Return type inference and return value bound handling

[jitsedesmet]

Currently, the expression evaluator does not always return the type expected by the specs. For example right now the addition of two shorts will return an integer, it should however be a short to be compliant with the sparql spec, pointing to xpath spec.

If the two operands of an arithmetic expression are not of the same type, subtype substitution and numeric type promotion are used to obtain two operands of the same type.

While implementing this, we should also consider what should happen when the return value is out of bounds for the type. For example, what is the return value when a short is returned, but the value is too large to fit in a shot? Overflow? Cap? Widen the return type?

This is originally mentioned in an issue of the sparqlee repo: comunica/sparqlee#45.