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Declaration Blocks

• Hide details about implementation of a structure.
  • module GLOBAL-STACK =
    begin
       var CTR: newint,
       var STACK: array [1...100] of newint
    in
       proc PUSH(X: intexp) = ...
       proc POP = ...
       fun TOP = ...
       proc INIT = CTR:=0
    end
• Stack allocated on module definition.
• Body of declaration block made visible:
  • import GLOBAL-STACK
    in call INIT; call PUSH(0); ...
• Stack variable alive but not in scope!