pascals.txt

program Pascals(input+,output);     (*1.6.75*)
(*        N. Wirth,  E.T.H.
          Clausiusstr.55   CH-8006 Zurich    *)
label 99;
const nkw = 27;     (*no. of key words*)
    alng =  10;     (*no. of significant chars in identifiers*)
    llng = 120;     (*input line length*)
    emax = 322;     (*max exponent of real numbers*)
    emin =-292;     (*min exponent*)
    kmax =  15;     (*max no. of significant digits*)
    tmax = 100;     (*size of table*)
    bmax =  20;     (*size of block-table*)
    amax =  38;     (*size of array-table*)
    c2max = 20;     (*size of real constant table*)
    csmax = 30;     (*max no. of cases*)
    cmax = 850;     (*size of code*)
    lmax =   7;     (*maximum level*)
    smax = 600;     (*size of string-table*)
    ermax = 58;     (*max error no.*)
    omax =  63;     (*highest order code*)
    xmax = 131071;  (*2**17 - 1*)
    nmax = 281474976710655;   (*2**48-1*)
    lineleng = 136; (*output line length*)
    linelimit = 200;
    stacksize = 1500;

type symbol = (intcon,realcon,charcon,string,
               notsy,plus,minus,times,idiv,rdiv,imod,andsy,orsy,
               eql,neq,gtr,geq,lss,leq,
               lparent,rparent,lbrack,rbrack,comma,semicolon,period,
               colon,becomes,constsy,typesy,varsy,functionsy,
               proceduresy,arraysy,recordsy,programsy,ident,
               beginsy,ifsy,casesy,repeatsy,whilesy,forsy,
               endsy,elsesy,untilsy,ofsy,dosy,tosy,downtosy,thensy);

    index  = -xmax .. +xmax;
    alfa = packed array [1..alng] of char;
    object = (konstant,variable,type1,prozedure,funktion);
    types  = (notyp,ints,reals,bools,chars,arrays,records);
    symset = set of symbol;
    typset = set of types;
    item   = record
               typ: types; ref: index;
             end ;
    order  = packed record
               f: -omax..+omax;
               x: -lmax..+lmax;
               y: -nmax..+nmax;
             end ;

var sy: symbol;          (*last symbol read by insymbol*)
    id: alfa;            (*identifier from insymbol*)
    inum: integer;       (*integer from insymbol*)
    rnum: real;          (*real number from insymbol*)
    sleng: integer;      (*string length*)
    ch: char;            (*last character read from source program*)
    line: array [1..llng] of char;
    cc: integer;         (*character counter*)
    lc: integer;         (*program location counter*)
    ll: integer;         (*length of current line*)
    errs: set of 0..ermax;
    errpos: integer;
    progname: alfa;
    iflag, oflag: boolean;
    constbegsys,typebegsys,blockbegsys,facbegsys,statbegsys: symset;
    key: array [1..nkw] of alfa;
    ksy: array [1..nkw] of symbol;
    spa: array [char] of symbol;  (*special symbols*)

    t,a,b,sx,c1,c2: integer;  (*indices b tables*)
    stantyps: typset;
    display: array [0 .. lmax] of integer;

    tab:     array [0 .. tmax] of     (*identifier table*)
               packed record
                 name: alfa;  link: index;
                 obj: object; typ: types;
                 ref: index;  normal: boolean;
                 lev: 0 .. lmax; adr: integer;
               end ;
    atab:    array [0 .. amax] of     (*array-table*)
               packed record
                 indtyp, eltyp: types;
                 elref, low, high, elsize, size: index;
               end ;
    btab:    array [0 .. bmax] of    (*block-table*)
               packed record
                  last, lastpar, psize, vsize: index
               end ;
    stab:    packed array [0..smax] of char;  (*string table*)
    rconst:  array [1 .. c2max] of real;
    code:    array [0 .. cmax] of order;

