bool contains(cstring_span<> word) const { return symbols_.find(word) != kNullIndex; }
bool contains(std::string const& word) const { return symbols_.find(word) != kNullIndex; }
Sym sym(std::string const& word) const { SymInt const i = symbols_.find(word); return i == kNullIndex ? NoSymbol : symForIndex(i); }
Sym sym(cstring_span<> word) const { SymInt const i = symbols_.find(word); return i == kNullIndex ? NoSymbol : symForIndex(i); }
SymInt index(std::string const& word) const { return symbols_.find(word); }