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Show It s^aumtAo», th« ptttpos« ®t a &mi%mfctim i» t» er^iiii «tad dfttaxnln« tht'soop« of « nrnti väildk Mil @«rv« «i a Idkoli or r«pr«a«nt«tlv« of some Iast$tta$@ eleraent«. A HMM hat M It« Mopa tho <lM»dy> in which it %mm 4ool«ro«. Sinoo both tyf ani top01O9y may he as@ifned ä^naatcallf aotliiatff aoro nood be dono than to list the new nstnoo for oaoh <body>. Itaw doclaratiens may be considered to be exeeiitod-in the eenee that a vector consisting of undefined ▼aluea (Q) it created in the runtime stack for th® duration of the block. Fositiona in the vector correspond to each identifier declared. Jttetifioation« Block structure has proved to be an estremelv useful aM important concept in ALGOLic langixafos. Besides aidinf the proframmer freatly in his own debugginf# block structure is also the ideal way t® delimit the scope of users in a nultiprogramming and/©r time-sharing environment. Examplesi Aibegin '''«fbjC are local to block A.'•' new a.,h,c. a"«-a+(b+c-2) ; B:begin new a. ••'this a*is local to' block B and supersedes''• •*b+c+2; '''the previous declaration, b,c are''' end •«»from block A.•'' •♦■•+2l '''thiB a is the one declared in Block A''' end |
