I have looked at parser transformations of logical operators
and they are needed to provide short circuit evaluation.
I see the following solutions:
1) declare that 'and' and 'or' are reserved only for Boolean
arguments, that they have short circuit semantics and
leave transformations in place
2) make sure that 'and' and 'or' when applied to Boolean
use short circuit semantics
3) declare that 'and' and 'or' evaluate arguments and
change algebra to no longer depend on short circuit
evaluation
4) declare that 'and' and 'or' evaluate arguments but
introduce new operators with short circuit semantics
and use them instead of 'and' and 'or'
I admit that 1) looks most attractive for me.
AFAICS 2) can not work really well: if in generic code 'and'
and 'or' would evaluate arguments even if the actual
type is Boolean -- this means change of semantics
between generic case and case of concrete type.
Also, making such distinction just on type basis
introduces ugly irregularity to the language definition.
I consider 3) as inpractical. Namely, my experience
with Standard Pascal (which specifies full evaluation
of arguments to 'and' and 'or') is that this complicates
programming as one must introduce extra conditionals
to avoid errors in subexpressions that otherwise would
be guarded by circuit evaluation.
Concerning 4), it could work, but I am not sure if
non-Boolean use of 'and' and 'or' is important enough
to take traditional names -- ATM I feel that use
as programming construct is more important.
--
Waldek Hebisch
[email protected]
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