tom-weatherhead/thaw-grammar

// tom-weatherhead/thaw-grammar/src/languages/lisp/domain-object-model/sexpression-list.ts

import { ISExpression } from './isexpression';
import { NullSExpression } from './null-sexpression';
import { SExpressionBase } from './sexpression-base';

const typenameSExpressionList = 'SExpressionList';

export function isSExpressionList(obj: unknown): obj is SExpressionList {
    const sexlist = obj as SExpressionList;

    return typeof sexlist !== 'undefined' && sexlist.typename === typenameSExpressionList;
}

export class SExpressionList extends SExpressionBase {
    public static makeFromList(l: ISExpression[]): ISExpression {
        return this.makeFromListHelper(l, 0);
    }

    private static makeFromListHelper(l: ISExpression[], i: number): ISExpression {
        if (i >= l.length) {
            return new NullSExpression();
        }

        return new SExpressionList(l[i], this.makeFromListHelper(l, i + 1));
    }

    public readonly typename: string = typenameSExpressionList;

    // These two data members cannot be readonly, because of thunk evaluation.
    public head: ISExpression;
    public tail: ISExpression;

    constructor(head: ISExpression, tail: ISExpression) {
        super();

        this.head = head;
        this.tail = tail;
    }

    public toString(): string {
        // return `(${this.ToStringWithoutBrackets()})`;

        return '(' + this.toStringWithoutBrackets() + ')';
    }

    public override isList(): boolean {
        return true;
    }

    public getLength(): number {
        const tail = this.tail as SExpressionList;

        return tail === undefined ? 1 : tail.getLength() + 1;
    }

    private toStringWithoutBrackets(): string {
        if (this.tail.isNull()) {
            return this.head.toString();
        } else if (isSExpressionList(this.tail)) {
            return `${this.head} ${this.tail.toStringWithoutBrackets()}`;
        } else {
            // tail is a symbol, an integer literal, a string, a closure, etc.
            return `${this.head} . ${this.tail.toString()}`;
        }
    }

    public override isEqualTo(other: unknown): boolean {
        return (
            isSExpressionList(other) &&
            this.head.isEqualTo(other.head) &&
            this.tail.isEqualTo(other.tail)
        );
    }
}