[ Course Documents ] : [ Implementing Subprograms ]

Previous Contents Next Keyword Index

Mechanics of Display References

• Use the display_offset to get the pointer into the display to the ARI with the variable

• Use the local_offset to get to the variable within the ARI

• Display maintenance (assuming no parameters that are subprograms and no pass-by-name parameters):
  • Display_offset depends only on the static_depth of the procedure whose ARI is being built: It is exactly the static_depth of the procedure
  • There are k+1 entries in the display, where k is the static depth of the currently executing unit (k=0 is for the main program)
  • For a call to procedure P with a static_depth of k:
    • Save a copy of the display pointer at position k in new ARI
    • Put the link to the new ARI for P at position k in the display
    • On return, move the saved display pointer from the ARI back into the display at position k