     [ defs-vregs ] [ temp-vregs ] [ uses-vregs ] tri 3append ;
 
 M: vreg-insn assign-registers-in-insn
-    active-intervals get over all-vregs '[ vreg>> _ member? ] filter
+    active-intervals get seq>> over all-vregs '[ vreg>> _ member? ] filter
     [ [ vreg>> ] [ reg>> ] bi ] { } map>assoc
     >>regs drop ;
 
 M: insn assign-registers-in-insn drop ;
 
+: <active-intervals> ( -- obj )
+    V{ } clone active-intervals boa ;
+
 : init-assignment ( live-intervals -- )
-    V{ } clone active-intervals set
+    <active-intervals> active-intervals set
     <min-heap> unhandled-intervals set
     init-unhandled ;
 


: expire-old-intervals ( n -- )
    active-intervals get
    swap '[ end>> _ = ] partition
    active-intervals set
    [ insert-spill ] each ;

: insert-reload ( live-interval -- )

! but since we never have too many machine registers (around 30
! at most) and we probably won't have that many live at any one
! time anyway, it is not a problem to check each element.
TUPLE: active-intervals seq ;

: add-active ( live-interval -- )
    active-intervals get seq>> push ;

: lookup-register ( vreg -- reg )
    active-intervals get seq>> [ vreg>> = ] with find nip reg>> ;

! Minheap of live intervals which still need a register allocation
SYMBOL: unhandled-intervals
