import {types as tt} from "./tokentype"
  import {Parser} from "./state"
  import {lineBreak, skipWhiteSpace} from "./whitespace"
  import {isIdentifierStart, isIdentifierChar} from "./identifier"
  import {has} from "./util"
  import {DestructuringErrors} from "./parseutil"
  
  const pp = Parser.prototype
  
  // ### Statement parsing
  
  // Parse a program. Initializes the parser, reads any number of
  // statements, and wraps them in a Program node.  Optionally takes a
  // `program` argument.  If present, the statements will be appended
  // to its body instead of creating a new node.
  
  pp.parseTopLevel = function(node) {
    let exports = {}
    if (!node.body) node.body = []
    while (this.type !== tt.eof) {
      let stmt = this.parseStatement(true, true, exports)
      node.body.push(stmt)
    }
    this.next()
    if (this.options.ecmaVersion >= 6) {
      node.sourceType = this.options.sourceType
    }
    return this.finishNode(node, "Program")
  }
  
  const loopLabel = {kind: "loop"}, switchLabel = {kind: "switch"}
  
  pp.isLet = function() {
    if (this.type !== tt.name || this.options.ecmaVersion < 6 || this.value != "let") return false
    skipWhiteSpace.lastIndex = this.pos
    let skip = skipWhiteSpace.exec(this.input)
    let next = this.pos + skip[0].length, nextCh = this.input.charCodeAt(next)
    if (nextCh === 91 || nextCh == 123) return true // '{' and '['
    if (isIdentifierStart(nextCh, true)) {
      let pos = next + 1
      while (isIdentifierChar(this.input.charCodeAt(pos), true)) ++pos
      let ident = this.input.slice(next, pos)
      if (!this.isKeyword(ident)) return true
    }
    return false
  }
  
  // check 'async [no LineTerminator here] function'
  // - 'async /*foo*/ function' is OK.
  // - 'async /*
  */ function' is invalid.
  pp.isAsyncFunction = function() {
    if (this.type !== tt.name || this.options.ecmaVersion < 8 || this.value != "async")
      return false
  
    skipWhiteSpace.lastIndex = this.pos
    let skip = skipWhiteSpace.exec(this.input)
    let next = this.pos + skip[0].length
    return !lineBreak.test(this.input.slice(this.pos, next)) &&
      this.input.slice(next, next + 8) === "function" &&
      (next + 8 == this.input.length || !isIdentifierChar(this.input.charAt(next + 8)))
  }
  
  // Parse a single statement.
  //
  // If expecting a statement and finding a slash operator, parse a
  // regular expression literal. This is to handle cases like
  // `if (foo) /blah/.exec(foo)`, where looking at the previous token
  // does not help.
  
  pp.parseStatement = function(declaration, topLevel, exports) {
    let starttype = this.type, node = this.startNode(), kind
  
    if (this.isLet()) {
      starttype = tt._var
      kind = "let"
    }
  
    // Most types of statements are recognized by the keyword they
    // start with. Many are trivial to parse, some require a bit of
    // complexity.
  
    switch (starttype) {
    case tt._break: case tt._continue: return this.parseBreakContinueStatement(node, starttype.keyword)
    case tt._debugger: return this.parseDebuggerStatement(node)
    case tt._do: return this.parseDoStatement(node)
    case tt._for: return this.parseForStatement(node)
    case tt._function:
      if (!declaration && this.options.ecmaVersion >= 6) this.unexpected()
      return this.parseFunctionStatement(node, false)
    case tt._class:
      if (!declaration) this.unexpected()
      return this.parseClass(node, true)
    case tt._if: return this.parseIfStatement(node)
    case tt._return: return this.parseReturnStatement(node)
    case tt._switch: return this.parseSwitchStatement(node)
    case tt._throw: return this.parseThrowStatement(node)
    case tt._try: return this.parseTryStatement(node)
    case tt._const: case tt._var:
      kind = kind || this.value
      if (!declaration && kind != "var") this.unexpected()
      return this.parseVarStatement(node, kind)
    case tt._while: return this.parseWhileStatement(node)
    case tt._with: return this.parseWithStatement(node)
    case tt.braceL: return this.parseBlock()
    case tt.semi: return this.parseEmptyStatement(node)
    case tt._export:
    case tt._import:
      if (!this.options.allowImportExportEverywhere) {
        if (!topLevel)
          this.raise(this.start, "'import' and 'export' may only appear at the top level")
        if (!this.inModule)
          this.raise(this.start, "'import' and 'export' may appear only with 'sourceType: module'")
      }
      return starttype === tt._import ? this.parseImport(node) : this.parseExport(node, exports)
  