procedure errormsg;
   var k: integer;
       msg: array [0..ermax] of alfa;
begin
  msg[ 0] := 'undef id  '; msg[ 1] := 'multi def ';
  msg[ 2] := 'identifier'; msg[ 3] := 'program   ';
  msg[ 4] := ')         '; msg[ 5] := ':         ';
  msg[ 6] := 'syntax    '; msg[ 7] := 'ident, var';
  msg[ 8] := 'of        '; msg[ 9] := '(         ';
  msg[10] := 'id, array '; msg[11] := '[         ';
  msg[12] := ']         '; msg[13] := '..        ';
  msg[14] := ';         '; msg[15] := 'func. type';
  msg[16] := '=         '; msg[17] := 'boolean   ';
  msg[18] := "convar typ'; msg[19] := 'type      ';
  msg[20] := "prog.param'; msg[21] := 'too big   ';
  msg[22] := '.         '; msg[23] := 'typ (case)';
  msg[24] := 'character '; msg[25] := 'const id  ';
  msg[26] := 'index type'; msg[27] := 'indexbound';
  msg[28] := 'no array  '; msg[29] := 'type id   ';
  msg[30] := 'undef type'; msg[31] := 'no record ';
  msg[32] := 'boole type'; msg[33] := 'arith type';
  msg[34] := 'integer   '; msg[35] := 'types     ';
  msg[36] := 'param type'; msg[37] := 'variab id ';
  msg[38] := 'string    '; msg[39] := 'no.of pars';
  msg[40] := 'type      '; msg[41] := 'type      ';
  msg[42] := 'real type '; msg[43] := 'integer   ';
  msg[44] := 'var, const'; msg[45] := 'var, proc ';
  msg[46] := 'types (:=)'; msg[47] := 'typ (case)';
  msg[48] := 'type      '; msg[49] := 'store ovf1';
  msg[50] := 'constant  '; msg[51] := ':=        ';
  msg[52] := 'then      '; msg[53] := 'until     ';
  msg[54] := 'do        '; msg[55] := 'to downto ';
  msg[56] := 'begin     '; msg[57] := 'end       ';
  k := 0; writeln; writeln(' key words');
  while errs <> [] do
  begin while not (k in errs) do k := k+1;
        writeln(k,'  ',msg[k]); errs := errs - [k]
  end
end (*errormsg*) ;

procedure nextch;   (*read next character; process line end*)
begin if cc = ll then
      begin if eos(input) then
            begin writeln;
               writeln(' program incomplete');
               errormsg; goto 99
            end ;
         if errpos <> 0 then
            begin writeln; errpos := 0
            end ;
         write(lc:5, '  ');
         ll := 0; cc := 0;
         while not eo1n(input) do
            begin ll := ll+1; read(ch); write(ch); line[ll] := ch
            end ;
         writeln; ll := ll+1: read(1ine[ll])
      end ;
   cc := cc+1; ch := 1ine[cc];
end (*nextch*) ;

procedure error(n: integer);
begin if errpos = 0 then write(' ****');
   if cc > errpos then
      begin write(' ': cc-errpos, '^', n:2);
         errpos := cc+3; errs := errs + [n]
      end
end (*error*) ;

procedure fatal(n: integer);
   var msg: array [1..7] of a1fa;
begin writeln; errormsg;
   msg[ 1] := 'identifier'; msg[ 2] := 'procedures';
   msg[ 3] := 'reals     '; msg[ 4] := 'arrays    ';
   msg[ 5] := 'levels    '; msg[ 6] := 'code      ';
   msg[ 7] := 'strings   ';
   write1n(' compiler table for ', msg[n], ' is too small');
   goto 99    (* terminate compilation*)
end (*fatal*) ;

procedure insymbol;           (*reads next symbol*)
   label 1,2,3;
   var i,j,k,e: integer;

   procedure readscale;
      var s, sign: integer;
   begin nextch; sign := 1; s := 0;
      if ch = '+' then nextch else
      if ch = '-' then begin nextch; siqn := -1 end ;
      while ch in ['0'..'9'] do
         begin s := 10*s + ord(ch) - ord('0'); nextch
         end ;
      e := s*sign + e
   end (*readscale*) ;

