/
compileGrammar.ts
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/
compileGrammar.ts
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import fs from "fs";
import { RawGrammar } from "./parseGrammar";
import Token from "./Token";
import Stack from "./Stack";
interface BaseRule {
name: string;
optional?: boolean;
repeats?: boolean;
}
export interface LiteralRule extends BaseRule {
__type: "literal";
value: string;
}
export interface RefRule extends BaseRule {
__type: "ref";
target: string;
}
export interface AlternativesRule extends BaseRule {
__type: "or";
rules: Array<Rule>;
}
export interface ComplexRule extends BaseRule {
__type: "complex";
rules: Array<Rule>;
}
export type Rule = ComplexRule | LiteralRule | AlternativesRule | RefRule;
export type CompiledGrammar = Record<string, Rule>;
export function canCompileRule(
allRules: Rule[],
rule: Rule,
seen: string[] = []
): boolean {
if (seen.includes(rule.name)) {
return false;
}
switch (rule.__type) {
case "complex": {
seen.push(rule.name);
for (const subRule of rule.rules) {
if (subRule.__type === "literal") {
return false;
}
if (!canCompileRule(allRules, subRule, seen)) {
return false;
}
}
break;
}
case "or": {
for (const subRule of rule.rules) {
if (!canCompileRule(allRules, subRule, seen)) {
return false;
}
}
break;
}
case "ref": {
const target = allRules.find(r => r.name === rule.target);
return !!target && canCompileRule(allRules, target, seen);
}
}
return true;
}
function resolveRule(fragment: string): Partial<Rule> {
let resolvedRule: Partial<Rule>;
if (fragment.endsWith("*")) {
resolvedRule = resolveRule(fragment.substring(0, fragment.length - 1));
resolvedRule.optional = true;
resolvedRule.repeats = true;
} else if (fragment.endsWith("+")) {
resolvedRule = resolveRule(fragment.substring(0, fragment.length - 1));
resolvedRule.repeats = true;
} else if (fragment.endsWith("?")) {
resolvedRule = resolveRule(fragment.substring(0, fragment.length - 1));
resolvedRule.optional = true;
} else if (fragment.startsWith('"')) {
const value = fragment.substring(1, fragment.length - 1);
resolvedRule = { __type: "literal", value };
} else if (fragment.startsWith("(")) {
resolvedRule = resolveRule(fragment.substring(1, fragment.length - 1));
} else {
resolvedRule = { __type: "ref", target: fragment };
}
return resolvedRule;
}
function parseRule(rawRulePart: string): Partial<Rule> {
const parts = rawRulePart.split(" ");
const ruleParts: Array<Rule> = [];
for (let part of parts) {
const rule = resolveRule(part);
ruleParts.push(rule as Rule);
}
if (ruleParts.length === 1) {
return ruleParts[0];
}
return { __type: "complex", rules: ruleParts };
}
function writeDeclarations(grammar: Rule[]) {
const out = fs.openSync("./grammar.compiled.ts", "w");
fs.writeSync(out, "export enum Symbols {\n");
for (let idx = 0; idx < grammar.length; idx++) {
const rule = grammar[idx];
fs.writeSync(out, ` ${rule.name} = '${rule.name}',\n`);
}
fs.writeSync(out, "};\n");
fs.closeSync(out);
}
interface CompileGrammarOptions {
writeDeclarationFile?: boolean;
}
export default function compileGrammar(
rawGrammar: RawGrammar,
opts: CompileGrammarOptions
): Rule[] {
const grammar: Rule[] = [];
for (let [ruleName, rawRule] of rawGrammar) {
const rule = rawRule.replace("\n", "").trim();
const alternatives = rule.split(/(?: )*\|(?: )*/g);
let compiledRule: Partial<Rule> = { name: ruleName };
if (alternatives.length > 1) {
compiledRule = {
...compiledRule,
__type: "or",
rules: []
} as AlternativesRule;
for (let idx in alternatives) {
const rawAlt = alternatives[idx];
const alternative = parseRule(rawAlt);
compiledRule.rules!.push({
name:
alternative.__type === "ref"
? alternative.target
: `${ruleName}${idx}`,
...alternative
} as Rule);
}
} else {
compiledRule = { ...compiledRule, ...parseRule(alternatives[0]) };
}
grammar.push(compiledRule as Rule);
}
if (opts.writeDeclarationFile) {
writeDeclarations(grammar);
}
return grammar;
}