sexp-template/src/tokenStream.js

const OsloError = require('./osloError')

module.exports = class TokenStream {
  constructor() {
    this.tokens = []
    this.position = 0
  }

  advance() {
    this.position++
  }

  eat(tokenType) {
    let token = this.peek()

    if (token && token.type === tokenType) {
      this.advance()
      return token
    }

    this.error = new OsloError({
      line: token.line,
      message: `Encountered an unexpected ${
        token.type
      } while looking for a ${tokenType}.`,
    })
  }

  peek(step = 0) {
    return this.tokens[this.position + step]
  }
}