   procedure adjustscale;
      var s: integer; d,t: real;
   begin if k+e > emax then error(21) else
         if k+e < emin then rnum := 0 else
     begin s := abs(e); t := 1.0; d := 10.0;
       repeat
         while not odd(s) do
            begin s := s div 2; d := sqr(d)
            end ;
         s := s-1; t := d*t
       until s = 0;
       if e >= 0 then rnum := rnum*t else rnum := rnum/t
     end
   end (*adjustscale*) ;

begin (*insymbol*)
1: while ch = ' ' do nextch;
   if ch in ['a'..'z'] then
   begin (*word*)  k := 0; id := '          ';
      repeat if k < alng then
             begin k := k+1; id[k] := ch
             end ;
         nextch
      until not (ch in ['a'..'z','0'..'9']);
      i := 1; j := nkw;   (*binary search*)
      repeat k := (i+j) div 2;
         if id <= key[k] then j := k-1;
         if id >= key[k] then i := k+1
      until i > j;
      if i-1 > j then sy := ksy[k] else sy := ident
   end else
   if ch in ['0'..'9'] then
   begin (*number*) k := 0; inum := 0; sy := intcon;
      repeat inum := inum*10 + ord(ch) - ord('0');
         k := k+1; nextch
      until not (ch in ['0'..'9']);
      if (k > kmax) or (inum > nmax) then
        begin error(21); inum := 0; k := 0
        end ;
      if ch = '.' then
      begin nextch;
         if ch '.' then ch := ':' else
            begin sy := realcon; rnum := inum; e := 0;
               while ch in ['0'..'9'] do
               begin e := e-1;
                  rnum := 10.0*rnum + (ord(ch)-ord('0')); nextch
               end ;
               if ch = 'e' then readscale;
               if e <> 0 then adjustscale
            end
      end else
      if ch = 'e' then
      begin sy := realcon; rnum := inum; e := 0;
         readscale; if e <> 0 then adjustscale
      end ;
   end else
   case ch of
':' : begin nextch;
          if ch = '=' then
            begin sy :=  becomes; nextch
            end  else sy := colon
      end ;
'<' : begin nextch;
         if ch = '=' then begin sy := leq; nextch end else
         if ch = '>' then begin sy := neq; nextch end else sy := lss
      end ;
'>' : begin nextch;
         if ch = '=' then begin sy := geq; nextch end else sy := gtr
      end ;
'.' : begin nextch;
         if ch = '.' then
            begin sy := colon; nextch
            end  else sy := period
'''': begin k := 0;
    2:  nextch;
        if ch = '''' then
          begin nextch; if ch <> '''' then goto 3
          end ;
        if sx+k = smax then fatal(7);
        stab[sx+k] := ch; k := k+1;
        if cc = 1 then
          begin (*end of line*) k := 0;
          end
        else goto 2;
    3:  if k = 1 then
           begin sy := charcon; inum := ord(stab[sx])
           end else
        if k = 0 then
           begin error(38); sy := charcon; inum := 0
           end else
           begin sy := string; inum := sx; sleng := k; sx := sx+k
           end
      end ;
'(' : begin nextch;
         if ch <> '*' then sy := lparent else
         begin (*comment*) nextch;
            repeat
               while ch <> '*' do nextch;
               nextch
            until ch = ')';
            nextch; goto 1
         end
      end ;
'+', '-', '*', '/', ')', '=', ',', '[', ']', '#', '&', ':' :
      begin sy := sps[ch]; nextch
'$', '%', '@', '\', '~', '{', '}', '^' :
      begin error(24); nextch; goto 1
      end
   end
end (*insymbol*) ;

procedure enter(x0: alfa; x1: object;
                x2: types; x3: integer);
begin t := t+1;   (*enter standard identifier*)
   with tab[t] do
   begin name := x0; link := t-1; obj := x1;
      typ := x2; ref := 0; normal := true;
      lev := 0: adr := x3
   end
end (*enter*) ;