      // If the statement does not start with a statement keyword or a
      // brace, it's an ExpressionStatement or LabeledStatement. We
      // simply start parsing an expression, and afterwards, if the
      // next token is a colon and the expression was a simple
      // Identifier node, we switch to interpreting it as a label.
    default:
      if (this.isAsyncFunction() && declaration) {
        this.next()
        return this.parseFunctionStatement(node, true)
      }
  
      let maybeName = this.value, expr = this.parseExpression()
      if (starttype === tt.name && expr.type === "Identifier" && this.eat(tt.colon))
        return this.parseLabeledStatement(node, maybeName, expr)
      else return this.parseExpressionStatement(node, expr)
    }
  }
  
  pp.parseBreakContinueStatement = function(node, keyword) {
    let isBreak = keyword == "break"
    this.next()
    if (this.eat(tt.semi) || this.insertSemicolon()) node.label = null
    else if (this.type !== tt.name) this.unexpected()
    else {
      node.label = this.parseIdent()
      this.semicolon()
    }
  
    // Verify that there is an actual destination to break or
    // continue to.
    let i = 0
    for (; i < this.labels.length; ++i) {
      let lab = this.labels[i]
      if (node.label == null || lab.name === node.label.name) {
        if (lab.kind != null && (isBreak || lab.kind === "loop")) break
        if (node.label && isBreak) break
      }
    }
    if (i === this.labels.length) this.raise(node.start, "Unsyntactic " + keyword)
    return this.finishNode(node, isBreak ? "BreakStatement" : "ContinueStatement")
  }
  
  pp.parseDebuggerStatement = function(node) {
    this.next()
    this.semicolon()
    return this.finishNode(node, "DebuggerStatement")
  }
  
  pp.parseDoStatement = function(node) {
    this.next()
    this.labels.push(loopLabel)
    node.body = this.parseStatement(false)
    this.labels.pop()
    this.expect(tt._while)
    node.test = this.parseParenExpression()
    if (this.options.ecmaVersion >= 6)
      this.eat(tt.semi)
    else
      this.semicolon()
    return this.finishNode(node, "DoWhileStatement")
  }
  
  // Disambiguating between a `for` and a `for`/`in` or `for`/`of`
  // loop is non-trivial. Basically, we have to parse the init `var`
  // statement or expression, disallowing the `in` operator (see
  // the second parameter to `parseExpression`), and then check
  // whether the next token is `in` or `of`. When there is no init
  // part (semicolon immediately after the opening parenthesis), it
  // is a regular `for` loop.
  
  pp.parseForStatement = function(node) {
    this.next()
    this.labels.push(loopLabel)
    this.enterLexicalScope()
    this.expect(tt.parenL)
    if (this.type === tt.semi) return this.parseFor(node, null)
    let isLet = this.isLet()
    if (this.type === tt._var || this.type === tt._const || isLet) {
      let init = this.startNode(), kind = isLet ? "let" : this.value
      this.next()
      this.parseVar(init, true, kind)
      this.finishNode(init, "VariableDeclaration")
      if ((this.type === tt._in || (this.options.ecmaVersion >= 6 && this.isContextual("of"))) && init.declarations.length === 1 &&
          !(kind !== "var" && init.declarations[0].init))
        return this.parseForIn(node, init)
      return this.parseFor(node, init)
    }
    let refDestructuringErrors = new DestructuringErrors
    let init = this.parseExpression(true, refDestructuringErrors)
    if (this.type === tt._in || (this.options.ecmaVersion >= 6 && this.isContextual("of"))) {
      this.toAssignable(init)
      this.checkLVal(init)
      this.checkPatternErrors(refDestructuringErrors, true)
      return this.parseForIn(node, init)
    } else {
      this.checkExpressionErrors(refDestructuringErrors, true)
    }
    return this.parseFor(node, init)
  }
  
