parser/stack_machine.go

/*
This Source Code Form is subject to the terms of the Mozilla Public
License, v. 2.0. If a copy of the MPL was not distributed with this
file, You can obtain one at https://mozilla.org/MPL/2.0/.
*/

package parser

import (
	"errors"
	"fmt"
)

func NewUnrecognized(msg string, val rune) error {
	return &UnrecognizedInputError{msg: msg, val: val}
}

type UnrecognizedInputError struct {
	msg string
	val rune
}

func (e *UnrecognizedInputError) Error() string {
	return fmt.Sprintf("%s: unrecognized input: '%s'", e.msg, string(e.val))
}

func (e *UnrecognizedInputError) Unwrap() error {
	return e
}

type SM struct {
	stack     []*CSTNode
	line, col int
}

func (m *SM) Top() *CSTNode {
	return m.stack[len(m.stack)-1]
}

func (m *SM) Push(t ASTNode) ASTNode {
	m.stack = append(m.stack, &CSTNode{ASTNode: t})
	return t
}

func (m *SM) shift(e rune) (err error) {
	m.col++
	for {
		err = m.Top().ASTNode.Shift(m, e)
		if !errors.Is(err, &UnrecognizedInputError{}) {
			break
		}
		if !m.reduce() {
			break
		}
	}
	return err
}

func (m *SM) reduce() bool {
	if len(m.stack) < 2 {
		return false
	}
	last := len(m.stack) - 1

	nodes := m.stack[last-1].Nodes
	nodes = append(nodes, m.stack[last])
	m.stack[last-1].Nodes = nodes

	m.stack = m.stack[:last]
	return true
}