AST使った計算機 (引数に"1 * 3"みたいに式を指定)

index.js

const babylon = require('babylon')

const parse = (source) => {
    try {
        const ast = babylon.parse(source)
        delete ast.tokens
        return {ast}
    } catch (err) {
        return {error: err}
    }
}
if (process.argv.length <= 2) {
    console.error('引数に計算式かいてください')
    process.exit(1)
}
const {ast} = parse(process.argv[2])

const replacer = (key, value) => {
    if (!key) {
        return value
    }
    if (/^[0-9]+$/.test(key)) {
        return value
    }
    return (['type', 'program', 'body', 'expression','left', 'right']).indexOf(key) === -1 ? undefined : value
}
// console.log(JSON.stringify(ast, replacer, '  '))


const walker = (node, warkers) => {
    if (!(node.type in walkers)) {
        throw new Error('対応してないtype', node.type)
    }

    return walkers[node.type](node)
}

const walkers = {
    'File': node => walker(node.program),
    'Program': node => {
        node.body.forEach(value => console.log(walker(value)))
        return null
    },
    'ExpressionStatement': node => walker(node.expression),
    'BinaryExpression': node => {
        const left = walker(node.left)
        const right = walker(node.right)
        switch (node.operator) {
            case '+': return left + right
            case '*': return left * right
            case '-': return left - right
            case '/': return left / right
            case '%': return left % right
            default: throw new Error('対応してない二項演算子')
        }
    },
    'NumericLiteral': node => node.value
}

walker(ast, walkers)