  pp.parseFunctionStatement = function(node, isAsync) {
    this.next()
    return this.parseFunction(node, true, false, isAsync)
  }
  
  pp.isFunction = function() {
    return this.type === tt._function || this.isAsyncFunction()
  }
  
  pp.parseIfStatement = function(node) {
    this.next()
    node.test = this.parseParenExpression()
    // allow function declarations in branches, but only in non-strict mode
    node.consequent = this.parseStatement(!this.strict && this.isFunction())
    node.alternate = this.eat(tt._else) ? this.parseStatement(!this.strict && this.isFunction()) : null
    return this.finishNode(node, "IfStatement")
  }
  
  pp.parseReturnStatement = function(node) {
    if (!this.inFunction && !this.options.allowReturnOutsideFunction)
      this.raise(this.start, "'return' outside of function")
    this.next()
  
    // In `return` (and `break`/`continue`), the keywords with
    // optional arguments, we eagerly look for a semicolon or the
    // possibility to insert one.
  
    if (this.eat(tt.semi) || this.insertSemicolon()) node.argument = null
    else { node.argument = this.parseExpression(); this.semicolon() }
    return this.finishNode(node, "ReturnStatement")
  }
  
  pp.parseSwitchStatement = function(node) {
    this.next()
    node.discriminant = this.parseParenExpression()
    node.cases = []
    this.expect(tt.braceL)
    this.labels.push(switchLabel)
    this.enterLexicalScope()
  
    // Statements under must be grouped (by label) in SwitchCase
    // nodes. `cur` is used to keep the node that we are currently
    // adding statements to.
  
    let cur
    for (let sawDefault = false; this.type != tt.braceR;) {
      if (this.type === tt._case || this.type === tt._default) {
        let isCase = this.type === tt._case
        if (cur) this.finishNode(cur, "SwitchCase")
        node.cases.push(cur = this.startNode())
        cur.consequent = []
        this.next()
        if (isCase) {
          cur.test = this.parseExpression()
        } else {
          if (sawDefault) this.raiseRecoverable(this.lastTokStart, "Multiple default clauses")
          sawDefault = true
          cur.test = null
        }
        this.expect(tt.colon)
      } else {
        if (!cur) this.unexpected()
        cur.consequent.push(this.parseStatement(true))
      }
    }
    this.exitLexicalScope()
    if (cur) this.finishNode(cur, "SwitchCase")
    this.next() // Closing brace
    this.labels.pop()
    return this.finishNode(node, "SwitchStatement")
  }
  
  pp.parseThrowStatement = function(node) {
    this.next()
    if (lineBreak.test(this.input.slice(this.lastTokEnd, this.start)))
      this.raise(this.lastTokEnd, "Illegal newline after throw")
    node.argument = this.parseExpression()
    this.semicolon()
    return this.finishNode(node, "ThrowStatement")
  }
  
  // Reused empty array added for node fields that are always empty.
  
  const empty = []
  
  pp.parseTryStatement = function(node) {
    this.next()
    node.block = this.parseBlock()
    node.handler = null
    if (this.type === tt._catch) {
      let clause = this.startNode()
      this.next()
      this.expect(tt.parenL)
      clause.param = this.parseBindingAtom()
      this.enterLexicalScope()
      this.checkLVal(clause.param, "let")
      this.expect(tt.parenR)
      clause.body = this.parseBlock(false)
      this.exitLexicalScope()
      node.handler = this.finishNode(clause, "CatchClause")
    }
    node.finalizer = this.eat(tt._finally) ? this.parseBlock() : null
    if (!node.handler && !node.finalizer)
      this.raise(node.start, "Missing catch or finally clause")
    return this.finishNode(node, "TryStatement")
  }
  
