Golang Lexer.Backup方法代碼示例

func lexInside(l *lex.Lexer) lex.StateFn {
	for {
		switch r := l.Next(); {
		case r == rightCurl:
			l.Depth -= 1
			l.Emit(itemRightCurl)
			if l.Depth == 0 {
				return lexText
			}
		case r == leftCurl:
			l.Depth += 1
			l.Emit(itemLeftCurl)
		case r == lex.EOF:
			return l.Errorf("unclosed action")
		case isSpace(r) || isEndOfLine(r) || r == ',':
			l.Ignore()
		case isNameBegin(r):
			return lexName
		case r == '#':
			l.Backup()
			return lexComment
		case r == '(':
			l.Emit(itemLeftRound)
			return lexArgInside
		default:
			return l.Errorf("Unrecognized character in lexInside: %#U", r)
		}
	}
}

// lexDirective is called right after we see a @.
func lexDirective(l *lex.Lexer) lex.StateFn {
	r := l.Next()
	if !isNameBegin(r) {
		return l.Errorf("Unrecognized character in lexDirective: %#U", r)
	}

	l.Backup()
	// This gives our buffer an initial capacity. Its length is zero though. The
	// buffer can grow beyond this initial capacity.
	buf := bytes.NewBuffer(make([]byte, 0, 15))
	for {
		// The caller already checked isNameBegin, and absorbed one rune.
		r = l.Next()
		buf.WriteRune(r)
		if isNameSuffix(r) {
			continue
		}
		l.Backup()
		l.Emit(itemDirectiveName)

		directive := buf.Bytes()[:buf.Len()-1]
		// The lexer may behave differently for different directives. Hence, we need
		// to check the directive here and go into the right state.
		if string(directive) == "filter" {
			return lexFilterInside
		}
		return l.Errorf("Unhandled directive %s", directive)
	}
	return lexInside
}

// This function inspects the next rune and calls the appropriate stateFn.
func lexText(l *lex.Lexer) lex.StateFn {
Loop:
	for {
		switch r := l.Next(); {
		case r == '<' || r == '_':
			if l.Depth == atSubject {
				l.Backup()
				l.Emit(itemText) // emit whatever we have so far.
				return lexSubject
			}

			if l.Depth == atPredicate {
				l.Backup()
				l.Emit(itemText)
				return lexPredicate
			}

			if l.Depth == atObject {
				l.Backup()
				l.Emit(itemText)
				return lexObject
			}

			if l.Depth == atLabel {
				l.Backup()
				l.Emit(itemText)
				return lexLabel
			}

			return l.Errorf("Invalid input: %c at lexText", r)

		case r == '"':
			if l.Depth != atObject {
				return l.Errorf("Invalid quote for non-object.")
			}
			l.Backup()
			l.Emit(itemText)
			return lexObject

		case r == lex.EOF:
			break Loop

		case r == '.':
			if l.Depth > atObject {
				l.Emit(itemValidEnd)
			}
			break Loop

		case isSpace(r):
			continue
		default:
			l.Errorf("Invalid input: %c at lexText", r)
		}
	}
	if l.Pos > l.Start {
		l.Emit(itemText)
	}
	l.Emit(lex.ItemEOF)
	return nil
}

func lexObject(l *lex.Lexer) lex.StateFn {
	for {
		switch r := l.Next(); {
		case r == rightCurl:
			return lexText
		case isSpace(r) || isEndOfLine(r):
			l.Ignore()
		case isNameBegin(r):
			{
				for {
					r := l.Next()
					if isNameSuffix(r) {
						continue // absorb
					}
					l.Backup()
					l.Emit(itemObject)
					break
				}
				return lexObjectBlock
			}
		default:
			return l.Errorf("Invalid schema. Unexpected %s", l.Input[l.Start:l.Pos])
		}
	}
}

// Assumes '"' has already been encountered.
func lexLiteral(l *lex.Lexer) lex.StateFn {
	for {
		r := l.Next()
		if r == '\u005c' { // backslash
			r = l.Next()
			continue // This would skip over the escaped rune.
		}

		if r == lex.EOF || isEndLiteral(r) {
			break
		}
	}
	l.Backup()

	l.Emit(itemLiteral)
	l.Next()   // Move to end literal.
	l.Ignore() // Ignore end literal.
	l.Depth++

	r := l.Peek()
	if r == '@' {
		return lexLanguage(l)
	}

	if r == '^' {
		return lexObjectType(l)
	}

	return lexText
}

// lexTextMutation lexes and absorbs the text inside a mutation operation block.
func lexTextMutation(l *lex.Lexer) lex.StateFn {
	for {
		r := l.Next()
		if r == lex.EOF {
			return l.Errorf("Unclosed mutation text")
		}
		if r == quote {
			return lexMutationValue
		}
		if r == leftCurl {
			l.Depth++
		}
		if r == rightCurl {
			if l.Depth > 2 {
				l.Depth--
				continue
			}
		}
		if r != rightCurl {
			// Absorb everything until we find '}'.
			continue
		}
		l.Backup()
		l.Emit(itemMutationContent)
		break
	}
	return lexInsideMutation
}

