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// Copyright 2018 The CUE Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package ast
import (
"fmt"
)
func walkList[N Node](list []N, before func(Node) bool, after func(Node)) {
for _, node := range list {
Walk(node, before, after)
}
}
// Walk traverses an AST in depth-first order: It starts by calling f(node);
// node must not be nil. If before returns true, Walk invokes f recursively for
// each of the non-nil children of node, followed by a call of after. Both
// functions may be nil. If before is nil, it is assumed to always return true.
func Walk(node Node, before func(Node) bool, after func(Node)) {
if before != nil && !before(node) {
return
}
// TODO: record the comment groups and interleave with the values like for
// parsing and printing?
walkList(Comments(node), before, after)
// walk children
// (the order of the cases matches the order
// of the corresponding node types in go)
switch n := node.(type) {
// Comments and fields
case *Comment:
// nothing to do
case *CommentGroup:
walkList(n.List, before, after)
case *Attribute:
// nothing to do
case *Field:
Walk(n.Label, before, after)
if n.Value != nil {
Walk(n.Value, before, after)
}
walkList(n.Attrs, before, after)
case *Func:
walkList(n.Args, before, after)
Walk(n.Ret, before, after)
case *StructLit:
walkList(n.Elts, before, after)
// Expressions
case *BottomLit, *BadExpr, *Ident, *BasicLit:
// nothing to do
case *Interpolation:
walkList(n.Elts, before, after)
case *ListLit:
walkList(n.Elts, before, after)
case *Ellipsis:
if n.Type != nil {
Walk(n.Type, before, after)
}
case *ParenExpr:
Walk(n.X, before, after)
case *SelectorExpr:
Walk(n.X, before, after)
Walk(n.Sel, before, after)
case *IndexExpr:
Walk(n.X, before, after)
Walk(n.Index, before, after)
case *SliceExpr:
Walk(n.X, before, after)
if n.Low != nil {
Walk(n.Low, before, after)
}
if n.High != nil {
Walk(n.High, before, after)
}
case *CallExpr:
Walk(n.Fun, before, after)
walkList(n.Args, before, after)
case *UnaryExpr:
Walk(n.X, before, after)
case *BinaryExpr:
Walk(n.X, before, after)
Walk(n.Y, before, after)
// Declarations
case *ImportSpec:
if n.Name != nil {
Walk(n.Name, before, after)
}
Walk(n.Path, before, after)
case *BadDecl:
// nothing to do
case *ImportDecl:
walkList(n.Specs, before, after)
case *EmbedDecl:
Walk(n.Expr, before, after)
case *LetClause:
Walk(n.Ident, before, after)
Walk(n.Expr, before, after)
case *Alias:
Walk(n.Ident, before, after)
Walk(n.Expr, before, after)
case *Comprehension:
walkList(n.Clauses, before, after)
Walk(n.Value, before, after)
// Files and packages
case *File:
walkList(n.Decls, before, after)
case *Package:
Walk(n.Name, before, after)
case *ForClause:
if n.Key != nil {
Walk(n.Key, before, after)
}
Walk(n.Value, before, after)
Walk(n.Source, before, after)
case *IfClause:
Walk(n.Condition, before, after)
default:
panic(fmt.Sprintf("Walk: unexpected node type %T", n))
}
if after != nil {
after(node)
}
}
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