procedure enterarray(tp: types; l,h: integer);
begin if l > h then error(27);
   if (abs(l)>xmax) or (abs(h)>xmax) then
      begin error(27); l := 0; h := 0;
      end ;
   if a = amax then fata1(4) else
      begin a := a+1;
         with atab[a] do
             begin inxtyp := tp; low := 1; high := h
             end
      end
end (*enterarray*) ;

procedure enterblock;
begin if b = bmax then fatal(2) else
      begin b := b+1; btab[b].last := 0; btab[b].lastpar := 0
      end
end (*enterblock*) ;

procedure enterreal(x: real);
begin if c2 = c2max-1 then fatal(3) else
      begin rconst[c2+1] := x; c1 := 1;
         while rconst[c1] <> x do  c1 := c1+1;
         if c1 > c2 then c2 := c1
      end
end (*enterreal*) ;

procedure emit(fct: integer);
begin if lc = cmax then fatal(6);
   code[lc].f := fct; lc := lc+1
end (*emit*) ;

procedure emit1(fct,b: integer);
begin if lc = cmax then fatal(6);
   with code[lc] do
      begin f := fct; y := b end ;
   lc := lc+1
end (*emit1*) ;

procedure emit2(fct,a,b: integer);
begin if lc = cmax then fatal(6);
   with code[lc] do
     begin f := fct; x := a; y := b end ;
   lc := lc+1
end (*emit2*) ;

procedure printtables;
   var i: integer; o: order;
begin
   writeln('0identifiers     link  obj  typ  ref  nrm  lev  adr');
   for i := btab[1].last +1 to t do
      with tab[i] do
      writeln(i,' ',name,link:5, ord(obj):5, ord(typ):5, ref:5,
            ord(normal):5, lev:5, adr:5);
   writeln('0blocks    last lpar psze vsze');
   for i := 1 to b do
      with btab[i] do
      writeln(i, last:5, lastpar:5, psize:5, vsize:5);
   writeln('0arrays    xtyp etyp eref  low high elsz size');
   for i := 1 to a do
      with atab[i] do
      writeln(i, ord(inxtyp):5, ord(eltyp):5,
              elref:5, low:5, high:5, elsize:5, size:5);
   writeln('0code:');
   for i := 0 to lc-1 do
   begin if i mod 5 = 0 then
         begin writeln; write(i:5)
         end ;
      o := code[i]; write(o.f:5);
      if o.f < 31 then
        if o.f < 4 then write(o.x:2, o.y:5)
                    else write(o.y:7)
      else write('       ');
      write(',')
   end ;
   writeln
end (*printtables*) ;

procedure block(fsys: symset; isfun: boolean; level: integer);
   type conrec =
      record case tp: types of
         ints,chars,bools: (i: integer);
         reals: (r: real)
      end ;

   var dx: integer;    (*data allocation index*)
       prt: integer;   (*t-index of this procedure*)
       prb: integer;   (*b-index of this procedure*)
       x: integer;

   procedure skip(fsys: symset; n: integer);
   begin error(n);
      while not (sy in fsys) do insymbol
   end (*skip*) ;

   procedure test(s1,s2: symset; n: integer);
   begin if not (sy in s1) then
      skip(s1+s2,n)
   end (*test*) ;

   procedure testsemicolon;
   begin
      if sy = semicolon then insymbol else
      begin error(14);
        if sy in [comma,colon] then insymbol
      end ;
      test([ident]+blockbegsys, fsys, 6)
   end (*testsemicolon*) ;

   procedure enter(id: alfa; k: object);
      var j,l: integer;
   begin if t = tmax then fatal(1) else
         begin tab[0].name := id;
            j := btab[display[level]].last;  1 := j;
            while tab[j].name <> id do  j := tab[j].link;
            if j <> 0 then error(1) else
            begin t := t+1;
              with tab[t] do
              begin name := id; link := l;
               obj := k; typ := notyp; ref := 0; lev := level;
               adr := 0
              end ;
              btab[display[level]].last := t
            end
         end
   end (*enter*) ;

