(function (global, factory) {
  typeof exports === 'object' && typeof module !== 'undefined' ? factory(exports) :
  typeof define === 'function' && define.amd ? define(['exports'], factory) :
  (factory((global.acorn = global.acorn || {}, global.acorn.walk = global.acorn.walk || {})));
}(this, function (exports) { 'use strict';

  // AST walker module for Mozilla Parser API compatible trees

  // A simple walk is one where you simply specify callbacks to be
  // called on specific nodes. The last two arguments are optional. A
  // simple use would be
  //
  //     walk.simple(myTree, {
  //         Expression: function(node) { ... }
  //     });
  //
  // to do something with all expressions. All Parser API node types
  // can be used to identify node types, as well as Expression,
  // Statement, and ScopeBody, which denote categories of nodes.
  //
  // The base argument can be used to pass a custom (recursive)
  // walker, and state can be used to give this walked an initial
  // state.

  function simple(node, visitors, base, state, override) {
    if (!base) base = exports.base
    ;(function c(node, st, override) {
      var type = override || node.type, found = visitors[type]
      base[type](node, st, c)
      if (found) found(node, st)
    })(node, state, override)
  }

  // An ancestor walk keeps an array of ancestor nodes (including the
  // current node) and passes them to the callback as third parameter
  // (and also as state parameter when no other state is present).
  function ancestor(node, visitors, base, state) {
    if (!base) base = exports.base
    var ancestors = []
    ;(function c(node, st, override) {
      var type = override || node.type, found = visitors[type]
      var isNew = node != ancestors[ancestors.length - 1]
      if (isNew) ancestors.push(node)
      base[type](node, st, c)
      if (found) found(node, st || ancestors, ancestors)
      if (isNew) ancestors.pop()
    })(node, state)
  }

  // A recursive walk is one where your functions override the default
  // walkers. They can modify and replace the state parameter that's
  // threaded through the walk, and can opt how and whether to walk
  // their child nodes (by calling their third argument on these
  // nodes).
  function recursive(node, state, funcs, base, override) {
    var visitor = funcs ? exports.make(funcs, base) : base
    ;(function c(node, st, override) {
      visitor[override || node.type](node, st, c)
    })(node, state, override)
  }

  function makeTest(test) {
    if (typeof test == "string")
      return function (type) { return type == test; }
    else if (!test)
      return function () { return true; }
    else
      return test
  }

  var Found = function Found(node, state) { this.node = node; this.state = state };

  // Find a node with a given start, end, and type (all are optional,
  // null can be used as wildcard). Returns a {node, state} object, or
  // undefined when it doesn't find a matching node.
  function findNodeAt(node, start, end, test, base, state) {
    test = makeTest(test)
    if (!base) base = exports.base
    try {
      ;(function c(node, st, override) {
        var type = override || node.type
        if ((start == null || node.start <= start) &&
            (end == null || node.end >= end))
          base[type](node, st, c)
        if ((start == null || node.start == start) &&
            (end == null || node.end == end) &&
            test(type, node))
          throw new Found(node, st)
      })(node, state)
    } catch (e) {
      if (e instanceof Found) return e
      throw e
    }
  }

  // Find the innermost node of a given type that contains the given
  // position. Interface similar to findNodeAt.
  function findNodeAround(node, pos, test, base, state) {
    test = makeTest(test)
    if (!base) base = exports.base
    try {
      ;(function c(node, st, override) {
        var type = override || node.type
        if (node.start > pos || node.end < pos) return
        base[type](node, st, c)
        if (test(type, node)) throw new Found(node, st)
      })(node, state)
    } catch (e) {
      if (e instanceof Found) return e
      throw e
    }
  }

  // Find the outermost matching node after a given position.
  function findNodeAfter(node, pos, test, base, state) {
    test = makeTest(test)
    if (!base) base = exports.base
    try {
      ;(function c(node, st, override) {
        if (node.end < pos) return
        var type = override || node.type
        if (node.start >= pos && test(type, node)) throw new Found(node, st)
        base[type](node, st, c)
      })(node, state)
    } catch (e) {
      if (e instanceof Found) return e
      throw e
    }
  }

  // Find the outermost matching node before a given position.
  function findNodeBefore(node, pos, test, base, state) {
    test = makeTest(test)
    if (!base) base = exports.base
    var max
    ;(function c(node, st, override) {
      if (node.start > pos) return
      var type = override || node.type
      if (node.end <= pos && (!max || max.node.end < node.end) && test(type, node))
        max = new Found(node, st)
      base[type](node, st, c)
    })(node, state)
    return max
  }

