tom-weatherhead/thaw-grammar

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

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

const typenameIfUsage = 'IfUsage';

export function isIfUsage<T>(obj: unknown): obj is IfUsage<T> {
    const ifUsage = obj as IfUsage<T>;

    return typeof ifUsage !== 'undefined' && ifUsage.typename === typenameIfUsage;
}

export class IfUsage<T> implements IExpression<T> {
    public readonly typename: string = typenameIfUsage;

    constructor(
        public readonly condition: IExpression<T>,
        public readonly ifBody: IExpression<T>,
        public readonly elseBody: IExpression<T>
    ) {}

    public toString(): string {
        return `(if ${this.condition} ${this.ifBody} ${this.elseBody})`;
    }

    public evaluate(
        globalInfo: IGlobalInfo<T>,
        localEnvironment?: IEnvironmentFrame<T>,
        options?: unknown
    ): T {
        const conditionValue = this.condition.evaluate(globalInfo, localEnvironment, options);

        if (!globalInfo.valueIsFalse(conditionValue)) {
            return this.ifBody.evaluate(globalInfo, localEnvironment, options);
        } else {
            return this.elseBody.evaluate(globalInfo, localEnvironment, options);
        }
    }
}