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37 lines
695 B
37 lines
695 B
package lexer
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// Upgrade a Lexer to a PeekingLexer with arbitrary lookahead.
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func Upgrade(lexer Lexer) PeekingLexer {
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if peeking, ok := lexer.(PeekingLexer); ok {
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return peeking
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}
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return &lookaheadLexer{Lexer: lexer}
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}
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type lookaheadLexer struct {
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Lexer
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peeked []Token
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}
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func (l *lookaheadLexer) Peek(n int) (Token, error) {
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for len(l.peeked) <= n {
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t, err := l.Lexer.Next()
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if err != nil {
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return Token{}, err
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}
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if t.EOF() {
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return t, nil
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}
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l.peeked = append(l.peeked, t)
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}
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return l.peeked[n], nil
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}
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func (l *lookaheadLexer) Next() (Token, error) {
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if len(l.peeked) > 0 {
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t := l.peeked[0]
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l.peeked = l.peeked[1:]
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return t, nil
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}
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return l.Lexer.Next()
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}
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