Incorrect terminology in error message for invalid fail statement

[pubudu91]

Consider the snippet below:

public function foo(json|error data) returns json {
    if (data is error) {
        fail data;
    } else {
        return data;
    }
}

The error given to the above is:

invalid usage of the 'fail' expression operator: no matching error return type(s) in the enclosing invokable

I don't think it's correct to call it the "fail expression operator" seeing at it's a statement. Need to reword this error message to,

1. Correct the terminology
2. Convey what went wrong in a better way

[MaryamZi]

Issue in terminology applies to check/checkpanic errors too.

invalid usage of the 'check' expression operator: all expression types are equivalent to error type
invalid usage of the 'check' expression operator: no expression type is equivalent to error type
invalid usage of the 'checkpanic' expression operator: no expression type is equivalent to error type