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package lexer
import (
"fmt"
"io"
)
const (
// EOF represents an end of file.
EOF rune = -(iota + 1)
)
// EOFToken creates a new EOF token at the given position.
func EOFToken(pos Position) Token {
return Token{Type: EOF, Pos: pos}
}
// Definition provides the parser with metadata for a lexer.
type Definition interface {
// Lex an io.Reader.
Lex(io.Reader) (Lexer, error)
// Symbols returns a map of symbolic names to the corresponding pseudo-runes for those symbols.
// This is the same approach as used by text/scanner. For example, "EOF" might have the rune
// value of -1, "Ident" might be -2, and so on.
Symbols() map[string]rune
}
// A Lexer returns tokens from a source.
type Lexer interface {
// Next consumes and returns the next token.
Next() (Token, error)
}
// SymbolsByRune returns a map of lexer symbol names keyed by rune.
func SymbolsByRune(def Definition) map[rune]string {
out := map[rune]string{}
for s, r := range def.Symbols() {
out[r] = s
}
return out
}
// NameOfReader attempts to retrieve the filename of a reader.
func NameOfReader(r interface{}) string {
if nr, ok := r.(interface{ Name() string }); ok {
return nr.Name()
}
return ""
}
// Must takes the result of a Definition constructor call and returns the definition, but panics if
// it errors
//
// eg.
//
// lex = lexer.Must(lexer.Build(`Symbol = "symbol" .`))
func Must(def Definition, err error) Definition {
if err != nil {
panic(err)
}
return def
}
// ConsumeAll reads all tokens from a Lexer.
func ConsumeAll(lexer Lexer) ([]Token, error) {
tokens := []Token{}
for {
token, err := lexer.Next()
if err != nil {
return nil, err
}
tokens = append(tokens, token)
if token.Type == EOF {
return tokens, nil
}
}
}
// Position of a token.
type Position struct {
Filename string
Offset int
Line int
Column int
}
func (p Position) GoString() string {
return fmt.Sprintf("Position{Filename: %q, Offset: %d, Line: %d, Column: %d}",
p.Filename, p.Offset, p.Line, p.Column)
}
func (p Position) String() string {
filename := p.Filename
if filename == "" {
return fmt.Sprintf("%d:%d", p.Line, p.Column)
}
return fmt.Sprintf("%s:%d:%d", filename, p.Line, p.Column)
}
// A Token returned by a Lexer.
type Token struct {
// Type of token. This is the value keyed by symbol as returned by Definition.Symbols().
Type rune
Value string
Pos Position
}
// RuneToken represents a rune as a Token.
func RuneToken(r rune) Token {
return Token{Type: r, Value: string(r)}
}
// EOF returns true if this Token is an EOF token.
func (t Token) EOF() bool {
return t.Type == EOF
}
func (t Token) String() string {
if t.EOF() {
return "<EOF>"
}
return t.Value
}
func (t Token) GoString() string {
if t.Pos == (Position{}) {
return fmt.Sprintf("Token{%d, %q}", t.Type, t.Value)
}
return fmt.Sprintf("Token@%s{%d, %q}", t.Pos.String(), t.Type, t.Value)
}
// MakeSymbolTable builds a lookup table for checking token ID existence.
//
// For each symbolic name in "types", the returned map will contain the corresponding token ID as a key.
func MakeSymbolTable(def Definition, types ...string) (map[rune]bool, error) {
symbols := def.Symbols()
table := map[rune]bool{}
for _, symbol := range types {
rn, ok := symbols[symbol]
if !ok {
return nil, fmt.Errorf("lexer does not support symbol %q", symbol)
}
table[rn] = true
}
return table, nil
}
|