  // Fallback to an Object.create polyfill for older environments.
  var create = Object.create || function(proto) {
    function Ctor() {}
    Ctor.prototype = proto
    return new Ctor
  }

  // Used to create a custom walker. Will fill in all missing node
  // type properties with the defaults.
  function make(funcs, base) {
    if (!base) base = exports.base
    var visitor = create(base)
    for (var type in funcs) visitor[type] = funcs[type]
    return visitor
  }

  function skipThrough(node, st, c) { c(node, st) }
  function ignore(_node, _st, _c) {}

  // Node walkers.

  var base = {}

  base.Program = base.BlockStatement = function (node, st, c) {
    for (var i = 0; i < node.body.length; ++i)
      c(node.body[i], st, "Statement")
  }
  base.Statement = skipThrough
  base.EmptyStatement = ignore
  base.ExpressionStatement = base.ParenthesizedExpression =
    function (node, st, c) { return c(node.expression, st, "Expression"); }
  base.IfStatement = function (node, st, c) {
    c(node.test, st, "Expression")
    c(node.consequent, st, "Statement")
    if (node.alternate) c(node.alternate, st, "Statement")
  }
  base.LabeledStatement = function (node, st, c) { return c(node.body, st, "Statement"); }
  base.BreakStatement = base.ContinueStatement = ignore
  base.WithStatement = function (node, st, c) {
    c(node.object, st, "Expression")
    c(node.body, st, "Statement")
  }
  base.SwitchStatement = function (node, st, c) {
    c(node.discriminant, st, "Expression")
    for (var i = 0; i < node.cases.length; ++i) {
      var cs = node.cases[i]
      if (cs.test) c(cs.test, st, "Expression")
      for (var j = 0; j < cs.consequent.length; ++j)
        c(cs.consequent[j], st, "Statement")
    }
  }
  base.ReturnStatement = base.YieldExpression = base.AwaitExpression = function (node, st, c) {
    if (node.argument) c(node.argument, st, "Expression")
  }
  base.ThrowStatement = base.SpreadElement =
    function (node, st, c) { return c(node.argument, st, "Expression"); }
  base.TryStatement = function (node, st, c) {
    c(node.block, st, "Statement")
    if (node.handler) c(node.handler, st)
    if (node.finalizer) c(node.finalizer, st, "Statement")
  }
  base.CatchClause = function (node, st, c) {
    c(node.param, st, "Pattern")
    c(node.body, st, "ScopeBody")
  }
  base.WhileStatement = base.DoWhileStatement = function (node, st, c) {
    c(node.test, st, "Expression")
    c(node.body, st, "Statement")
  }
  base.ForStatement = function (node, st, c) {
    if (node.init) c(node.init, st, "ForInit")
    if (node.test) c(node.test, st, "Expression")
    if (node.update) c(node.update, st, "Expression")
    c(node.body, st, "Statement")
  }
  base.ForInStatement = base.ForOfStatement = function (node, st, c) {
    c(node.left, st, "ForInit")
    c(node.right, st, "Expression")
    c(node.body, st, "Statement")
  }
  base.ForInit = function (node, st, c) {
    if (node.type == "VariableDeclaration") c(node, st)
    else c(node, st, "Expression")
  }
  base.DebuggerStatement = ignore

  base.FunctionDeclaration = function (node, st, c) { return c(node, st, "Function"); }
  base.VariableDeclaration = function (node, st, c) {
    for (var i = 0; i < node.declarations.length; ++i)
      c(node.declarations[i], st)
  }
  base.VariableDeclarator = function (node, st, c) {
    c(node.id, st, "Pattern")
    if (node.init) c(node.init, st, "Expression")
  }

  base.Function = function (node, st, c) {
    if (node.id) c(node.id, st, "Pattern")
    for (var i = 0; i < node.params.length; i++)
      c(node.params[i], st, "Pattern")
    c(node.body, st, node.expression ? "ScopeExpression" : "ScopeBody")
  }
  // FIXME drop these node types in next major version
  // (They are awkward, and in ES6 every block can be a scope.)
  base.ScopeBody = function (node, st, c) { return c(node, st, "Statement"); }
  base.ScopeExpression = function (node, st, c) { return c(node, st, "Expression"); }

