PL0 编译程序Turbo Pascal代码

麻雀虽小，五脏具全，对编译原理的代码以TPASCAL格式重新整理和排版，还原最原版的代码

编译版和例子下载：

http://www.skywind.me/maker/pl0-pas.rar

(********************* PL0 编译程序Turbo Pascal代码 *********************)
program pl0(fa,fa1,fa2);
(* PL0 compile with code generation *)

label 99;
      (* Turbo Pascal do not support goto between different
         blocks so, the 'goto' command in getch are replaced
         by procedure exitp !! in another way, 'label 99' do
         not work !!                  Lin Wei       2001  *)

const norw=13;       (* of reserved words *)
      txmax=100;     (* length of identifier table *)
      nmax=14;       (* max number of digits in numbers *)
      al=10;         (* length of identifiers *)
      amax=2047;     (* maximum address *)
      levmax=3;      (* max depth of block nesting *)
      cxmax=200;     (* size of code array *)

type symbol=(nul,ident,number,plus,minus,times,slash,oddsym,
             eql,neq,lss,leq,gtr,geq,lparen,rparen,comma,
             semicolon,period,becomes,beginsym,endsym,ifsym,
             thensym,whilesym,writesym,readsym,dosym,callsym,
             constsym,varsym,procsym);
     alfa=packed array[1..al] of char;
     objects=(constant,variable,procedur);
     (* wirth used the word "procedure"and"object" there, which won't work! *)
     symset=set of symbol;
     fct=(lit,opr,lod,sto,cal,int,jmp,jpc);
     instruction=packed record
                    f:fct;        (* function code *)
                    l:0..levmax;  (* level *)
                    a:0..amax;    (* displacement addr *)
                 end;
              (* lit 0,a load constant a
                 opr 0,a execute opr a
                 lod 1,a load variable 1,a
                 sto 1,a store variable 1,a
                 cal 1,a call procedure at level 1
                 int 0,a increment t -register by a
                 jmp 0,a jump to a
                 jpc 0,a jump conditional to a *)

var fa:text;
    fa1,fa2:text;
    listswitch:boolean;    (* true set list object code *)
    ch:char;               (* last char read *)
    sym:symbol;            (* last symbol read *)
    id:alfa;               (* last identifier read *)
    num:integer;           (* last number read *)
    cc:integer;            (* character count *)
    ll:integer;            (* line length *)
    kk:integer;
    cx:integer;            (* code allocation index *)
    line:array[1..81] of char;
    a:alfa;
    code:array[0..cxmax] of instruction;
    word:array[1..norw] of alfa;
    wsym:array[1..norw] of symbol;
    ssym:array[' '..'^'] of symbol;
        (* wirth uses "array[char]" here *)
    mnemonic:array[fct] of packed array[1..5] of char;
    declbegsys, statbegsys, facbegsys:symset;
    table:array[0..txmax] of record
            name:alfa;
            case kind:objects of
              constant:(val:integer);
              variable,procedur:(level,adr,size:integer)
            (* "size" lacking in original. I think it belongs here *)
          end;
    fin,fout:text;
    fname:string;
    err:integer;
    endf:boolean;

procedure error(n:integer);
begin
  writeln('****','':cc-1,'!',n:2);
  writeln(fa1,'****','':cc-1,'!',n:2);
  err:=err+1;
end; (* error *)

procedure exitp;
begin
  endf:=true;
  close(fin);
  writeln;
  exit;
end;

procedure getsym;
var i,j,k:integer;

  procedure getch;
  begin
    if cc=ll then begin
      if eof(fin) then begin
         write('program incomplete');
         close(fin);
         writeln;
         exitp;
         (*goto 99;*)
      end;
      ll:=0;
      cc:=0;
      write(cx:4,' ');
      write(fa1,cx:4,' ');
      while not eoln(fin) do begin
        ll:=ll+1;
        read(fin,ch);
        write(ch);
        write(fa1,ch);
        line[ll]:=ch;
      end;
      writeln;
      ll:=ll+1;
      (* read(fin,line[ll]); repleaced by two lines below *)
      line[ll]:=' ';
      readln(fin);
      writeln(fa1);
    end;
    cc:=cc+1;
    ch:=line[cc];
  end; (* getch *)