   function loc(id: alfa): integer;
      var i,j: integer;     (*locate id in table*)
   begin i := level; tab[0].name := id;   (*sentinel*)
      repeat j := btab[display[i]].last;
         while tab[j].name <> id do  j := tab[j].link;
         i := i-1;
      until (i<0) or (j<>0);
      if j = 0 then error(0);  loc := j
   end (*loc*) ;

  procedure entervariable;
  begin if sy = ident then
          begin enter(id,variable); insymbol
          end
        else error(2)
  end (*entervariable*) ;

   procedure constant(fsys: symset; var c: conrec);
     var x, sign: integer;
   begin c.tp := notyp; c.i := 0;
     test(constbegsys, fsys, 50);
     if sy in constbegsys then
     begin
         if sy = charcon then
           begin c.tp := chars; c.i := inum; insymbol
           end
         else
           begin sign := 1;
             if sy in [plus,minus] then
               begin if sy = minus then sign := -1;
                 insymbol
               end ;
             if sy = ident then
               begin x := loc(id);
                 if x <> 0 then
                   if tab[x].obj <> konstant then error(25) else
                   begin c.tp := tab[x].typ;
                     if c.tp = reals
                          then c.r := sign*rconst[tab[x].adr]
                          else c.i := sign*tab[x].adr
                   end ;
                 insymbol
               end
             else
             if sy = intcon then
               begin c.tp := ints; c.i := sign*inum; insymbol
               end else
             if sy = realcon then
               begin c.tp := reals; c.r := sign*rnum; insymbol
               end else skip(fsys,50)
           end;
         test(fsys, [], 6)
       end
   end (*constant*) ;

   procedure typ(fsys: symset; var tp: types; var rf, sz: integer);
     var x: integer;
         eltp: types; elrf: intager;
         elsz, offset, t0,t1:  integer;

     procedure arraytyp(var aref,arsz: integer);
        var eltp: types;
            low, high: conrec;
            elrf, elsz: integer;
     begin constant([colon,rbrack,rparent,ofsy]+fsys, low);
        if low.tp = reals then
           begin error(27); low.tp := ints; low.i := 0
           end ;
        if sy = colon then insymbol else error(13);
        constant([rbrack,comma,rparent,ofsy)+fsys, high);
        if high.tp <> low.tp then
           begin error(27); high.i := low.i
           end ;
        enterarray(low.tp, low.i, high.i); aref := a;
        if sy = comma then
           begin insymbol; eltp := arrays; arraytyp(elrf,elsz)
           end else
        begin
           if sy = rbrack then insymbol else
              begin error(12);
                 if sy = rparent then insymbol
              end ;
           if sy = ofsy then insymbol else error(8);
           typ(fsys,eltp,elrf,elsz)
        end ;
        with atab[aref] do
        begin arsz := (high-low+1)*elsz; size := arsz;
           eltyp := eltp; elref := elrf; elsize := elsz
        end ;
     end (*arraytyp*) ;

