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On 29/02/12 13:28, Richard Hipp wrote:
>> We *could* keep track of each separate CHECK expression and remember
>> the constraint name and evaluate each expression separately and
>> output a customized error message for each failure. But that would
>> require a lot of extra code space, which is not "lite".
This is just bytecode. It requires one extra instruction per CHECK.
Currently the code for something like A AND B AND C should look something
like the following since you can abort the processing of an AND the moment
an arm is false.
1. Evaluate A
2. If not true, goto error
3. Evaluate B
4. If not true, goto error
5. Evaluate C
6. If not true, goto error
Inserting an extra opcode to set the error message isn't a huge overhead,
and is required once per arm. Or whatever is done for 'goto error' could
have a parameter pointing to the string name of the constraint.
A higher level approach depends on a 'raise' function, so A AND B AND C
can be rewritten to (A OR raise('A')) AND (B OR raise('B')) AND (C OR
raise('C'))
There is a reason developers have gone to the trouble of naming their
constraints!
Roger
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