  base.Pattern = function (node, st, c) {
    if (node.type == "Identifier")
      c(node, st, "VariablePattern")
    else if (node.type == "MemberExpression")
      c(node, st, "MemberPattern")
    else
      c(node, st)
  }
  base.VariablePattern = ignore
  base.MemberPattern = skipThrough
  base.RestElement = function (node, st, c) { return c(node.argument, st, "Pattern"); }
  base.ArrayPattern =  function (node, st, c) {
    for (var i = 0; i < node.elements.length; ++i) {
      var elt = node.elements[i]
      if (elt) c(elt, st, "Pattern")
    }
  }
  base.ObjectPattern = function (node, st, c) {
    for (var i = 0; i < node.properties.length; ++i)
      c(node.properties[i].value, st, "Pattern")
  }

  base.Expression = skipThrough
  base.ThisExpression = base.Super = base.MetaProperty = ignore
  base.ArrayExpression = function (node, st, c) {
    for (var i = 0; i < node.elements.length; ++i) {
      var elt = node.elements[i]
      if (elt) c(elt, st, "Expression")
    }
  }
  base.ObjectExpression = function (node, st, c) {
    for (var i = 0; i < node.properties.length; ++i)
      c(node.properties[i], st)
  }
  base.FunctionExpression = base.ArrowFunctionExpression = base.FunctionDeclaration
  base.SequenceExpression = base.TemplateLiteral = function (node, st, c) {
    for (var i = 0; i < node.expressions.length; ++i)
      c(node.expressions[i], st, "Expression")
  }
  base.UnaryExpression = base.UpdateExpression = function (node, st, c) {
    c(node.argument, st, "Expression")
  }
  base.BinaryExpression = base.LogicalExpression = function (node, st, c) {
    c(node.left, st, "Expression")
    c(node.right, st, "Expression")
  }
  base.AssignmentExpression = base.AssignmentPattern = function (node, st, c) {
    c(node.left, st, "Pattern")
    c(node.right, st, "Expression")
  }
  base.ConditionalExpression = function (node, st, c) {
    c(node.test, st, "Expression")
    c(node.consequent, st, "Expression")
    c(node.alternate, st, "Expression")
  }
  base.NewExpression = base.CallExpression = function (node, st, c) {
    c(node.callee, st, "Expression")
    if (node.arguments) for (var i = 0; i < node.arguments.length; ++i)
      c(node.arguments[i], st, "Expression")
  }
  base.MemberExpression = function (node, st, c) {
    c(node.object, st, "Expression")
    if (node.computed) c(node.property, st, "Expression")
  }
  base.ExportNamedDeclaration = base.ExportDefaultDeclaration = function (node, st, c) {
    if (node.declaration)
      c(node.declaration, st, node.type == "ExportNamedDeclaration" || node.declaration.id ? "Statement" : "Expression")
    if (node.source) c(node.source, st, "Expression")
  }
  base.ExportAllDeclaration = function (node, st, c) {
    c(node.source, st, "Expression")
  }
  base.ImportDeclaration = function (node, st, c) {
    for (var i = 0; i < node.specifiers.length; i++)
      c(node.specifiers[i], st)
    c(node.source, st, "Expression")
  }
  base.ImportSpecifier = base.ImportDefaultSpecifier = base.ImportNamespaceSpecifier = base.Identifier = base.Literal = ignore

  base.TaggedTemplateExpression = function (node, st, c) {
    c(node.tag, st, "Expression")
    c(node.quasi, st)
  }
  base.ClassDeclaration = base.ClassExpression = function (node, st, c) { return c(node, st, "Class"); }
  base.Class = function (node, st, c) {
    if (node.id) c(node.id, st, "Pattern")
    if (node.superClass) c(node.superClass, st, "Expression")
    for (var i = 0; i < node.body.body.length; i++)
      c(node.body.body[i], st)
  }
  base.MethodDefinition = base.Property = function (node, st, c) {
    if (node.computed) c(node.key, st, "Expression")
    c(node.value, st, "Expression")
  }

  exports.simple = simple;
  exports.ancestor = ancestor;
  exports.recursive = recursive;
  exports.findNodeAt = findNodeAt;
  exports.findNodeAround = findNodeAround;
  exports.findNodeAfter = findNodeAfter;
  exports.findNodeBefore = findNodeBefore;
  exports.make = make;
  exports.base = base;

  Object.defineProperty(exports, '__esModule', { value: true });

}));