dotlr/src/utils.ts

An LR(1) parser generator and visualizer created for educational purposes.

import type {
  Action,
  AtomicPattern,
  GrammarError,
  Item,
  ParserError,
  ParsingError,
  Rule,
  Token,
  Tree,
} from "./types";

export function stringifyToken(token: Token, noApostrophes = false) {
  if (token.type === "Eof") return "$";
  if (token.type === "Empty") return "ε";
  if (token.type === "Regex") return `%${token.value}`;
  if (token.type === "Constant")
    return noApostrophes ? token.value : `'${token.value}'`;
  return "";
}

export function stringifyAtom(atom: AtomicPattern, noApostrophes = false) {
  if (atom.type === "Symbol") return atom.value;
  if (atom.type === "Token") return stringifyToken(atom.value, noApostrophes);
  return "";
}

export function stringifyItem(item: Item, noApostrophes = false) {
  const children = item.rule.pattern.map((a) =>
    stringifyAtom(a, noApostrophes),
  );
  //inserts the dot
  children.splice(item.dot, 0, ".");
  return `${item.rule.symbol} -> ${children.join(" ")}`;
}

export function stringifyRule(rule: Rule, noApostrophes = false) {
  const children = rule.pattern.map((a) => stringifyAtom(a, noApostrophes));
  return `${rule.symbol} -> ${children.join(" ")}`;
}

export function stringifyLookahead(item: Token[], noApostrophes = false) {
  const children = item.map((t) => stringifyToken(t, noApostrophes));
  return children.join(" ");
}

export function stringifyAction(action: Action) {
  if (action.type === "Accept") return `a${action.value.rule_index + 1}`;
  if (action.type === "Reduce") return `r${action.value.rule_index + 1}`;
  if (action.type === "Shift") return `s${action.value.next_state}`;
  return "";
}

export function stringifyActionVerbose(
  action: Action,
  rules: Rule[],
  noApostrophes: boolean = false,
) {
  if (action.type === "Shift") {
    return `Shift ${action.value.next_state}`;
  } else if (action.type === "Accept") {
    return `Accept ${action.value.rule_index + 1} (${stringifyRule(rules[action.value.rule_index], noApostrophes)})`;
  } else if (action.type === "Reduce") {
    return `Reduce ${action.value.rule_index + 1} (${stringifyRule(rules[action.value.rule_index], noApostrophes)})`;
  }
  return "";
}

export function stringifyTreeStack(
  tree: Tree[],
  noApostrophes = false,
): string[] {
  return tree.map((i) => {
    if (i.type === "Terminal")
      return stringifyToken(i.value.token, noApostrophes);
    if (i.type === "NonTerminal") return i.value.symbol;
  });
}

export function stringifyTree(
  tree: Tree,
  indent: string = "",
  isLast: boolean = true,
): string {
  const linePrefix = isLast ? "└─ " : "├─ ";
  let result = "";

  if (tree.type === "Terminal") {
    const { token, slice } = tree.value;
    if (token.type !== "Eof" && token.type !== "Empty") {
      result += `${indent}${linePrefix}${token.value} [${slice}]\n`;
    }
  } else {
    const { symbol, pattern } = tree.value;
    result += `${indent}${linePrefix}${symbol}\n`;

    const newIndent = indent + (isLast ? "   " : "│  ");
    pattern.forEach((child, index) => {
      result += stringifyTree(child, newIndent, index === pattern.length - 1);
    });
  }

  return result;
}

export function stringifyGrammarError(e: GrammarError) {
  if (e.type === "UnexpectedToken") {
    return `Unexpected token at ${stringifySpan(e.value)}, expected one of:\n${e.value.expected.map(maybeToken).join(", ")}`;
  } else if (e.type === "UnexpectedEof") {
    return `Unexpected end of input, expected one of:\n${e.value.expected.map(maybeToken).join(", ")}`;
  } else if (e.type === "InvalidRegex") {
    return `Invalid regular expression at ${stringifySpan(e.value)}\n${e.value.regex}`;
  }
  return "Unknown error";
}

function maybeToken(token: Token | string) {
  return typeof token === "string" ? token : stringifyToken(token);
}

function stringifySpan(span: { column: number; line: number }) {
  return `${span.line}:${span.column}`;
}

export function stringifyParsingError(error: ParsingError) {
  if (error.type === "UnexpectedEof") {
    return `Unexpected end of input at ${stringifySpan(error.value.span)}, expected one of:\n${error.value.expected.map(maybeToken).join(", ")}`;
  } else if (error.type === "UnknownToken") {
    return `Unknown token at ${stringifySpan(error.value.span)}: ${error.value.token}`;
  } else if (error.type === "UnexpectedToken") {
    return `Unexpected token at ${stringifySpan(error.value.span)}, expected one of:\n${error.value.expected.map(maybeToken).join(", ")}`;
  }
  return "Unknown error";
}

export function stringifyParserError(error: ParserError) {
  if (error.type === "EmptyGrammar") return "Empty grammar";
  if (error.type === "UndefinedSymbol")
    return `Undefined symbol: ${error.value.symbol}`;
  if (error.type === "UndefinedRegexToken")
    return `Undefined regex token: ${error.value.regex_token}`;
  if (error.type === "Conflict")
    return `Conflict in state ${error.value.state} on token ${stringifyToken(error.value.token)}`;
  return "Unknown error";
}

export function stringifyError(
  error: GrammarError | ParsingError | ParserError,
) {
  const s = stringifyGrammarError(error as GrammarError);
  const s2 = stringifyParsingError(error as ParsingError);
  const s3 = stringifyParserError(error as ParserError);
  if ([s, s2, s3].every((s) => s === "Unknown error")) return "Unknown error";
  if (s !== "Unknown error") return s;
  if (s2 !== "Unknown error") return s2;
  return s3;
}