text: // 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 and
  // Statement, 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.
  
  export function simple(node, visitors, baseVisitor, state, override) {
    if (!baseVisitor) baseVisitor = base
    ;(function c(node, st, override) {
      let type = override || node.type, found = visitors[type]
      baseVisitor[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).
  export function ancestor(node, visitors, baseVisitor, state, override) {
    let ancestors = []
    if (!baseVisitor) baseVisitor = base
    ;(function c(node, st, override) {
      let type = override || node.type, found = visitors[type]
      let isNew = node !== ancestors[ancestors.length - 1]
      if (isNew) ancestors.push(node)
      baseVisitor[type](node, st, c)
      if (found) found(node, st || ancestors, ancestors)
      if (isNew) ancestors.pop()
    })(node, state, override)
  }
  
  // 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).
  export function recursive(node, state, funcs, baseVisitor, override) {
    let visitor = funcs ? make(funcs, baseVisitor || undefined) : baseVisitor
    ;(function c(node, st, override) {
      visitor[override || node.type](node, st, c)
    })(node, state, override)
  }
  
  function makeTest(test) {
    if (typeof test === "string")
      return type => type === test
    else if (!test)
      return () => true
    else
      return test
  }
  
  class Found {
    constructor(node, state) { this.node = node; this.state = state }
  }
  
  // A full walk triggers the callback on each node
  export function full(node, callback, baseVisitor, state, override) {
    if (!baseVisitor) baseVisitor = base
    ;(function c(node, st, override) {
      let type = override || node.type
      baseVisitor[type](node, st, c)
      if (!override) callback(node, st, type)
    })(node, state, override)
  }
  
  // An fullAncestor walk is like an ancestor walk, but triggers
  // the callback on each node
  export function fullAncestor(node, callback, baseVisitor, state) {
    if (!baseVisitor) baseVisitor = base
    let ancestors = []
    ;(function c(node, st, override) {
      let type = override || node.type
      let isNew = node !== ancestors[ancestors.length - 1]
      if (isNew) ancestors.push(node)
      baseVisitor[type](node, st, c)
      if (!override) callback(node, st || ancestors, ancestors, type)
      if (isNew) ancestors.pop()
    })(node, 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.
  export function findNodeAt(node, start, end, test, baseVisitor, state) {
    if (!baseVisitor) baseVisitor = base
    test = makeTest(test)
    try {
      (function c(node, st, override) {
        let type = override || node.type
        if ((start == null || node.start <= start) &&
            (end == null || node.end >= end))
          baseVisitor[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.
  export function findNodeAround(node, pos, test, baseVisitor, state) {
    test = makeTest(test)
    if (!baseVisitor) baseVisitor = base
    try {
      (function c(node, st, override) {
        let type = override || node.type
        if (node.start > pos || node.end < pos) return
        baseVisitor[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.
  export function findNodeAfter(node, pos, test, baseVisitor, state) {
    test = makeTest(test)
    if (!baseVisitor) baseVisitor = base
    try {
      (function c(node, st, override) {
        if (node.end < pos) return
        let type = override || node.type
        if (node.start >= pos && test(type, node)) throw new Found(node, st)
        baseVisitor[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.
  export function findNodeBefore(node, pos, test, baseVisitor, state) {
    test = makeTest(test)
    if (!baseVisitor) baseVisitor = base
    let max
    ;(function c(node, st, override) {
      if (node.start > pos) return
      let type = override || node.type
      if (node.end <= pos && (!max || max.node.end < node.end) && test(type, node))
        max = new Found(node, st)
      baseVisitor[type](node, st, c)
    })(node, state)
    return max
  }
  
  // Fallback to an Object.create polyfill for older environments.
  const 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.
  export function make(funcs, baseVisitor) {
    let visitor = create(baseVisitor || base)
    for (let type in funcs) visitor[type] = funcs[type]
    return visitor
  }
  
  function skipThrough(node, st, c) { c(node, st) }
  function ignore(_node, _st, _c) {}
  
  // Node walkers.
  
  export const base = {}
  
  base.Program = base.BlockStatement = (node, st, c) => {
    for (let stmt of node.body)
      c(stmt, st, "Statement")
  }
  base.Statement = skipThrough
  base.EmptyStatement = ignore
  base.ExpressionStatement = base.ParenthesizedExpression = base.ChainExpression =
    (node, st, c) => c(node.expression, st, "Expression")
  base.IfStatement = (node, st, c) => {
    c(node.test, st, "Expression")
    c(node.consequent, st, "Statement")
    if (node.alternate) c(node.alternate, st, "Statement")
  }
  base.LabeledStatement = (node, st, c) => c(node.body, st, "Statement")
  base.BreakStatement = base.ContinueStatement = ignore
  base.WithStatement = (node, st, c) => {
    c(node.object, st, "Expression")
    c(node.body, st, "Statement")
  }
  base.SwitchStatement = (node, st, c) => {
    c(node.discriminant, st, "Expression")
    for (let cs of node.cases) {
      if (cs.test) c(cs.test, st, "Expression")
      for (let cons of cs.consequent)
        c(cons, st, "Statement")
    }
  }
  base.SwitchCase = (node, st, c) => {
    if (node.test) c(node.test, st, "Expression")
    for (let cons of node.consequent)
      c(cons, st, "Statement")
  }
  base.ReturnStatement = base.YieldExpression = base.AwaitExpression = (node, st, c) => {
    if (node.argument) c(node.argument, st, "Expression")
  }
  base.ThrowStatement = base.SpreadElement =
    (node, st, c) => c(node.argument, st, "Expression")
  base.TryStatement = (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 = (node, st, c) => {
    if (node.param) c(node.param, st, "Pattern")
    c(node.body, st, "Statement")
  }
  base.WhileStatement = base.DoWhileStatement = (node, st, c) => {
    c(node.test, st, "Expression")
    c(node.body, st, "Statement")
  }
  base.ForStatement = (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 = (node, st, c) => {
    c(node.left, st, "ForInit")
    c(node.right, st, "Expression")
    c(node.body, st, "Statement")
  }
  base.ForInit = (node, st, c) => {
    if (node.type === "VariableDeclaration") c(node, st)
    else c(node, st, "Expression")
  }
  base.DebuggerStatement = ignore
  