// lexOperationType lexes a query or mutation operation type.
func lexOperationType(l *lex.Lexer) lex.StateFn {
	for {
		r := l.Next()
		if isNameSuffix(r) {
			continue // absorb
		}
		l.Backup()
		// l.Pos would be index of the end of operation type + 1.
		word := l.Input[l.Start:l.Pos]
		if word == "mutation" {
			l.Emit(itemOpType)
			l.Mode = mutationMode
		} else if word == "fragment" {
			l.Emit(itemOpType)
			l.Mode = fragmentMode
		} else if word == "query" {
			l.Emit(itemOpType)
			l.Mode = queryMode
		} else {
			if l.Mode == 0 {
				l.Errorf("Invalid operation type")
			}
		}
		break
	}
	return lexText
}

func lexText(l *lex.Lexer) lex.StateFn {
Loop:
	for {
		switch r := l.Next(); {
		case r == leftCurl:
			l.Backup()
			l.Emit(itemText) // emit whatever we have so far.
			l.Next()         // advance one to get back to where we saw leftCurl.
			l.Depth += 1     // one level down.
			l.Emit(itemLeftCurl)
			return lexInside // we're in.

		case r == rightCurl:
			return l.Errorf("Too many right characters")
		case r == lex.EOF:
			break Loop
		case isNameBegin(r):
			l.Backup()
			l.Emit(itemText)
			return lexOperationType
		}
	}
	if l.Pos > l.Start {
		l.Emit(itemText)
	}
	l.Emit(lex.ItemEOF)
	return nil
}

func lexFragmentSpread(l *lex.Lexer) lex.StateFn {
	for {
		r := l.Next()
		if isNameSuffix(r) {
			continue
		}
		l.Backup()
		l.Emit(itemFragmentSpread)
		break
	}
	return lexInside
}

// lexArgName lexes and emits the name part of an argument.
func lexArgName(l *lex.Lexer) lex.StateFn {
	for {
		r := l.Next()
		if isNameSuffix(r) {
			continue
		}
		l.Backup()
		l.Emit(itemArgName)
		break
	}
	return lexArgInside
}

// lexNameMutation lexes the itemMutationOp, which could be set or delete.
func lexNameMutation(l *lex.Lexer) lex.StateFn {
	for {
		// The caller already checked isNameBegin, and absorbed one rune.
		r := l.Next()
		if isNameBegin(r) {
			continue
		}
		l.Backup()
		l.Emit(itemMutationOp)
		break
	}
	return lexInsideMutation
}

// lexFilterFuncName expects input to look like equal("...", "...").
func lexFilterFuncName(l *lex.Lexer) lex.StateFn {
	for {
		// The caller already checked isNameBegin, and absorbed one rune.
		r := l.Next()
		if isNameSuffix(r) {
			continue
		}
		l.Backup()
		l.Emit(itemFilterFunc)
		break
	}
	return lexFilterFuncInside
}

func lexAlias(l *lex.Lexer) lex.StateFn {
	l.AcceptRun(isSpace)
	l.Ignore() // Any spaces encountered.
	for {
		r := l.Next()
		if isNameSuffix(r) {
			continue
		}
		l.Backup()
		l.Emit(itemAlias)
		break
	}
	return lexInside
}

func lexOperationType(l *lex.Lexer) lex.StateFn {
	for {
		r := l.Next()
		if isNameSuffix(r) {
			continue // absorb
		}
		l.Backup()
		word := l.Input[l.Start:l.Pos]
		if word == "query" || word == "mutation" {
			l.Emit(itemOpType)
		}
		break
	}
	return lexText
}

func lexScalarBlock(l *lex.Lexer) lex.StateFn {
	for {
		switch r := l.Next(); {
		case r == ')':
			l.Emit(itemRightRound)
			return lexText
		case isNameBegin(r):
			l.Backup()
			return lexScalarPair1
		case isSpace(r) || isEndOfLine(r):
			l.Ignore()
		default:
			return l.Errorf("Invalid schema. Unexpected %s", l.Input[l.Start:l.Pos])
		}
	}
}