formal-language/grammar

import EW from './EW.js';

export default function alphabet(productions) {
    const abc = new Set();

    for (const unit of productions.values()) {
        for (const rule of unit.values()) {
            if (rule.length === 0) abc.add(EW);
            else
                for (const part of rule)
                    if (part.type === 'leaf') abc.add(part.terminal);
        }
    }

    return abc;
}