  base.FunctionDeclaration = (node, st, c) => c(node, st, "Function")
  base.VariableDeclaration = (node, st, c) => {
    for (let decl of node.declarations)
      c(decl, st)
  }
  base.VariableDeclarator = (node, st, c) => {
    c(node.id, st, "Pattern")
    if (node.init) c(node.init, st, "Expression")
  }
  
  base.Function = (node, st, c) => {
    if (node.id) c(node.id, st, "Pattern")
    for (let param of node.params)
      c(param, st, "Pattern")
    c(node.body, st, node.expression ? "Expression" : "Statement")
  }
  
  base.Pattern = (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 = (node, st, c) => c(node.argument, st, "Pattern")
  base.ArrayPattern = (node, st, c) => {
    for (let elt of node.elements) {
      if (elt) c(elt, st, "Pattern")
    }
  }
  base.ObjectPattern = (node, st, c) => {
    for (let prop of node.properties) {
      if (prop.type === "Property") {
        if (prop.computed) c(prop.key, st, "Expression")
        c(prop.value, st, "Pattern")
      } else if (prop.type === "RestElement") {
        c(prop.argument, st, "Pattern")
      }
    }
  }
  
  base.Expression = skipThrough
  base.ThisExpression = base.Super = base.MetaProperty = ignore
  base.ArrayExpression = (node, st, c) => {
    for (let elt of node.elements) {
      if (elt) c(elt, st, "Expression")
    }
  }
  base.ObjectExpression = (node, st, c) => {
    for (let prop of node.properties)
      c(prop, st)
  }
  base.FunctionExpression = base.ArrowFunctionExpression = base.FunctionDeclaration
  base.SequenceExpression = (node, st, c) => {
    for (let expr of node.expressions)
      c(expr, st, "Expression")
  }
  base.TemplateLiteral = (node, st, c) => {
    for (let quasi of node.quasis)
      c(quasi, st)
  
    for (let expr of node.expressions)
      c(expr, st, "Expression")
  }
  base.TemplateElement = ignore
  base.UnaryExpression = base.UpdateExpression = (node, st, c) => {
    c(node.argument, st, "Expression")
  }
  base.BinaryExpression = base.LogicalExpression = (node, st, c) => {
    c(node.left, st, "Expression")
    c(node.right, st, "Expression")
  }
  base.AssignmentExpression = base.AssignmentPattern = (node, st, c) => {
    c(node.left, st, "Pattern")
    c(node.right, st, "Expression")
  }
  base.ConditionalExpression = (node, st, c) => {
    c(node.test, st, "Expression")
    c(node.consequent, st, "Expression")
    c(node.alternate, st, "Expression")
  }
  base.NewExpression = base.CallExpression = (node, st, c) => {
    c(node.callee, st, "Expression")
    if (node.arguments)
      for (let arg of node.arguments)
        c(arg, st, "Expression")
  }
  base.MemberExpression = (node, st, c) => {
    c(node.object, st, "Expression")
    if (node.computed) c(node.property, st, "Expression")
  }
  base.ExportNamedDeclaration = base.ExportDefaultDeclaration = (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 = (node, st, c) => {
    if (node.exported)
      c(node.exported, st)
    c(node.source, st, "Expression")
  }
  base.ImportDeclaration = (node, st, c) => {
    for (let spec of node.specifiers)
      c(spec, st)
    c(node.source, st, "Expression")
  }
  base.ImportExpression = (node, st, c) => {
    c(node.source, st, "Expression")
  }
  base.ImportSpecifier = base.ImportDefaultSpecifier = base.ImportNamespaceSpecifier = base.Identifier = base.Literal = ignore
  
  base.TaggedTemplateExpression = (node, st, c) => {
    c(node.tag, st, "Expression")
    c(node.quasi, st, "Expression")
  }
  base.ClassDeclaration = base.ClassExpression = (node, st, c) => c(node, st, "Class")
  base.Class = (node, st, c) => {
    if (node.id) c(node.id, st, "Pattern")
    if (node.superClass) c(node.superClass, st, "Expression")
    c(node.body, st)
  }
  base.ClassBody = (node, st, c) => {
    for (let elt of node.body)
      c(elt, st)
  }
  base.MethodDefinition = base.Property = (node, st, c) => {
    if (node.computed) c(node.key, st, "Expression")
    c(node.value, st, "Expression")
  }
  