begin (* getsym *)
  while ch=' ' do getch;
  if ch in ['a'..'z'] then begin
     k:=0;
     repeat
       if k<al then begin
          k:=k+1;
          a[k]:=ch;
       end;
       getch;
     until not(ch in ['a'..'z','0'..'9']);
     if k>=kk then kk:=k
     else repeat
            a[kk]:=' ';
            kk:=kk-1;
          until kk=k;
     id:=a;
     i:=1;
     j:=norw;
     repeat
       k:=(i+j) div 2;
       if id<=word[k] then j:=k-1;
       if id>=word[k] then i:=k+1;
     until i>j;
     if i-1>j then sym:=wsym[k] else sym:=ident;
  end else if ch in ['0'..'9'] then begin (* number *)
    k:=0;
    num:=0;
    sym:=number;
    repeat
      num:=10*num+(ord(ch)-ord('0'));
      k:=k+1;
      getch;
    until not(ch in['0'..'9']);
    if k>nmax then error(30);
  end else if ch=':' then begin
    getch;
    if ch='=' then begin
       sym:=becomes;
       getch;
    end else sym:=nul;
  end else if ch='<' then begin
    getch;
    if ch='=' then begin
       sym:=leq;
       getch;
    end else sym:=lss;
  end else if ch='>' then begin
    getch;
    if ch='=' then begin
       sym:=geq;
       getch;
    end else sym:=gtr;
  end else begin
    sym:=ssym[ch];
    getch;
  end;
end; (* getsym *)

procedure gen(x:fct;y,z:integer);
begin
  if cx>cxmax then begin
     write('program too long');
     (*goto 99;*)
  end;
  with code[cx] do begin
       f:=x;
       l:=y;
       a:=z;
  end;
  cx:=cx+1;
end; (* gen *)

procedure test(s1,s2:symset;n:integer);
begin
  if not(sym in s1) then begin
     error(n);
     s1:=s1+s2;
     while not(sym in s1) do getsym;
  end;
end; (* test *)

procedure block(lev,tx:integer;fsys:symset);
var dx:integer;   (* data allocation index *)
    tx0:integer;  (* inital table index *)
    cx0:integer;  (* inital code index *)
    procedure enter(k:objects);
    begin (* enter object into table *)
      tx:=tx+1;
      with table[tx] do begin
        name:=id;
        kind:=k;
        case k of
          constant: begin
                      if num>amax then begin error(31); num:=0; end;
                      val:=num;
                    end;
          variable: begin
                      level:=lev;
                      adr:=dx;
                      dx:=dx+1;
                    end;
          procedur: level:=lev;
        end;
      end;
    end; (* enter *)

    function position(id:alfa):integer;
    var i:integer;
    begin (* find identifier in table *)
      table[0].name:=id;
      i:=tx;
      while table[i].name<>id do i:=i-1;
      position:=i;
    end; (* position *)

    procedure constdeclaration;
    begin
      if sym=ident then begin
         getsym;
         if sym in [eql,becomes] then begin
            if sym=becomes then error(1);
            getsym;
            if sym=number then begin
               enter(constant);
               getsym;
            end else error(2);
         end else error(3);
      end else error(4);
    end; (* constdeclaration *)

    procedure vardeclaration;
    begin
      if sym=ident then begin
         enter(variable);
         getsym;
      end else error(4);
    end; (* vardeclaration *)

    procedure listcode;
    var i:integer;
    begin
      if listswitch then begin
         for i:=cx0 to cx-1 do
             with code[i] do begin
                  writeln(i,mnemonic[f]:5,l:3,a:5);
                  writeln(fa,i:4,mnemonic[f]:5,l:3,a:5);
             end;
      end;
    end; (* listcode *)