  pp.parseVarStatement = function(node, kind) {
    this.next()
    this.parseVar(node, false, kind)
    this.semicolon()
    return this.finishNode(node, "VariableDeclaration")
  }
  
  pp.parseWhileStatement = function(node) {
    this.next()
    node.test = this.parseParenExpression()
    this.labels.push(loopLabel)
    node.body = this.parseStatement(false)
    this.labels.pop()
    return this.finishNode(node, "WhileStatement")
  }
  
  pp.parseWithStatement = function(node) {
    if (this.strict) this.raise(this.start, "'with' in strict mode")
    this.next()
    node.object = this.parseParenExpression()
    node.body = this.parseStatement(false)
    return this.finishNode(node, "WithStatement")
  }
  
  pp.parseEmptyStatement = function(node) {
    this.next()
    return this.finishNode(node, "EmptyStatement")
  }
  
  pp.parseLabeledStatement = function(node, maybeName, expr) {
    for (let i = 0; i < this.labels.length; ++i)
      if (this.labels[i].name === maybeName) this.raise(expr.start, "Label '" + maybeName + "' is already declared")
    let kind = this.type.isLoop ? "loop" : this.type === tt._switch ? "switch" : null
    for (let i = this.labels.length - 1; i >= 0; i--) {
      let label = this.labels[i]
      if (label.statementStart == node.start) {
        label.statementStart = this.start
        label.kind = kind
      } else break
    }
    this.labels.push({name: maybeName, kind: kind, statementStart: this.start})
    node.body = this.parseStatement(true)
    if (node.body.type == "ClassDeclaration" ||
        node.body.type == "VariableDeclaration" && node.body.kind != "var" ||
        node.body.type == "FunctionDeclaration" && (this.strict || node.body.generator))
      this.raiseRecoverable(node.body.start, "Invalid labeled declaration")
    this.labels.pop()
    node.label = expr
    return this.finishNode(node, "LabeledStatement")
  }
  
  pp.parseExpressionStatement = function(node, expr) {
    node.expression = expr
    this.semicolon()
    return this.finishNode(node, "ExpressionStatement")
  }
  
  // Parse a semicolon-enclosed block of statements, handling `"use
  // strict"` declarations when `allowStrict` is true (used for
  // function bodies).
  
  pp.parseBlock = function(createNewLexicalScope = true) {
    let node = this.startNode()
    node.body = []
    this.expect(tt.braceL)
    if (createNewLexicalScope) {
      this.enterLexicalScope()
    }
    while (!this.eat(tt.braceR)) {
      let stmt = this.parseStatement(true)
      node.body.push(stmt)
    }
    if (createNewLexicalScope) {
      this.exitLexicalScope()
    }
    return this.finishNode(node, "BlockStatement")
  }
  
  // Parse a regular `for` loop. The disambiguation code in
  // `parseStatement` will already have parsed the init statement or
  // expression.
  
  pp.parseFor = function(node, init) {
    node.init = init
    this.expect(tt.semi)
    node.test = this.type === tt.semi ? null : this.parseExpression()
    this.expect(tt.semi)
    node.update = this.type === tt.parenR ? null : this.parseExpression()
    this.expect(tt.parenR)
    this.exitLexicalScope()
    node.body = this.parseStatement(false)
    this.labels.pop()
    return this.finishNode(node, "ForStatement")
  }
  
  // Parse a `for`/`in` and `for`/`of` loop, which are almost
  // same from parser's perspective.
  
  pp.parseForIn = function(node, init) {
    let type = this.type === tt._in ? "ForInStatement" : "ForOfStatement"
    this.next()
    node.left = init
    node.right = this.parseExpression()
    this.expect(tt.parenR)
    this.exitLexicalScope()
    node.body = this.parseStatement(false)
    this.labels.pop()
    return this.finishNode(node, type)
  }
  
  // Parse a list of variable declarations.
  
