Documentation
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Overview ¶
Tokenize UTF-8-encoded Prolog text. It takes an io.Reader providing the source, which then can be tokenized with the Scan function. For compatibility with existing tools, the NUL character is not allowed. If the first character in the source is a UTF-8 encoded byte order mark (BOM), it is discarded.
Basic usage pattern:
lexemes := lex.Scan(file)
for lexeme := range lexemes {
// do something with lexeme
}
Index ¶
Constants ¶
const ( EOF = -(iota + 1) // reached end of source Atom // a Prolog atom, possibly quoted Comment // a comment Float // a floating point number Functor // an atom used as a predicate functor FullStop // "." ending a term Int // an integer String // a double-quoted string Variable // a Prolog variable Void // the special "_" variable )
The result of Scan is one of these tokens or a Unicode character.
Variables ¶
This section is empty.
Functions ¶
func Scan ¶
Scan tokenizes src in a separate goroutine sending lexemes down a channel as they become available. The channel is closed on EOF.
func TokenString ¶
TokenString returns a printable string for a token or Unicode character.
Types ¶
type List ¶
type List struct {
Value *Eme
// contains filtered or unexported fields
}
An immutable list of lexemes which populates its tail by reading lexemes from a channel, such as that provided by Scan()
type Position ¶
type Position struct {
Filename string // filename, if any
Offset int // byte offset, starting at 0
Line int // line number, starting at 1
Column int // column number, starting at 1 (character count per line)
}
A source position is represented by a Position value. A position is valid if Line > 0.
type Scanner ¶
type Scanner struct {
// Error is called for each error encountered. If no Error
// function is set, the error is reported to os.Stderr.
Error func(s *Scanner, msg string)
// ErrorCount is incremented by one for each error encountered.
ErrorCount int
// Start position of most recently scanned token; set by Scan.
// Calling Init or Next invalidates the position (Line == 0).
// The Filename field is always left untouched by the Scanner.
// If an error is reported (via Error) and Position is invalid,
// the scanner is not inside a token. Call Pos to obtain an error
// position in that case.
Position
// contains filtered or unexported fields
}
A Scanner implements reading of Unicode characters and tokens from an io.Reader.
func (*Scanner) Init ¶
Init initializes a Scanner with a new source and returns s. Error is set to nil, ErrorCount is set to 0
func (*Scanner) Next ¶
Next reads and returns the next Unicode character. It returns EOF at the end of the source. It reports a read error by calling s.Error, if not nil; otherwise it prints an error message to os.Stderr. Next does not update the Scanner's Position field; use Pos() to get the current position.
func (*Scanner) Peek ¶
Peek returns the next Unicode character in the source without advancing the scanner. It returns EOF if the scanner's position is at the last character of the source.
func (*Scanner) Pos ¶
Pos returns the position of the character immediately after the character or token returned by the last call to Next or Scan.
Source Files