scanner

Documentation

Overview

Package scanner implements a scanner for CUE source text. It takes a []byte as source which can then be tokenized through repeated calls to the Scan method.

Index

• type ErrorHandler
• type Mode
• type Scanner
  • func (s *Scanner) Init(file *token.File, src []byte, eh ErrorHandler, mode Mode)
  • func (s *Scanner) Offset() int
  • func (s *Scanner) ResumeInterpolation() string
  • func (s *Scanner) Scan() (pos token.Pos, tok token.Token, lit string)

Types

type ErrorHandler

type ErrorHandler func(pos token.Pos, msg string, args []interface{})

An ErrorHandler is a generic error handler used throughout CUE packages.

The position points to the beginning of the offending value.

type Mode

type Mode uint

A Mode value is a set of flags (or 0). They control scanner behavior.

const (
	ScanComments     Mode = 1 << iota // return comments as COMMENT tokens
	DontInsertCommas                  // do not automatically insert commas
)

These constants are options to the Init function.

type Scanner

type Scanner struct {

	// public state - ok to modify
	ErrorCount int // number of errors encountered
	// contains filtered or unexported fields
}

A Scanner holds the Scanner's internal state while processing a given text. It can be allocated as part of another data structure but must be initialized via Init before use.

func (*Scanner) Init

func (s *Scanner) Init(file *token.File, src []byte, eh ErrorHandler, mode Mode)

Init prepares the scanner s to tokenize the text src by setting the scanner at the beginning of src. The scanner uses the file set file for position information and it adds line information for each line. It is ok to re-use the same file when re-scanning the same file as line information which is already present is ignored. Init causes a panic if the file size does not match the src size.

Calls to Scan will invoke the error handler err if they encounter a syntax error and err is not nil. Also, for each error encountered, the Scanner field ErrorCount is incremented by one. The mode parameter determines how comments are handled.

Note that Init may call err if there is an error in the first character of the file.

func (*Scanner) Offset

func (s *Scanner) Offset() int

Offset returns the current position offset.

func (*Scanner) ResumeInterpolation

func (s *Scanner) ResumeInterpolation() string

ResumeInterpolation resumes scanning of a string interpolation.

func (*Scanner) Scan

func (s *Scanner) Scan() (pos token.Pos, tok token.Token, lit string)

Scan scans the next token and returns the token position, the token, and its literal string if applicable. The source end is indicated by EOF.

If the returned token is a literal (IDENT, INT, FLOAT, IMAG, CHAR, STRING) or COMMENT, the literal string has the corresponding value.

If the returned token is a keyword, the literal string is the keyword.

If the returned token is Comma, the corresponding literal string is "," if the comma was present in the source, and "\n" if the semicolon was inserted because of a newline or at EOF.

If the returned token is ILLEGAL, the literal string is the offending character.

In all other cases, Scan returns an empty literal string.

For more tolerant parsing, Scan will return a valid token if possible even if a syntax error was encountered. Thus, even if the resulting token sequence contains no illegal tokens, a client may not assume that no error occurred. Instead it must check the scanner's ErrorCount or the number of calls of the error handler, if there was one installed.

Scan adds line information to the file added to the file set with Init. Token positions are relative to that file and thus relative to the file set.