On 4/3/24 18:41, Waldek Hebisch wrote:
Well, AFAICS this is one of limitations of current compiler: 'error'
gets special treatment, but only when it is translated to Boot
function called 'error'. If you rename 'error3' to 'error', then
the file will compile. But I expect that such rename will cause
trouble, so I do not think it is a practical solution.
That actually brings me to the question whether overloading in BOOT is
also supposed to work, i.e., whether I can have
error(x) == errorSupervisor($AlgebraError,x)
error(con, fun, mess) ==
errorSupervisor($AlgebraError, [STRCONC(fun, '" $ ", con, '": "),
mess])
at the same time. I guess no.
BTW: my guess is that trouble is due to following pattern:
piv2 = 0 => error "impossible 3"
...
lf1 := rquo(rp, rw)
lf1 := lf1 + nc2*lop
Thanks to special treatment of 'error' compiler knows that
lf1 is well defined at the end of this sequence. But
without special treatment compiler thinks that 'lf1' may
be undefined when the sequence is finished.
One could work around this by giving lf1 and rf1 explicit
type declarations at start of 'lift1', like:
lf1 : YDP
rf1 : YDP
but this is somewhat suboptimal, as it needs more code and
weakens compiler checking.
OK, that would have been something that I would have tried to do, but I
could not see how this would be related to the error3 function.
Even now I do not quite see it. Looks like type checking is done after
compForm1 was executed so that the typechecker sees error3 and does not
know that this, in fact, includes a RETURN-FROM-FUNCTION.
OK, that are compiler internals that I am not so much interested in.
However, your statement about the declarations bothered me a bit.
First of all, I do not think that declaring the types of variables is a
bad idea, since it is an easy hint for the programmer to understand the
code. So that point of your "suboptimal" does not count for me.
However, you say something about "weakens compiler checking", and that I
don't understand at all. Up to know I would have guessed that when I
declare the type of a variable, the compiler also checks that in places
where this variable is used (or assigned), the actual types match with
what I have declared. Is this not the case?
Ralf
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