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| package calculator
|
| import (
| "errors"
| "fmt"
| "strings"
| )
|
| const (
| Identifier = iota
| // e.g. 50
| Literal
| // e.g. + - * /
| Operator
| // ,
| COMMA
| )
|
| type Token struct {
| // raw characters
| Tok string
| // type with Literal/Operator
| Type,
| Flag int
|
| Offset int
| }
|
| type Parser struct {
| Source string
|
| ch byte
| offset int
|
| err error
| }
|
| func Parse(s string) ([]*Token, error) {
| p := &Parser{
| Source: s,
| err: nil,
| ch: s[0],
| }
| toks := p.parse()
| if p.err != nil {
| return nil, p.err
| }
| return toks, nil
| }
|
| func (p *Parser) parse() []*Token {
| toks := make([]*Token, 0)
| for {
| tok := p.nextTok()
| if tok == nil {
| break
| }
| toks = append(toks, tok)
| }
| return toks
| }
|
| func (p *Parser) nextTok() *Token {
| if p.offset >= len(p.Source) || p.err != nil {
| return nil
| }
| var err error
| for p.isWhitespace(p.ch) && err == nil {
| err = p.nextCh()
| }
| start := p.offset
| var tok *Token
| switch p.ch {
| case
| '(',
| ')',
| '+',
| '-',
| '*',
| '/',
| '^',
| '%':
| tok = &Token{
| Tok: string(p.ch),
| Type: Operator,
| }
| tok.Offset = start
| err = p.nextCh()
|
| case
| '0',
| '1',
| '2',
| '3',
| '4',
| '5',
| '6',
| '7',
| '8',
| '9':
| for p.isDigitNum(p.ch) && p.nextCh() == nil {
| if (p.ch == '-' || p.ch == '+') && p.Source[p.offset-1] != 'e' {
| break
| }
| }
| tok = &Token{
| Tok: strings.ReplaceAll(p.Source[start:p.offset], "_", ""),
| Type: Literal,
| }
| tok.Offset = start
|
| case ',':
| tok = &Token{
| Tok: string(p.ch),
| Type: COMMA,
| }
| tok.Offset = start
| err = p.nextCh()
|
| default:
| if p.isChar(p.ch) {
| for p.isWordChar(p.ch) && p.nextCh() == nil {
| }
| tok = &Token{
| Tok: p.Source[start:p.offset],
| Type: Identifier,
| }
| tok.Offset = start
| } else if p.ch != ' ' {
| s := fmt.Sprintf("symbol error: unknown '%v', pos [%v:]\n%s",
| string(p.ch),
| start,
| ErrPos(p.Source, start))
| p.err = errors.New(s)
| }
| }
| return tok
| }
|
| func (p *Parser) nextCh() error {
| p.offset++
| if p.offset < len(p.Source) {
| p.ch = p.Source[p.offset]
| return nil
| }
| return errors.New("EOF")
| }
|
| func (p *Parser) isWhitespace(c byte) bool {
| return c == ' ' ||
| c == '\t' ||
| c == '\n' ||
| c == '\v' ||
| c == '\f' ||
| c == '\r'
| }
|
| func (p *Parser) isDigitNum(c byte) bool {
| return '0' <= c && c <= '9' || c == '.' || c == '_' || c == 'e' || c == '-' || c == '+'
| }
|
| func (p *Parser) isChar(c byte) bool {
| return 'a' <= c && c <= 'z' || 'A' <= c && c <= 'Z'
| }
|
| func (p *Parser) isWordChar(c byte) bool {
| return p.isChar(c) || '0' <= c && c <= '9'
| }
|
|
