HELP with Wirth's Pascal0 Compiler

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Join Date: Nov 2007

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HELP with Wirth's Pascal0 Compiler

Nov 26th, 2007

Hey all, I have been stuck on this problem for weeks now. Basically I took a variation on Wirth's compiler and adding some more functionality to it. I needed to add FOR loop and CASE statement functionality to it.
I have the bulk of both of them done but when I input a test input file (labeled as 'valid.pas' in the code) it either hangs up when I run it or doesn't output anything.

here is the code for both statements. I have also attached the full compiler which can be compiled using any free pascal compiler. (**Just change from .txt to .pas**)

CASE Statement

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 casesym:begin
                { Code for CASE }
             {counter declared as a global}
             counter:=0;
             getsym;
             expression;
             if sym <> ofsym then error(27);
              getsym;
              while sym <> cendsym do;
              begin
               getsym;
               if sym <> constsym then error(29);
               getsym;
               counter := counter + 1; {count # of cases}

               gen(CTS,0,0); {copy to top of stack}
               gen(LIT,0,table[i].adr); {get value of const}
               gen(OPR,0,8); {=}
               cx1:=codeinx; {save codeinx}
               gen(JPC,0,0);

               if sym <> colon then error(39);
               getsym;
               statement;
               if sym <> semicolon then error(17);
               getsym;
               if counter = 1 then
                 begin
                   cx2:=codeinx;
                   gen(JMP,0,0);
                 end
               else
                 gen(JMP,0,cx2);

              end;
              {cend has been found}
              code[cx2].ad:=codeinx;
              gen(INT,0,-1); {get rid of copied value on stk }
         end;

FOR Loop

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forsym:begin
                { Code for FOR }
             getsym;
             if sym <> ident then error(11);
             i:=position(id);
             if i=0 then error(11);
              if table[i].kind <> variable then error(37);
              getsym;
             if sym <> becomes then error(38);
              getsym;
              expression;
              gen(STO,lev-table[i].level,table[i].adr);
             if not (sym in [tosym, downtosym]) then error(11);
              sym2:=sym; {store TO/DOWNTO}
              getsym;
              expression;
              cx1:=codeinx;
              {}
               gen(STO,0,0);
               gen(LOD,lev,table[i].adr);
               if sym2=tosym then gen(OPR,0,12){to}
               else
               gen(OPR,0,13); {downto}
               cx2:=codeinx;
               gen(JPC,0,0);
              {}
             if sym <> dosym then error(18);
              getsym;
              statement;
              gen(LOD,lev,table[i].adr);
              gen(LIT,0,1);

              if sym2=tosym then gen(OPR,0,2) {add}
              else
               gen(OPR,0,1);{subtract}

              gen(STO,0,0);
              gen(JMP,0,cx1); {jump back}
              code[cx2].ad:=codeinx;

        end;

Thanks for your help

Attached Files