I am experimenting with registering my own compiler for the "regex"
language, but the usage is confusing. It seems that the intention is
that compilers will return a code object that gets invoked, at which
time it runs until it hits an C<end> opcode. But what if I want to
return some values from the compiled code? I see the following
options:
1) Manually set up the return values in the appropriate registers.
2) Use .pcc_begin_return/.pcc_end_return to set up the return values,
but override the P1 return continuation to go to some subroutine
that immediately calls C<end>.
3) Use .pcc_begin_return/.pcc_end_return to set up the return values,
and have the user of the compiler grab out some magic-named
subroutine using C<find_global> and invoke it rather than directly
invoking the return value of the C<compile> op.
4) Make my compiler behave differently from the built-in compilers,
by arranging for it to return a Sub object from the C<compile> op
rather than an Eval object. Then the caller can directly invoke
the return value of C<compile> and get back return values as if
it were calling a normal subroutine, because it is.
#1 is painful and extremely error-prone.
#2 is a total hack.
#3 forces the user of the compiler to not only call things differently
depending on which language it's using, but also it has to know the
magic subroutine name
#4 seems to make compilers inconsistent with each other, and I worry that
the Eval PMC does more than just running code until it hits an C<end> op.
If my explanation was confusing, then here are some examples. I expect
the user of the compiler to look like this:
$P0 = compreg "pig-latin"
$P1 = compile $P0, "eturnray oneay oremay anthay asway assedpay inay"
$I0 = $P1(41)
print $I0 # Should print out 42
Option #3 would change this to
$P0 = compreg "pig-latin"
compile $P0, "eturnray oneay oremay anthay asway assedpay inay"
$P1 = find_global "_pig_latin_eval_block"
$I0 = $P1(41)
print $I0 # Should print out 42
Rather than writing out example code for the compiler and generated
code to illustrate each of the cases, I think I'll wait to see if this
needs clarification first. :-)
