tom-weatherhead/thaw-grammar

// tom-weatherhead/thaw-grammar/src/common/domain-object-model/cond-usage.ts

import { IEnvironmentFrame } from './environment-frame';
import { IExpression } from './iexpression';
import { IGlobalInfo } from './iglobal-info';

const typenameCondUsage = 'CondUsage';

export function isCondUsage<T>(obj: unknown): obj is CondUsage<T> {
    const condUsage = obj as CondUsage<T>;

    return typeof condUsage !== 'undefined' && condUsage.typename === typenameCondUsage;
}

export class CondUsage<T> implements IExpression<T> {
    public readonly typename: string = typenameCondUsage;

    constructor(public readonly exprPairList: [IExpression<T>, IExpression<T>][]) {}

    public toString(): string {
        return `(cond ${this.exprPairList
            .map(
                ([expr1, expr2]: [IExpression<T>, IExpression<T>]) =>
                    '(' + expr1.toString() + ' ' + expr2.toString() + ')'
            )
            .join(' ')})`;
    }

    public evaluate(
        globalInfo: IGlobalInfo<T>,
        localEnvironment?: IEnvironmentFrame<T>,
        options?: unknown
    ): T {
        for (const [expr1, expr2] of this.exprPairList) {
            if (!globalInfo.valueIsFalse(expr1.evaluate(globalInfo, localEnvironment, options))) {
                return expr2.evaluate(globalInfo, localEnvironment, options);
            }
        }

        return globalInfo.falseValue;
    }
}