How to use tau-prolog - 6 common examples

import {Project}      from '@yarnpkg/core';
import {PortablePath} from '@yarnpkg/fslib';
import getPath        from 'lodash/get';
import pl             from 'tau-prolog';

// eslint-disable-next-line @typescript-eslint/camelcase
const {is_atom: isAtom} = pl.type;

function prependGoals(thread: pl.type.Thread, point: pl.type.State, goals: pl.type.Term[]): void {
  thread.prepend(goals.map(
    goal => new pl.type.State(
      point.goal.replace(goal),
      point.substitution,
      point,
    ),
  ));
}

const projects = new WeakMap();

function getProject(thread: pl.type.Thread): Project {
  const project = projects.get(thread.session);

[`workspace_field/3`]: (thread, point, atom) => {
    const [workspaceCwd, fieldName, fieldValue] = atom.args;

    if (!isAtom(workspaceCwd) || !isAtom(fieldName)) {
      thread.throwError(pl.error.instantiation(atom.indicator));
      return;
    }

    const project = getProject(thread);
    const workspace = project.tryWorkspaceByCwd(workspaceCwd.id as PortablePath);

    // Workspace not found => this predicate can never match
    // We might want to throw here? We can be pretty sure the user did
    // something wrong at this point
    if (workspace == null)
      return;

    const value = getPath(workspace.manifest.raw!, fieldName.id);

    // Field is not present => this predicate can never match
    if (typeof value === `undefined`)

function extractErrorImpl(value: any): any {
  if (value instanceof pl.type.Num)
    return value.value;

  if (value instanceof pl.type.Term) {
    if (value.args.length === 0)
      return value.id;

    switch (value.indicator) {
      case `throw/1`:
        return extractErrorImpl(value.args[0]);
      case `error/1`:
        return extractErrorImpl(value.args[0]);
      case `error/2`:
        return Object.assign(extractErrorImpl(value.args[0]), ...extractErrorImpl(value.args[1]));
      case `syntax_error/1`:
        return new ReportError(MessageName.PROLOG_SYNTAX_ERROR, `Syntax error: ${extractErrorImpl(value.args[0])}`);
      case `existence_error/2`:
        return new ReportError(MessageName.PROLOG_EXISTENCE_ERROR, `Existence error: ${extractErrorImpl(value.args[0])} ${extractErrorImpl(value.args[1])} not found`);
      case `line/1`:
        return {line: extractErrorImpl(value.args[0])};

function extractErrorImpl(value: any): any {
  if (value instanceof pl.type.Num)
    return value.value;

  if (value instanceof pl.type.Term) {
    if (value.args.length === 0)
      return value.id;

    switch (value.indicator) {
      case `throw/1`:
        return extractErrorImpl(value.args[0]);
      case `error/1`:
        return extractErrorImpl(value.args[0]);
      case `error/2`:
        return Object.assign(extractErrorImpl(value.args[0]), ...extractErrorImpl(value.args[1]));
      case `syntax_error/1`:
        return new ReportError(MessageName.PROLOG_SYNTAX_ERROR, `Syntax error: ${extractErrorImpl(value.args[0])}`);
      case `existence_error/2`:

    goal => new pl.type.State(
      point.goal.replace(goal),
      point.substitution,
      point,
    ),
  ));

public constructor(project: Project, source: string) {
    this.session = pl.create();
    linkProjectToSession(this.session, project);

    this.session.consult(source);
  }