    procedure statement(fsys:symset);
    var i,cx1,cx2:integer;
        procedure expression(fsys:symset);
        var addop:symbol;
            procedure term(fsys:symset);
            var mulop:symbol;
                procedure factor(fsys:symset);
                var i:integer;
                begin
                  test(facbegsys,fsys,24);
                  while sym in facbegsys do begin
                    if sym=ident then begin
                       i:=position(id);
                       if i=0 then error(11)
                       else with table[i] do
                         case kind of
                           constant:gen(lit,0,val);
                           variable:gen(lod,lev-level,adr);
                           procedur:error(21);
                         end;
                       getsym;
                    end else if sym=number then begin
                        if num>amax then begin
                           error(31);
                           num:=0;
                        end;
                        gen(lit,0,num);
                        getsym;
                    end else if sym=lparen then begin
                        getsym;
                        expression([rparen]+fsys);
                        if sym=rparen then getsym
                        else error(22);
                    end;
                    test(fsys,facbegsys,23);
                  end;
                end; (* factor *)

            begin (* term *)
              factor([times,slash]+fsys);
              while sym in [times,slash] do begin
                mulop:=sym;
                getsym;
                factor(fsys+[times,slash]);
                if mulop=times then gen(opr,0,4) else gen(opr,0,5)
              end;
            end; (* term *)

        begin (* expression *)
          if sym in [plus,minus] then begin
             addop:=sym;
             getsym;
             term(fsys+[plus,minus]);
             if addop=minus then gen(opr,0,1);
          end else term(fsys+[plus,minus]);
          while sym in [plus,minus] do begin
            addop:=sym;
            getsym;
            term(fsys+[plus,minus]);
            if addop=plus then gen(opr,0,2) else gen(opr,0,3);
          end;
        end; (* expression *)

        procedure condition(fsys:symset);
        var relop:symbol;
        begin
          if sym=oddsym then begin
             getsym;
             expression(fsys);
             gen(opr,0,6);
          end else begin
             expression([eql,neq,lss,leq,gtr,geq]+fsys);
             if not(sym in [eql,neq,lss,leq,gtr,geq]) then error(20)
             else begin
               relop:=sym;
               getsym;
               expression(fsys);
               case relop of
                 eql:gen(opr,0,8);
                 neq:gen(opr,0,9);
                 lss:gen(opr,0,10);
                 geq:gen(opr,0,11);
                 gtr:gen(opr,0,12);
                 leq:gen(opr,0,13);
               end;
             end;
          end;
        end; (* condition *)

    begin (* statement *)
      if sym=ident then begin
         i:=position(id);
         if i=0 then error(11)
         else if table[i].kind<>variable then begin
           error(12);
           i:=0;
         end;
         getsym;
         if sym=becomes then getsym else error(13);
         expression(fsys);
         if i<>0 then with table[i] do gen(sto,lev-level,adr);
      end else if sym=readsym then begin
         getsym;
         if sym<>lparen then error(34)
         else repeat
                getsym;
                if sym=ident then i:=position(id)
                else i:=0;
                if i=0 then error(35)
                else with table[i] do begin
                  gen(opr,0,16);
                  gen(sto,lev-level,adr);
                end;
                getsym;
         until sym<>comma;
         if sym<>rparen then begin
            error(33);
            while not(sym in fsys) do getsym;
         end else getsym;
      end else if sym=writesym then begin
         getsym;
         if sym=lparen then begin
            repeat
              getsym;
              expression([rparen,comma]+fsys);
              gen(opr,0,14);
            until sym<>comma;
            if sym<>rparen then error(33) else getsym;
         end;
         gen(opr,0,15);
      end else if sym=callsym then begin
         getsym;
         if sym<>ident then error(14)
         else begin
           i:=position(id);
           if i=0 then error(11) else with table[i] do
              if kind=procedur then gen(cal,lev-level,adr)
              else error(15);
           getsym;
         end;
      end else if sym=ifsym then begin
         getsym;
         condition([thensym,dosym]+fsys);
         if sym=thensym then getsym
         else error(16);
         cx1:=cx;
         gen(jpc,0,0);
         statement(fsys);
         code[cx1].a:=cx;
      end else if sym=beginsym then begin
         getsym;
         statement([semicolon,endsym]+fsys);
         while sym in [semicolon]+statbegsys do begin
           if sym=semicolon then getsym
           else error(10);
           statement([semicolon,endsym]+fsys);
         end;
         if sym=endsym then getsym else error(17);
      end else if sym=whilesym then begin
         cx1:=cx;
         getsym;
         condition([dosym]+fsys);
         cx2:=cx;
         gen(jpc,0,0);
         if sym=dosym then getsym else error(18);
         statement(fsys);
         gen(jmp,0,cx1);
         code[cx2].a:=cx;
      end;
      test(fsys,[],19);
    end; (* statement *)

