;'< Tests for functionality "Evaluate Robin Expression (with literal)" `symbol?` evaluates its argument, then evaluates to `#t` if it is a symbol, `#f` otherwise. | (symbol? (literal this-symbol)) = #t Numbers are not symbols. | (symbol? 9) = #f Lists are not symbols. | (symbol? (prepend 1 ())) = #f The argument to `symbol?` may (naturally) be any type, but there must be exactly one argument. | (symbol? 77 88) ? abort (illegal-arguments (77 88)) | (symbol?) ? abort (illegal-arguments ()) '<