tom-weatherhead/thaw-grammar

// tom-weatherhead/thaw-grammar/src/languages/prolog/domain-object-model/interfaces/ivariable.ts

import { IImmutableSet } from 'thaw-common-utilities.ts';

import { IPrologExpression } from './iprolog-expression';

import { IPrologNumber } from './iprolog-number';

import { ISubstitution } from './isubstitution';

export const typenamePrologVariable = 'PrologVariable';

export interface IPrologVariable extends IPrologExpression {
    // readonly typename: string;
    readonly Name: string;

    IsNonBinding: boolean;
    IsGround: boolean;

    FindBindingVariables(): IImmutableSet<IPrologVariable>; // or IImmutableSet<string>?
    GetListOfBindingVariables(): IPrologVariable[]; // or IImmutableArray<string>?
    ContainsVariable(v: IPrologVariable): boolean;
    ApplySubstitution(sub: ISubstitution): IPrologExpression;
    Unify(otherExpr: IPrologExpression): ISubstitution | undefined;
    EvaluateToNumber(): IPrologNumber | undefined;
}

export function isIPrologVariable(obj: unknown): obj is IPrologVariable {
    const otherIVariable = obj as IPrologVariable;

    return (
        typeof otherIVariable !== 'undefined' &&
        otherIVariable.typename === typenamePrologVariable &&
        typeof otherIVariable.Name === 'string'
    );
}