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package lexer
// FlaggableLexer wraps a lexer, automatically translating tokens based on flags, if any.
type FlaggableLexer struct {
lex *Lexer // a reference to the lexer used for tokenization
enabledFlags map[string]transformer // flags that are enabled
seenDefinition bool
afterUseIdentifier bool
}
// NewFlaggableLexer returns a new FlaggableLexer for the given lexer.
func NewFlaggableLexer(lex *Lexer) *FlaggableLexer {
return &FlaggableLexer{
lex: lex,
enabledFlags: map[string]transformer{},
}
}
// Close stops the lexer from running.
func (l *FlaggableLexer) Close() {
l.lex.Close()
}
// NextToken returns the next token found in the lexer.
func (l *FlaggableLexer) NextToken() Lexeme {
nextToken := l.lex.nextToken()
// Look for `use somefeature`
if nextToken.Kind == TokenTypeIdentifier {
// Only allowed until we've seen a definition of some kind.
if !l.seenDefinition {
if l.afterUseIdentifier {
if transformer, ok := Flags[nextToken.Value]; ok {
l.enabledFlags[nextToken.Value] = transformer
}
l.afterUseIdentifier = false
} else {
l.afterUseIdentifier = nextToken.Value == "use"
}
}
}
if nextToken.Kind == TokenTypeKeyword && nextToken.Value == "definition" {
l.seenDefinition = true
}
if nextToken.Kind == TokenTypeKeyword && nextToken.Value == "caveat" {
l.seenDefinition = true
}
for _, handler := range l.enabledFlags {
updated, ok := handler(nextToken)
if ok {
return updated
}
}
return nextToken
}
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