  pp.parseVar = function(node, isFor, kind) {
    node.declarations = []
    node.kind = kind
    for (;;) {
      let decl = this.startNode()
      this.parseVarId(decl, kind)
      if (this.eat(tt.eq)) {
        decl.init = this.parseMaybeAssign(isFor)
      } else if (kind === "const" && !(this.type === tt._in || (this.options.ecmaVersion >= 6 && this.isContextual("of")))) {
        this.unexpected()
      } else if (decl.id.type != "Identifier" && !(isFor && (this.type === tt._in || this.isContextual("of")))) {
        this.raise(this.lastTokEnd, "Complex binding patterns require an initialization value")
      } else {
        decl.init = null
      }
      node.declarations.push(this.finishNode(decl, "VariableDeclarator"))
      if (!this.eat(tt.comma)) break
    }
    return node
  }
  
  pp.parseVarId = function(decl, kind) {
    decl.id = this.parseBindingAtom(kind)
    this.checkLVal(decl.id, kind, false)
  }
  
  // Parse a function declaration or literal (depending on the
  // `isStatement` parameter).
  
  pp.parseFunction = function(node, isStatement, allowExpressionBody, isAsync) {
    this.initFunction(node)
    if (this.options.ecmaVersion >= 6 && !isAsync)
      node.generator = this.eat(tt.star)
    if (this.options.ecmaVersion >= 8)
      node.async = !!isAsync
  
    if (isStatement) {
      node.id = isStatement === "nullableID" && this.type != tt.name ? null : this.parseIdent()
      if (node.id) {
        this.checkLVal(node.id, "var")
      }
    }
  
    let oldInGen = this.inGenerator, oldInAsync = this.inAsync,
        oldYieldPos = this.yieldPos, oldAwaitPos = this.awaitPos, oldInFunc = this.inFunction
    this.inGenerator = node.generator
    this.inAsync = node.async
    this.yieldPos = 0
    this.awaitPos = 0
    this.inFunction = true
    this.enterFunctionScope()
  
    if (!isStatement)
      node.id = this.type == tt.name ? this.parseIdent() : null
  
    this.parseFunctionParams(node)
    this.parseFunctionBody(node, allowExpressionBody)
  
    this.inGenerator = oldInGen
    this.inAsync = oldInAsync
    this.yieldPos = oldYieldPos
    this.awaitPos = oldAwaitPos
    this.inFunction = oldInFunc
    return this.finishNode(node, isStatement ? "FunctionDeclaration" : "FunctionExpression")
  }
  
  pp.parseFunctionParams = function(node) {
    this.expect(tt.parenL)
    node.params = this.parseBindingList(tt.parenR, false, this.options.ecmaVersion >= 8, true)
    this.checkYieldAwaitInDefaultParams()
  }
  
  // Parse a class declaration or literal (depending on the
  // `isStatement` parameter).
  
  pp.parseClass = function(node, isStatement) {
    this.next()
  
    this.parseClassId(node, isStatement)
    this.parseClassSuper(node)
    let classBody = this.startNode()
    let hadConstructor = false
    classBody.body = []
    this.expect(tt.braceL)
    while (!this.eat(tt.braceR)) {
      if (this.eat(tt.semi)) continue
      let method = this.startNode()
      let isGenerator = this.eat(tt.star)
      let isAsync = false
      let isMaybeStatic = this.type === tt.name && this.value === "static"
      this.parsePropertyName(method)
      method.static = isMaybeStatic && this.type !== tt.parenL
      if (method.static) {
        if (isGenerator) this.unexpected()
        isGenerator = this.eat(tt.star)
        this.parsePropertyName(method)
      }
      if (this.options.ecmaVersion >= 8 && !isGenerator && !method.computed &&
          method.key.type === "Identifier" && method.key.name === "async" && this.type !== tt.parenL &&
          !this.canInsertSemicolon()) {
        isAsync = true
        this.parsePropertyName(method)
      }
      method.kind = "method"
      let isGetSet = false
      if (!method.computed) {
        let {key} = method
        if (!isGenerator && !isAsync && key.type === "Identifier" && this.type !== tt.parenL && (key.name === "get" || key.name === "set")) {
          isGetSet = true
          method.kind = key.name
          key = this.parsePropertyName(method)
        }
        if (!method.static && (key.type === "Identifier" && key.name === "constructor" ||
            key.type === "Literal" && key.value === "constructor")) {
          if (hadConstructor) this.raise(key.start, "Duplicate constructor in the same class")
          if (isGetSet) this.raise(key.start, "Constructor can't have get/set modifier")
          if (isGenerator) this.raise(key.start, "Constructor can't be a generator")
          if (isAsync) this.raise(key.start, "Constructor can't be an async method")
          method.kind = "constructor"
          hadConstructor = true
        }
      }
      this.parseClassMethod(classBody, method, isGenerator, isAsync)
      if (isGetSet) {
        let paramCount = method.kind === "get" ? 0 : 1
        if (method.value.params.length !== paramCount) {
          let start = method.value.start
          if (method.kind === "get")
            this.raiseRecoverable(start, "getter should have no params")
          else
            this.raiseRecoverable(start, "setter should have exactly one param")
        } else {
          if (method.kind === "set" && method.value.params[0].type === "RestElement")
            this.raiseRecoverable(method.value.params[0].start, "Setter cannot use rest params")
        }
      }
    }
    node.body = this.finishNode(classBody, "ClassBody")
    return this.finishNode(node, isStatement ? "ClassDeclaration" : "ClassExpression")
  }
  
