBinding(opr: Sym, binding: U): void;
    hasUserFunction(name: Sym): boolean;
    getUserFunction(name: Sym): U;
    setUserFunction(name: Sym, usrfunc: U): void;
    defineUserSymbol(name: Sym): void;
    valueOf(expr: U): U;
    getDirective(directive: number): number;
    pushDirective(directive: number, value: number): void;
    popDirective(): void;
    getSymbolPrintName(sym: Sym): string;
    hasState(key: string): boolean;
    getState(key: string): Shareable;
    setState(key: string, value: Shareable): void;
}

/**
 * Here the first argument is the argument list and does not include the operator.
 */
type LambdaExpr = (argList: Cons, $: ExprContext) => U;

declare class Lambda extends JsAtom {
    #private;
    readonly type = "lambda";
    constructor(body: LambdaExpr, hash: string, pos?: number, end?: number);
    get hash(): string;
    get body(): LambdaExpr;
    equals(other: U): boolean;
    toString(): string;
}
declare function is_lambda(expr: U): expr is Lambda;

export { type CompareFn, type ExprContext, type ExprHandler, Lambda, type LambdaExpr, SIGN_EQ, SIGN_GT, SIGN_LT, type Sign, is_lambda };