@mapwhit/style-expressions/lib/expression/definitions/let.js

Process expressions in map style.

export default class Let {
  constructor(bindings, result) {
    this.type = result.type;
    this.bindings = [].concat(bindings);
    this.result = result;
  }

  evaluate(ctx) {
    return this.result.evaluate(ctx);
  }

  eachChild(fn) {
    for (const binding of this.bindings) {
      fn(binding[1]);
    }
    fn(this.result);
  }

  static parse(args, context) {
    if (args.length < 4) return context.error(`Expected at least 3 arguments, but found ${args.length - 1} instead.`);

    const bindings = [];
    for (let i = 1; i < args.length - 1; i += 2) {
      const name = args[i];

      if (typeof name !== 'string') {
        return context.error(`Expected string, but found ${typeof name} instead.`, i);
      }

      if (/[^a-zA-Z0-9_]/.test(name)) {
        return context.error(`Variable names must contain only alphanumeric characters or '_'.`, i);
      }

      const value = context.parse(args[i + 1], i + 1);
      if (!value) return null;

      bindings.push([name, value]);
    }

    const result = context.parse(args[args.length - 1], args.length - 1, context.expectedType, bindings);
    if (!result) return null;

    return new Let(bindings, result);
  }

  possibleOutputs() {
    return this.result.possibleOutputs();
  }
}