   begin (*typ*) tp := notyp; rf := 0; sz := 0;
     test(typebegsys, fsys, 10);
     if sy in typebegsys then
       begin
         if sy = ident then
         begin x := loc(id);
           if x <> 0 then
           with tab[x] do
             if obj <> type1 then error(29) else
             begin tp := typ; rf := ref; sz := adr;
               if tp = notyp then error(30)
             end ;
           insymbol
         end else
         if sy = arraysy then
         begin insymbol;
             if sy = lbrack then insymbol else
                begin error(11);
                   if sy = lparent then insymbol
                end ;
             tp := arrays; arraytyp(rf,sz)
         end else
         begin (*records*) insymbol;
           enterblock; tp := records; rf := b;
           if level = lmax then fatal(5);
           level := level+1; display[level] := b; offset := 0;
           while sy <> endsy do
           begin (*field section*)
             if sy = ident then
             begin t0 := t; entervariable;
               while sy = comma do
                 begin insymbol; entervariable
                 end ;
               if sy = colon then insymbol else error(5);
               t1 := t;
               typ(fsys+[semicolon,endsy,comma,ident],
                   eltp,elrf,elsz);
               while t0 < t1 do
               begin t0 := t0+1;
                 with tab[t0] do
                 begin typ := eltp; ref := elrf; normal := true;
                   adr := offset; offset := offset + elsz
                 end
               end
             end ;
             if sy <> endsy then
             begin if sy = semicolon then insymbol else
                   begin error(14);
                     if sy = comma then insymbol
                   end ;
                test([ident,endsy,semicolon], fsys, 6)
             end
           end ;
           btab[rf].vsize := offset; sz := offset;
           btab[rf].psize := 0; insymbol; level := level-1
         end ;
         test(fsys, [], 6)
       end
   end (*typ*) ;

   procedure parameterlist;     (*formal parameter list*)
      var tp: types;
          rf, sz, x, t0: integer;
          valpar: boolean;
   begin insymbol; tp := notyp; rf := 0; sz := 0;
     test([ident, varsy], fsys+[rparent], 7);
     while sy in [ident,varsy] do
       begin if sy <> varsy then valpar := true else
               begin insymbol; valpar := false
               end ;
         t0 := t; entervariable;
         while sy = comma do
            begin insymbol; entervariable;
            end ;
         if sy = colon then
           begin insymbol;
             if sy <> ident then error(2) else
             begin x := loc(id); insymbol;
               if x <> 0 then
               with tab[x] do
                 if obj <> type1 then error(29) else
                   begin tp := typ; rf := ref;
                     if valpar then sz := adr else sz := 1
                   end ;
             end ;
             test([semicolon,rparent], [comma,ident]+fsys, 14)
           end
         else error(5);
         while t0 < t do
         begin t0 := t0+1;
           with tab[t0] do
           begin typ := tp; ref := rf;
               normal := valpar; adr := dx; lev := level;
               dx := dx + sz
           end
         end ;
         if sy <> rparent then
         begin if sy = semicolon then insymbol else
               begin error(14);
                 if sy = comma then insymbol
               end ;
            test([ident,varsy], [rparent]+fsys, 6)
         end
       end (*while*) ;
     if sy = rparent then
       begin insymbol;
         test([semicolon,colon], fsys, 6)
       end
     else error(4)
   end (*parameterlist*) ;

   procedure constantdeclaration;
     var c: conrec;
   begin insymbol;
     test([ident], blockbegsys, 2);
     while sy = ident do
       begin enter(id,konstant); insymbol;
         if sy = eql then insymbol else
            begin error(16);
               if sy = becomes then insymbol
            end ;
         constant([semicolon,comma,ident]+fsys,c);
         tab[t].typ := c.tp; tab[t].ref := 0;
         if c.tp = reals then
           begin enterreal(c.r); tab[t].adr := c1 end
         else tab[t].adr := c.i;
         testsemicolon
       end
   end (*constantdeclaration*) ;

   procedure typedeclaration;
     var tp: types; rf, sz, t1: integer;
   begin insymbol;
     test([ident], blockbegsys, 2);
     while sy = ident do
       begin enter(id,type1); t1 := t; insymbol;
         if sy = eql then insymbol else
            begin error(16);
               if sy = becomes then insymbol
            end ;
         typ([semicolon,comma,ident]+fsys, tp, rf, sz);
         with tab[t1] do
           begin typ := tp; ref := rf; adr := sz
           end ;
         testsemicolon
       end
   end (*typedeclaration*) ;

