* module/language/cps/intmap.scm: Intmaps can now contain any value;
#f does not indicate the absence of a value. Instead we use a unique
private sentinel to mark absent values or branches.
(*absent*, absent?, present?): New helpers.
(new-branch): Initialize empty elements to *absent*.
(clone-branch-with-edit): New helper.
(clone-branch-and-set): Use clone-branch-with-edit.
(writable-branch): Use clone-branch-with-edit
(empty-intmap): Initialize value to *absent*.
(add-level): clone-branch-and-set doesn't take #f as a branch any
more; use new-branch.
(branch-empty?, make-intmap/prune, intmap-add!):
(intmap-add, intmap-remove, intmap-next, intmap-prev):
(intmap-fold, intmap-union, intmap-intersect): Use absent? to detect
absent branches / values.
(intmap-ref): Likewise. Instead of returning #f if the value is not
found, call the optional not-found procedure. By default this will
signal an error.
* module/language/cps/types.scm:
* module/language/cps2/renumber.scm:
* module/language/cps2/simplify.scm: Adapt to intmap-ref signalling an
error by default if the value is not found.
* module/language/tree-il/compile-cps2.scm: Adapt to intmap-add
signalling an error if #f was in the intmap as a value.
* module/language/tree-il/compile-cps2.scm (convert): Fix bug
in (apply - ...), because the instruction for "-" is "sub", and
"sub" lookup was failing. Caught by numbers.test. Really I would
like to get rid of $prim, somehow.
* module/language/tree-il/compile-cps2.scm (adapt-arity): New
procedure. This is equivalent to (language cps arities), but as it
is a necessary pass and not an optimization it's more proper to put
it in the converter itself. Unlike with the nested CPS
representation, it's possible to look up continuations without
making a DFG.
(convert): Adapt arities as necessary.