  pp.parseClassMethod = function(classBody, method, isGenerator, isAsync) {
    method.value = this.parseMethod(isGenerator, isAsync)
    classBody.body.push(this.finishNode(method, "MethodDefinition"))
  }
  
  pp.parseClassId = function(node, isStatement) {
    node.id = this.type === tt.name ? this.parseIdent() : isStatement === true ? this.unexpected() : null
  }
  
  pp.parseClassSuper = function(node) {
    node.superClass = this.eat(tt._extends) ? this.parseExprSubscripts() : null
  }
  
  // Parses module export declaration.
  
  pp.parseExport = function(node, exports) {
    this.next()
    // export * from '...'
    if (this.eat(tt.star)) {
      this.expectContextual("from")
      node.source = this.type === tt.string ? this.parseExprAtom() : this.unexpected()
      this.semicolon()
      return this.finishNode(node, "ExportAllDeclaration")
    }
    if (this.eat(tt._default)) { // export default ...
      this.checkExport(exports, "default", this.lastTokStart)
      let isAsync
      if (this.type === tt._function || (isAsync = this.isAsyncFunction())) {
        let fNode = this.startNode()
        this.next()
        if (isAsync) this.next()
        node.declaration = this.parseFunction(fNode, "nullableID", false, isAsync)
      } else if (this.type === tt._class) {
        let cNode = this.startNode()
        node.declaration = this.parseClass(cNode, "nullableID")
      } else {
        node.declaration = this.parseMaybeAssign()
        this.semicolon()
      }
      return this.finishNode(node, "ExportDefaultDeclaration")
    }
    // export var|const|let|function|class ...
    if (this.shouldParseExportStatement()) {
      node.declaration = this.parseStatement(true)
      if (node.declaration.type === "VariableDeclaration")
        this.checkVariableExport(exports, node.declaration.declarations)
      else
        this.checkExport(exports, node.declaration.id.name, node.declaration.id.start)
      node.specifiers = []
      node.source = null
    } else { // export { x, y as z } [from '...']
      node.declaration = null
      node.specifiers = this.parseExportSpecifiers(exports)
      if (this.eatContextual("from")) {
        node.source = this.type === tt.string ? this.parseExprAtom() : this.unexpected()
      } else {
        // check for keywords used as local names
        for (let i = 0; i < node.specifiers.length; i++) {
          if (this.keywords.test(node.specifiers[i].local.name) || this.reservedWords.test(node.specifiers[i].local.name)) {
            this.unexpected(node.specifiers[i].local.start)
          }
        }
  
        node.source = null
      }
      this.semicolon()
    }
    return this.finishNode(node, "ExportNamedDeclaration")
  }
  
