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package lexer
// PeekingLexer supports arbitrary lookahead as well as cloning.
type PeekingLexer struct {
cursor int
eof Token
tokens []Token
}
// Upgrade a Lexer to a PeekingLexer with arbitrary lookahead.
func Upgrade(lex Lexer) (*PeekingLexer, error) {
r := &PeekingLexer{}
for {
t, err := lex.Next()
if err != nil {
return r, err
}
if t.EOF() {
r.eof = t
break
}
r.tokens = append(r.tokens, t)
}
return r, nil
}
// Cursor position in tokens.
func (p *PeekingLexer) Cursor() int {
return p.cursor
}
// Length returns the number of tokens consumed by the lexer.
func (p *PeekingLexer) Length() int {
return len(p.tokens)
}
// Next consumes and returns the next token.
func (p *PeekingLexer) Next() (Token, error) {
if p.cursor >= len(p.tokens) {
return p.eof, nil
}
p.cursor++
return p.tokens[p.cursor-1], nil
}
// Peek ahead at the n+1 token. ie. Peek(0) will peek at the next token.
func (p *PeekingLexer) Peek(n int) (Token, error) {
i := p.cursor + n
if i >= len(p.tokens) {
return p.eof, nil
}
return p.tokens[i], nil
}
// Clone creates a clone of this PeekingLexer at its current token.
//
// The parent and clone are completely independent.
func (p *PeekingLexer) Clone() *PeekingLexer {
clone := *p
return &clone
}
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