[syntax] check expr (=> equal) expected)

[syntax] check expr => expected)

SRFI-78: evaluates expr and compares the value to the value of expected using the predicate equal, which is equal? when omitted. Then a report is printed according to the current mode setting (see check-set-mode!) and the outcome is recorded in a global state to be used in check-report. The precise order of evaluation is that first equal and expected are evaluated (in unspecified order) and then expr is evaluated.