  pp.checkExport = function(exports, name, pos) {
    if (!exports) return
    if (has(exports, name))
      this.raiseRecoverable(pos, "Duplicate export '" + name + "'")
    exports[name] = true
  }
  
  pp.checkPatternExport = function(exports, pat) {
    let type = pat.type
    if (type == "Identifier")
      this.checkExport(exports, pat.name, pat.start)
    else if (type == "ObjectPattern")
      for (let i = 0; i < pat.properties.length; ++i)
        this.checkPatternExport(exports, pat.properties[i].value)
    else if (type == "ArrayPattern")
      for (let i = 0; i < pat.elements.length; ++i) {
        let elt = pat.elements[i]
        if (elt) this.checkPatternExport(exports, elt)
      }
    else if (type == "AssignmentPattern")
      this.checkPatternExport(exports, pat.left)
    else if (type == "ParenthesizedExpression")
      this.checkPatternExport(exports, pat.expression)
  }
  
  pp.checkVariableExport = function(exports, decls) {
    if (!exports) return
    for (let i = 0; i < decls.length; i++)
      this.checkPatternExport(exports, decls[i].id)
  }
  
  pp.shouldParseExportStatement = function() {
    return this.type.keyword === "var" ||
      this.type.keyword === "const" ||
      this.type.keyword === "class" ||
      this.type.keyword === "function" ||
      this.isLet() ||
      this.isAsyncFunction()
  }
  
  // Parses a comma-separated list of module exports.
  
  pp.parseExportSpecifiers = function(exports) {
    let nodes = [], first = true
    // export { x, y as z } [from '...']
    this.expect(tt.braceL)
    while (!this.eat(tt.braceR)) {
      if (!first) {
        this.expect(tt.comma)
        if (this.afterTrailingComma(tt.braceR)) break
      } else first = false
  
      let node = this.startNode()
      node.local = this.parseIdent(true)
      node.exported = this.eatContextual("as") ? this.parseIdent(true) : node.local
      this.checkExport(exports, node.exported.name, node.exported.start)
      nodes.push(this.finishNode(node, "ExportSpecifier"))
    }
    return nodes
  }
  
  // Parses import declaration.
  
  pp.parseImport = function(node) {
    this.next()
    // import '...'
    if (this.type === tt.string) {
      node.specifiers = empty
      node.source = this.parseExprAtom()
    } else {
      node.specifiers = this.parseImportSpecifiers()
      this.expectContextual("from")
      node.source = this.type === tt.string ? this.parseExprAtom() : this.unexpected()
    }
    this.semicolon()
    return this.finishNode(node, "ImportDeclaration")
  }
  
  // Parses a comma-separated list of module imports.
  
  pp.parseImportSpecifiers = function() {
    let nodes = [], first = true
    if (this.type === tt.name) {
      // import defaultObj, { x, y as z } from '...'
      let node = this.startNode()
      node.local = this.parseIdent()
      this.checkLVal(node.local, "let")
      nodes.push(this.finishNode(node, "ImportDefaultSpecifier"))
      if (!this.eat(tt.comma)) return nodes
    }
    if (this.type === tt.star) {
      let node = this.startNode()
      this.next()
      this.expectContextual("as")
      node.local = this.parseIdent()
      this.checkLVal(node.local, "let")
      nodes.push(this.finishNode(node, "ImportNamespaceSpecifier"))
      return nodes
    }
    this.expect(tt.braceL)
    while (!this.eat(tt.braceR)) {
      if (!first) {
        this.expect(tt.comma)
        if (this.afterTrailingComma(tt.braceR)) break
      } else first = false
  
      let node = this.startNode()
      node.imported = this.parseIdent(true)
      if (this.eatContextual("as")) {
        node.local = this.parseIdent()
      } else {
        node.local = node.imported
        if (this.isKeyword(node.local.name)) this.unexpected(node.local.start)
        if (this.reservedWordsStrict.test(node.local.name)) this.raiseRecoverable(node.local.start, "The keyword '" + node.local.name + "' is reserved")
      }
      this.checkLVal(node.local, "let")
      nodes.push(this.finishNode(node, "ImportSpecifier"))
    }
    return nodes
  }