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Symbol Parsing Procedures in System Software: COP 3402 Code Generation Overview

This document outlines the symbol parsing procedures and declaration mechanisms used in the context of system software, specifically for COP 3402 in Summer 2013. It covers the structured handling of constant and variable declarations, procedural definitions, and various control statements, including conditions and loops. Key functions like `getsym()`, `constdeclaration()`, and `vardeclaration()` are explained alongside error checking algorithms. The code snippets detail the parsing logic, helping programmers understand the intricacies of symbol management in compiler design.

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Symbol Parsing Procedures in System Software: COP 3402 Code Generation Overview

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  1. Parser & Code Generation II COP 3402 System Software Summer 2013

  2. Enter Symbol

  3. Parsing Procedures

  4. Block declaration do { if (sym==constsym) { getsym(); do { constdeclaration(lev,&tx,&dx); while(sym==comma) { getsym(); constdeclaration(lev,&tx,&dx); } if(sym==semicolon)getsym(); else error(5); } while (sym==ident); } if (sym==varsym) { getsym(); do { vardeclaration(lev,&tx,&dx); while (sym==comma) { getsym(); vardeclaration(lev,&tx,&dx); } if(sym==semicolon) getsym(); else error(5); } while(sym==ident); } proc-declaration::= {"procedure" ident "; "block ";" } statement .

  5. else if TOKEN = "ifsym" then begin • GET(TOKEN); • CONDITION; • if TOKEN != "thensym" then ERROR; • GET(TOKEN); • STATEMENT • end • else if TOKEN = "whilesym" then begin • GET(TOKEN); • CONDITION; • if TOKEN != "dosym" then ERROR; • GET(TOKEN); • STATEMENT • end • end; procedure STATEMENT; begin if TOKEN = "identsym" then begin GET(TOKEN); if TOKEN != "becomessym" then ERROR; GET(TOKEN); EXPRESSION end else if TOKEN = "callsym" then begin GET(TOKEN); if TOKEN != "identsym" then ERROR; GET(TOKEN) end else if TOKEN = "beginsym" then begin GET TOKEN; STATEMENT; while TOKEN = "semicolomsym" do begin GET(TOKEN); STATEMENT end; if TOKEN != "endsym" then ERROR; GET(TOKEN) end

  6. Statement if (sym==callsym) { getsym(); if (sym!=ident) error(14); else { i=position(id, ptx); if(i==0) error(11); else if (table[i].kind==procedure) gen(cal,lev-table[i].level, table[i].adr); else error(15); getsym(); } } //statement ::= [ "call" ident | … ]

  7. Generating Code for lod and sto

  8. Statement if (sym==ident){ i=position(id,ptx); if(i==0) error(11); else if (table[i].kind!=variable) { error(12); i=0; }; getsym(); if (sym==becomes) getsym(); else error(13); expression(lev,ptx); if (i!=0) gen(sto, lev-table[i].level, table[i].adr); }

  9. Factor(lev, ptx) intlev, *ptx; { inti, level, adr, val; while ((sym==ident)||(sym==number)||(sym==lparen)){ if (sym==ident){ i=position(id,ptx); if (i==0) error(11); // undeclared identifier else{ kind=table[i].kind; level=table[i].level; adr=table[i].adr; val=table[i].val; if (kind==constant) gen(lit,0,val); else if (kind==variable) gen(lod,lev-level,adr); else error(21); // Expression must not contain a procedure identifier } getsym(); } else if(sym==number) { if (num>amax) {error(31); num=0;} gen(lit,0,num); getsym(); } else if(sym==lparen) { getsym(); expression(lev,ptx); if (sym==rparen)getsym(); else error(22); // Right parenthesis missing. } } } Factor Emit example

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