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recursive-descent-parser.ts
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recursive-descent-parser.ts
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import {
createEventEmitter,
EventEmitter,
} from "../runtime/async/event-emitter.ts";
export interface RecursiveDescentParser<
T extends Record<string, any> = any,
> extends EventEmitter<T> {
readonly input: string;
loc: number;
offsetToColRow: (offset: number) => ColRow;
colRowToOffset: (colRow: ColRow) => number;
getAroundText: (loc: number, length?: number, window?: number) => string;
try(pattern: Pattern): Token | undefined;
accept(pattern: Pattern): Token | undefined;
expect(
acceptPattern: Pattern,
expectedPatterns?: Pattern[],
mistakePatterns?: Pattern[],
): Token;
}
export interface RecursiveDescentParserConfig {
debug: boolean;
}
export interface Span {
start: number;
end: number;
}
export interface ColRow {
col: number;
row: number;
}
export interface Token extends Span {
text: string;
}
export type Pattern = string | RegExp | typeof eof;
export const eof = Symbol("<EOF>");
export function createRecursiveDescentParser<
T extends Record<string, any> = any,
>(
input: string,
config?: Partial<RecursiveDescentParserConfig>,
): RecursiveDescentParser<T> {
const debug = !!config?.debug;
let cnt = 0;
const lines = input.split("\n");
const parser: RecursiveDescentParser<T> = {
...createEventEmitter<T>(),
input,
loc: 0,
offsetToColRow: (offset) => offsetToColRow(lines, offset),
colRowToOffset: (colRow) => colRowToOffset(lines, colRow),
getAroundText: (loc, length, window) =>
getAroundText(
lines,
loc,
length,
window,
),
try(pattern) {
const loc = parser.loc;
try {
return parser.accept(pattern);
} finally {
parser.loc = loc;
}
},
accept(pattern) {
cnt++;
if (cnt > input.length * 5) throw `infinite loop`;
if (pattern === eof) return acceptEof();
if (typeof pattern === "string") return acceptString(pattern);
return acceptRegex(pattern);
},
expect(acceptPattern, expectedPatterns, mistakePatterns) {
const result = parser.accept(acceptPattern);
const _expectedPatterns: Pattern[] = (
expectedPatterns
? [acceptPattern, ...expectedPatterns]
: [acceptPattern]
);
if (result == null) {
throw new SyntaxError(parser, _expectedPatterns, mistakePatterns);
} else {
return result;
}
},
};
function acceptEof(): Token | undefined {
if (parser.loc < input.length) return;
return { start: parser.loc, end: parser.loc, text: "" };
}
function acceptString(pattern: string): Token | undefined {
const start = parser.loc;
const end = start + pattern.length;
const text = input.slice(start, end);
if (text !== pattern) return;
parser.loc = end;
debug && console.log(text);
return { start, end, text };
}
function acceptRegex(pattern: RegExp): Token | undefined {
pattern.lastIndex = 0;
const execArray = pattern.exec(input.substr(parser.loc));
if (execArray == null) return;
const text = execArray[0];
const start = parser.loc + execArray.index;
const end = start + text.length;
parser.loc = end;
debug && console.log(text);
return { start, end, text };
}
return parser;
}
export class SyntaxError extends Error {
constructor(
public parser: RecursiveDescentParser,
public expectedPatterns: Pattern[],
public mistakePatterns: Pattern[] = [],
) {
super();
const colRow = this.colRow;
const got = this.got;
const length = got === eof ? 1 : got.length;
const expectedPatternsText = expectedPatterns.map(patternToString).join(
" or ",
);
this.message = `at line ${colRow.row + 1}, column ${colRow.col + 1}:\n\n` +
`expected ${expectedPatternsText}, got ${patternToString(got)}\n\n` +
parser.getAroundText(parser.loc, length);
}
get got() {
const parser = this.parser;
for (const mistakePattern of this.mistakePatterns) {
const token = parser.try(mistakePattern);
if (token) return token.text;
}
return parser.input.charAt(parser.loc) || eof;
}
get colRow() {
return this.parser.offsetToColRow(this.parser.loc);
}
}
function patternToString(pattern: Pattern) {
if (pattern === eof) return "<EOF>";
if (typeof pattern === "string") return JSON.stringify(pattern);
return pattern.toString();
}
function offsetToColRow(lines: string[], offset: number) {
let row = 0;
let col = 0;
for (let i = 0; i < lines.length; i++) {
const line = lines[i];
if (offset < line.length + 1) {
row = i;
col = offset;
break;
}
offset -= line.length + 1;
}
return { col, row };
}
function colRowToOffset(lines: string[], { col, row }: ColRow) {
let offset = 0;
for (let i = 0; i < row; i++) {
offset += lines[i].length + 1;
}
return offset + col;
}
function getAroundText(
lines: string[],
loc: number,
length: number = 1,
window: number = 5,
) {
const colRow = offsetToColRow(lines, loc);
const headCount = Math.min(1, (window >> 1) + (window % 2));
const tailCount = window >> 1;
const headStart = Math.max(0, colRow.row - headCount - 1);
const headEnd = colRow.row + 1;
const tailStart = colRow.row + 1;
const tailEnd = colRow.row + tailCount + 1;
const heads = lines.slice(headStart, headEnd);
const tails = lines.slice(tailStart, tailEnd);
const lineNumberDigitCount = tailEnd.toString().length;
const headTexts = heads.map((line, index) => {
const lineNumber = index + headStart + 1;
const lineNumberText = lineNumber.toString().padStart(
lineNumberDigitCount + 1,
);
return lineNumberText + " | " + line;
}).join("\n");
const tailTexts = tails.map((line, index) => {
const lineNumber = index + tailStart + 1;
const lineNumberText = lineNumber.toString().padStart(
lineNumberDigitCount + 1,
);
return lineNumberText + " | " + line;
}).join("\n");
return [
headTexts,
(new Array(lineNumberDigitCount + 1 + 1)).join(" ") + " | " +
(new Array(colRow.col + 1)).join(" ") +
(new Array(length + 1)).join("^"),
tailTexts,
].join("\n");
}