begin (* block *)
  dx:=3;
  tx0:=tx;
  table[tx].adr:=cx;
  gen(jmp,0,0);
  if lev>levmax then error(32);
  repeat
    if sym=constsym then begin
       getsym;
       repeat
         constdeclaration;
         while sym=comma do begin
           getsym;
           constdeclaration;
         end;
         if sym=semicolon then getsym else error(5);
       until sym<>ident;
    end;
    if sym=varsym then begin
       getsym;
       repeat;
         vardeclaration;
         while sym=comma do begin
           getsym;
           vardeclaration;
         end;
         if sym=semicolon then getsym else error(5);
       until sym<>ident;
    end;
    while sym=procsym do begin
      getsym;
      if sym=ident then begin
         enter(procedur);
         getsym;
      end else error(4);
      if sym=semicolon then getsym else error(5);
      block(lev+1,tx,[semicolon]+fsys);
      if sym=semicolon then begin
         getsym;
         test(statbegsys+[ident,procsym],fsys,6);
      end else error(5);
    end;
    test(statbegsys+[ident],declbegsys,7);
  until not(sym in declbegsys);
  code[table[tx0].adr].a:=cx;
  with table[tx0] do begin
       adr:=cx;
       size:=dx;
  end;
  cx0:=cx;
  gen(int,0,dx);
  statement([semicolon,endsym]+fsys);
  gen(opr,0,0);
  test(fsys,[],8);
  listcode;
end; (* block *)

procedure interpret;
const stacksize=500;
var p,b,t:integer; (* program base topstack registers *)
    i:instruction;
    s:array[1..stacksize] of integer; (* datastore *)

    function base(l:integer):integer;
    var bl:integer;
    begin
      bl:=b; (* find base 1 level down *)
      while l>0 do begin
        bl:=s[bl];
        l:=l-1;
      end;
      base:=bl;
    end; (* base *)

begin
  writeln('start pl0');
  t:=0; b:=1; p:=0;
  s[1]:=0; s[2]:=0; s[3]:=0;
  repeat
    i:=code[p];
    p:=p+1;
    with i do case f of
      lit: begin t:=t+1; s[t]:=a; end;
      opr: case a of (* operator *)
             0: begin (* return *)
                  t:=b-1;
                  p:=s[t+3];
                  b:=s[t+2];
                end;
             1: s[t]:=-s[t];
             2: begin t:=t-1; s[t]:=s[t]+s[t+1]; end;
             3: begin t:=t-1; s[t]:=s[t]-s[t+1]; end;
             4: begin t:=t-1; s[t]:=s[t]*s[t+1]; end;
             5: begin t:=t-1; s[t]:=s[t] div s[t+1]; end;
             6: s[t]:=ord(odd(s[t]));
             8: begin t:=t-1; s[t]:=ord(s[t]=s[t+1]); end;
             9: begin t:=t-1; s[t]:=ord(s[t]<>s[t+1]); end;
             10:begin t:=t-1; s[t]:=ord(s[t]<s[t+1]); end;
             11:begin t:=t-1; s[t]:=ord(s[t]>=s[t+1]); end;
             12:begin t:=t-1; s[t]:=ord(s[t]>s[t+1]); end;
             13:begin t:=t-1; s[t]:=ord(s[t]<=s[t+1]); end;
             14:begin write(s[t]); write(fa2,s[t]); t:=t-1; end;
             15:begin writeln; writeln(fa2); end;
             16:begin t:=t+1; write('?'); write(fa2,'?'); readln(s[t]);
                writeln(fa2,s[t]); end;
           end;
      lod: begin t:=t+1; s[t]:=s[base(l)+a]; end;
      sto: begin s[base(l)+a]:=s[t]; (* writeln(s[t]) *) t:=t-1; end;
      cal: begin (* generat new block mark *) s[t+1]:=base(l); s[t+2]:=b;
           s[t+3]:=p; b:=t+1; p:=a; end;
      int: t:=t+a;
      jmp: p:=a;
      jpc: begin if s[t]=0 then p:=a; t:=t-1; end;
    end; (* with, case *)
  until p=0;
  close(fa2);
end; (* interpret *)