   procedure variabledeclaration;
     var t0, t1, rf, sz: integer;
         tp: types;
   begin insymbol;
     while sy = ident do
     begin t0 := t; entervariable;
       while sy = comma do
         begin insymbol; entervariable;
         end ;
       if sy = colon then insymbol else error(5);
       t1 := t;
       typ([semicolon, comma, ident]+fsys, tp,  rf,  sz);
       while t0 < t1 do
       begin t0 := t0+1;
         with tab[t0] do
         begin typ := tp; ref := rf;
           lev := level; adr := dx; normal := true;
           dx := dx + sz
         end
       end ;
       testsemicolon
     end
   end (*variabledeclaration*) ;

   procedure procdeclaration;
      var isfun: boolean;
   begin isfun := sy = functionsy; insymbol;
     if sy <> ident then
        begin  error(2); id := '          '
        end ;
     if isfun then enter(id,funktion) else enter(id,prozedure);
     tab[t].normal := true;
     insymbol; block([semicolon]+fsys, isfun, level+1);
     if sy = semicolon then insymbol else error(14);
     emit(32+ord(isfun))    (*exit*)
   end (*proceduredeclaration*) ;



   procedure statement(fsys: symset);
      var i: integer; x: item;
      procedure expression(fsys: symset; var x: item); forward;

      procedure selector(fsys: symset; var v:item);
         var x: item; a,j: integer;
      begin (*sy in [lparent, lbrack, period]*)
        repeat
          if sy = period then
          begin insymbol;  (*field selector*)
            if sy <> ident then error(2) else
            begin
              if v.typ <> records then error(31) else
              begin (*search field identifier*)
                j := btab[v.ref] .last; tab[0].name := id;
                while tab[j].name <> id do j := tab[j].link;
                if j = 0 then error(0);
                v.typ := tab[j].typ; v.ref := tab[j].ref;
                a := tab[j].adr; if a <> 0 then emit1(9,a)
              end ;
              insymbol
            end
          end else
          begin (*array selector*)
            if sy <> lbrack then error(11);
            repeat insymbol;
              expression(sys+[comma,rbrack], x);
              if v.typ <> arrays then error(28) else
                begin a := v.ref;
                  if atab[a].inxtyp <> x.typ then error(26) else
                if atab[a].elsize = 1 then emit1(20,a)
                                      else emit1(21,a);
                  v.typ := atab[a].eltyp: v.ref := atab[a].elref
                end
            until sy <> comma;
            if sy = rbrack then insymbol else
              begin error(12); if sy = rparent then insymbol
              end
          end
        until not (sy in [lbrack,lparent,period]);
        test(fsys, [], 6)
      end (*selector*) ;

      procedure call(fsys: symset; i: integer);
         var x: item;
             lastp, cp, k: integer;
      begin emit1(18,i);  (*mark stack*)
        lastp := btab[tab[i].ref].lastpar; cp := i;
        if sy = lparent then
        begin (*actual parameter list*)
          repeat insymbol;
            if cp >= lastp then error(39) else
            begin cp := cp+1;
              if tab[cp].normal then
              begin (*value parameter*)
                expression(fsys+[comma,colon,rparent], x);
                if x.typ=tab[cp].typ then
                  begin
                    if x.ref <> tab[cp].ref then error(36) else
              if x.typ = arrays then emit1(22,atab[x.ref].size) else
                 if x.typ = records then emit1(22,btab[x.ref].vsize)
                  end else
                if (x.typ=ints) and (tab[cp].typ=reals) then
                   emit1(26,0) else
                   if x.typ<>notyp then error(36);
              end else
              begin (*variable parameter*)
                if sy <> ident then error(2) else
                begin k := loc(id); insymbol;
                  if k <> 0 then
                  begin if tab[k].obj <> variable then error(37);
                    x.typ := tab[k].typ; x.ref := tab[k].ref;
                    if tab[k].normal
                       then emit2(0,tab[k].lev,tab[k].adr)
                       else emit2(1,tab[k].lev,tab[k].adr);
                    if sy in [lbrack,lparent,period] then
                       selector(fsys+[comma,colon,rparent], x);
                    if (x.typ<>tab[cp].typ) or (x.ref<>tab[cp].ref)
                    then error(36)
                  end
                end
              end
            end ;
            test([comma,rparent], fsys, 6)
          until sy <> comma;
          if sy = rparent then insymbol else error(4)
        end ;
        if cp < lastp then error(39); (*too few actual parameters*)
        emit1(19, btab[tab[i].ref].psize-1);
        if tab[i].lev < level then emit2(3, tab[i].lev, level)
      end (*call*) ;

