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;'<<SPEC'

### `list?` ###

    -> Tests for functionality "Interpret core Robin Program"

`list?` evaluates its argument, then evaluates to `#t` if it is a list,
`#f` otherwise.

    | (define literal (macro (s a e) (head a)))
    | (display
    |   (list? (literal (a b))))
    = #t

    | (define literal (macro (s a e) (head a)))
    | (display
    |   (list? (literal (a b c d e f))))
    = #t

    | (display
    |   (list? (prepend 4 (prepend 5 ()))))
    = #t

The empty list is a list.

    | (display
    |   (list? ()))
    = #t

Symbols are not lists.

    | (define literal (macro (s a e) (head a)))
    | (display
    |   (list? (literal a)))
    = #f

The argument to `list?` may (naturally) be any type, but there must be
exactly one argument.

    | (display
    |   (list? (prepend 4 ()) (prepend 6 ())))
    ? uncaught exception: (illegal-arguments ((prepend 4 ()) (prepend 6 ())))

    | (display
    |   (list?))
    ? uncaught exception: (illegal-arguments ())

'<<SPEC'