fixed dependencies

vendor/github.com/go-latex/latex/ast/walk.go

@@ -0,0 +1,88 @@
+// Copyright ©2020 The go-latex Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package ast
+
+import "fmt"
+
+// A Visitor's Visit method is invoked for each node encountered by Walk.
+// If the result visitor w is not nil, Walk visits each of the children
+// of node with the visitor w, followed by a call of w.Visit(nil).
+type Visitor interface {
+	Visit(node Node) (w Visitor)
+}
+
+// Walk traverses an AST in depth-first order: It starts by calling
+// v.Visit(node); node must not be nil. If the visitor w returned by
+// v.Visit(node) is not nil, Walk is invoked recursively with visitor
+// w for each of the non-nil children of node, followed by a call of
+// w.Visit(nil).
+func Walk(v Visitor, node Node) {
+	if v = v.Visit(node); v == nil {
+		return
+	}
+
+	switch n := node.(type) {
+	case List:
+		for _, x := range n {
+			Walk(v, x)
+		}
+
+	case *Macro:
+		if n.Name != nil {
+			Walk(v, n.Name)
+		}
+		walkNodes(v, n.Args)
+
+	case *Arg:
+		walkNodes(v, n.List)
+
+	case *OptArg:
+		walkNodes(v, n.List)
+
+	case *Ident:
+		// nothing to do.
+
+	case *MathExpr:
+		walkNodes(v, n.List)
+
+	case *Word, *Literal, *Symbol:
+		// nothing to do.
+
+	case *Sub:
+		Walk(v, n.Node)
+
+	case *Sup:
+		Walk(v, n.Node)
+
+	default:
+		panic(fmt.Errorf("unknown ast node %#v (type=%T)", n, n))
+	}
+
+	v.Visit(nil)
+}
+
+func walkNodes(v Visitor, nodes []Node) {
+	for _, x := range nodes {
+		Walk(v, x)
+	}
+}
+
+type inspector func(Node) bool
+
+func (f inspector) Visit(node Node) Visitor {
+	if f(node) {
+		return f
+	}
+	return nil
+}
+
+// Inspect traverses an AST in depth-first order: It starts by calling
+// f(node); node must not be nil. If f returns true, Inspect invokes f
+// recursively for each of the non-nil children of node, followed by a
+// call of f(nil).
+//
+func Inspect(node Node, f func(Node) bool) {
+	Walk(inspector(f), node)
+}