begin (* main *)
  for ch:=' ' to '!' do ssym[ch]:=nul;
  (* changed bacause of different character set
     note the typos below in the original where
     the alfas were not given the correct space *)
  word[1]:='begin     ';  word[2]:='call      ';
  word[3]:='const     ';  word[4]:='do        ';
  word[5]:='end       ';  word[6]:='if        ';
  word[7]:='odd       ';  word[8]:='procedure ';
  word[9]:='read      ';  word[10]:='then      ';
  word[11]:='var       '; word[12]:='while     ';
  word[13]:='write     ';

  wsym[1]:=beginsym;   wsym[2]:=callsym;
  wsym[3]:=constsym;   wsym[4]:=dosym;
  wsym[5]:=endsym;     wsym[6]:=ifsym;
  wsym[7]:=oddsym;     wsym[8]:=procsym;
  wsym[9]:=readsym;    wsym[10]:=thensym;
  wsym[11]:=varsym;    wsym[12]:=whilesym;
  wsym[13]:=writesym;

  ssym['+']:=plus;     ssym['-']:=minus;
  ssym['*']:=times;    ssym['/']:=slash;
  ssym['(']:=lparen;   ssym[')']:=rparen;
  ssym['=']:=eql;      ssym[',']:=comma;
  ssym['.']:=period;   ssym['#']:=neq;
  ssym[';']:=semicolon;

  mnemonic[lit]:='lit  ';  mnemonic[opr]:='opr  ';
  mnemonic[lod]:='lod  ';  mnemonic[sto]:='sto  ';
  mnemonic[cal]:='cal  ';  mnemonic[int]:='int  ';
  mnemonic[jmp]:='jmp  ';  mnemonic[jpc]:='jpc  ';

  declbegsys:=[constsym,varsym,procsym];
  statbegsys:=[beginsym,callsym,ifsym,whilesym];
  facbegsys:=[ident,number,lparen];

  (* page(output) *)
  endf:=false;
  assign(fa1,'PL0.txt');
  rewrite(fa1);
  write('input file? ');
  write(fa1,'input file?');
  readln(fname);
  writeln(fa1,fname);
  (* openf(fin,fname,'r'); ==> *)
  assign(fin,fname); reset(fin);
  write('list object code ?');
  readln(fname);
  write(fa1,'list object code ?');
  listswitch:=(fname[1]='y');
  err:=0;
  cc:=0; cx:=0; ll:=0;
  ch:=' '; kk:=al;
  getsym;
  assign(fa,'PL0-1.txt');
  assign(fa2,'PL0-2.txt');
  rewrite(fa);
  rewrite(fa2);
  block(0,0,[period]+declbegsys+statbegsys);
  close(fa);
  close(fa1);
  if sym<>period then error(9);
  if err=0 then interpret else write('error in pl/0 program');
99: (* this line is not work in turbo pascal so replace by
       procedure exitp: see the memo at the top *)
  close(fin);
  writeln;
end.