add multiple values support to the vm
* libguile/vm-engine.c (vm_run): The bootstrap program now uses mv_call,
so as to allow multiple values out of the VM. (It did before, because
multiple values were represented internally as single scm_values
objects, but now that values go on the stack, we need to note the boot
frame as accepting multiple values.)
(vm_error_no_values): New error, happens if you pass no values into a
single-value continuation. Passing more than one is OK though, it just
takes the first one.
* libguile/vm-i-system.c (halt): Assume that someone has pushed the
number of values onto the stack, and package up that number of values
as a scm_values() object, for communication with the interpreter.
(mv-call): New instruction, calls a procedure with a multiple-value
continuation, even handling calls out to the interpreter.
(return/values): New instruction, returns multiple values to the
continuation. If the continuation is single-valued, takes the first
value or errors if there are no values. Otherwise it returns to the
multiple-value return address, pushing the number of values on top of
the values.
* module/system/il/compile.scm (codegen): Compile <ghil-values> forms.
* module/system/il/ghil.scm (<ghil-values>) Add new GHIL data structure
and associated procedures.
* module/language/scheme/translate.scm (custom-transformer-table):
Compile (values .. ) forms into <ghil-values>.