;'<<SPEC'
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### `head` ###
-> Tests for functionality "Evaluate core Robin Expression"
`head` evaluates its argument to a list, and evaluates to the first element
of that list.
| (head (prepend #t ()))
= #t
`head` expects its argument to be a list.
| (head #f)
? abort (expected-list #f)
`head` expects exactly one argument.
| (head (prepend #t ()) (prepend #f ()))
? abort (illegal-arguments ((prepend #t ()) (prepend #f ())))
| (head)
? abort (illegal-arguments ())
`head` is basically equivalent to Scheme's `car`.
'<<SPEC'
(require head)