;'<<SPEC'
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### `symbol?` ###
-> 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 ())
'<<SPEC'
(require symbol?)