Make protocol assertions show nicer errors for selected expression types

[MichaelClerx]

E.g. "assert x == 2" could return "Assertion failed: 2000 != 2" instead of just "Assertain failed" with "x == 2" somewhere in the stacktrace

[MichaelClerx]

This works, but is probably not OK for some reason

class Assert(AbstractStatement):
    """
    Assertion used within a protocol.
    """
    def __init__(self, expr):
        super(Assert, self).__init__()
        self.expr = expr

    def evaluate(self, env):
        result = self.expr.evaluate(env)
        try:
            ok = result.value
        except AttributeError:
            raise ProtocolError("Assertion did not yield a Simple value or 0-d Array.")
        if not ok:
            if isinstance(self.expr, E.Eq):
                operands = self.expr.evaluate_children(env)
                lhs = operands[0].value
                rhs = operands[1].value
                raise ProtocolError(f'Assertion failed: {lhs} != {rhs}.')
            raise ProtocolError("Assertion failed.")
        return V.Null()

[jonc125]

That sounds reasonable to me!

[MichaelClerx]

It may be worth it to add a close() method to the protocol language, that shows both arguments (unless they're vectors) ?