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// Copyright (c) 2012-2017 The ANTLR Project. All rights reserved.
// Use of this file is governed by the BSD 3-clause license that
// can be found in the LICENSE.txt file in the project root.
package antlr
// A rule context is a record of a single rule invocation. It knows
// which context invoked it, if any. If there is no parent context, then
// naturally the invoking state is not valid. The parent link
// provides a chain upwards from the current rule invocation to the root
// of the invocation tree, forming a stack. We actually carry no
// information about the rule associated with b context (except
// when parsing). We keep only the state number of the invoking state from
// the ATN submachine that invoked b. Contrast b with the s
// pointer inside ParserRuleContext that tracks the current state
// being "executed" for the current rule.
// The parent contexts are useful for computing lookahead sets and
// getting error information.
// These objects are used during parsing and prediction.
// For the special case of parsers, we use the subclass
// ParserRuleContext.
// @see ParserRuleContext
type RuleContext interface {
GetInvokingState() int
GetRuleIndex() int
IsEmpty() bool
GetAltNumber() int
SetAltNumber(altNumber int)
String([]string, RuleContext) string
type BaseRuleContext struct {
parentCtx RuleContext
invokingState int
RuleIndex int
func NewBaseRuleContext(parent RuleContext, invokingState int) *BaseRuleContext {
rn := new(BaseRuleContext)
// What context invoked b rule?
rn.parentCtx = parent
// What state invoked the rule associated with b context?
// The "return address" is the followState of invokingState
// If parent is nil, b should be -1.
if parent == nil {
rn.invokingState = -1
} else {
rn.invokingState = invokingState
return rn
func (b *BaseRuleContext) GetBaseRuleContext() *BaseRuleContext {
return b
func (b *BaseRuleContext) SetParent(v Tree) {
if v == nil {
b.parentCtx = nil
} else {
b.parentCtx = v.(RuleContext)
func (b *BaseRuleContext) GetInvokingState() int {
return b.invokingState
func (b *BaseRuleContext) SetInvokingState(t int) {
b.invokingState = t
func (b *BaseRuleContext) GetRuleIndex() int {
return b.RuleIndex
func (b *BaseRuleContext) GetAltNumber() int {
return ATNInvalidAltNumber
func (b *BaseRuleContext) SetAltNumber(altNumber int) {}
// A context is empty if there is no invoking state meaning nobody call
// current context.
func (b *BaseRuleContext) IsEmpty() bool {
return b.invokingState == -1
// Return the combined text of all child nodes. This method only considers
// tokens which have been added to the parse tree.
// <p>
// Since tokens on hidden channels (e.g. whitespace or comments) are not
// added to the parse trees, they will not appear in the output of b
// method.
func (b *BaseRuleContext) GetParent() Tree {
return b.parentCtx
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