export function new_env(outer={}, binds=[], exprs=[]) {
    var e = Object.setPrototypeOf({}, outer)
    // Bind symbols in binds to values in exprs
    for (var i=0; i<binds.length; i++) {
        if (Symbol.keyFor(binds[i]) === "&") {
            e[binds[i+1]] = exprs.slice(i) // variable length arguments
            break
        } else {
            e[binds[i]] = exprs[i]
        }
    }
    return e
}
export const env_get = (env, sym) => {
    if (sym in env) {
        return env[sym]
    } else {
        throw Error(`'${Symbol.keyFor(sym)}' not found`)
    }
}
export const env_set = (env, sym, val) => env[sym] = val