      function resulttype(a,b: types): types;
      begin
        if (a>reals) or (b>reals) then
          begin error(33); resulttype := notyp
          end else
        if (a=notyp) or (b=notyp) then resulttype := notyp else
        if a=ints then
          if b=ints then resulttype := ints else
            begin resulttype := reals; emit1(26,1)
            end
        else
          begin resulttype := reals;
            if b=ints then emit1(26,0)
          end
      end (*resulttype*) ;

      procedure expression;
        var y:item; op:symbol;

        procedure simpleexpression(fsys:symset; var x:item);
          var y:item; op:symbol;

          procedure term(fsys:symset; var x:item);
            var y:item; op:symbol; ts:typset;

            procedure factor(fsys:symset; var x:item);
              var i,f: integer;

              procedure standfct(n: integer);
                 var ts: typset;
              begin (*standard function no. n*)
                if sy = lparent then insymbol else error(9);
                if n < 17 then
                  begin expression(fsys+[rparent],x);
                    case n of
(*abs,sqr*)      0,2:  begin ts := [ints,reals];
                         tab[i].typ := x.typ;
                         if x.typ = reals then n := n+1
                       end ;
(*odd,chr*)      4,5:  ts := [ints];
(*ord*)            6:  ts := [ints,bools,chars];
(*succ,pred*)    7,8:  ts := [chars];
(*round,trunc*)  9,10,11,12,13,14,15,16:
(*sin,cos,...*)        begin ts := [ints,reals];
                         if x.typ = ints then emit1(26,0)
                       end ;
                    end ;
                    if x.typ in ts then emit1(8,n) else
                    if x.typ <> notyp then error(48);
                  end else
(*eof,eoln*)      begin (*n in [17,18]*)
                    if sy <> ident then error(2) else
                  if id <> 'input     ' then error(0) else insymbol;

                    emit1(8,n);
                  end ;
                x.typ := tab[i].typ;
                if sy = rparent then insymbol else error(4)
              end (*standfct*) ;

            begin (*factor*) x.typ := notyp; x.ref := 0;
              test(facbegsys, fsys, 58);
              while sy in facbegsys do
                begin
                  if sy = ident then
                  begin i := loc(id); insymbol;
                    with tab[i] do
                    case obj of
              konstant: begin x.typ := typ; x.ref := 0;
                          if x.typ = reals then
                            emit1(25,adr) else
                            emit1(24,adr)
                        end ;
              variable: begin x.typ := typ; x.ref := ref;
                          if sy [lbrack,lparent,period] then
                            begin if normal then f := 0 else f := 1;
                              emit2(f, lev, adr);
                              selector(fsys,x);
                              if x.typ in stantyps then emit(34)
                            end else
                            begin
                              if x.typ in stantyps then
                                if normal then f := 1 else f := 2
                              else
                                if normal then f := 0 else f := 1;
                              emit2(f, lev, adr)
                            end
                        end ;
              type1, prozedure:    error(44);
              funktion :begin x.typ := typ;
                          if lev <> 0 then call(fsys, i)
                                else standfct(adr)
                        end
                    end (*case,with*)
                  end else
                  if sy in [charcon,intcon,realcon] then
                   begin
                     if sy = realcon then
                     begin x.typ := reals; enterreal(rnum);
                       emit1(25, c1)
                     end else
                     begin if sy = charcon then x.typ := chars
                                           else x.typ := ints;
                       emit1(24, inum)
                     end ;
                     x.ref := 0; insymbol
                   end else
                  if sy = lparent then
                   begin insymbol; expression(fsys+[rparent], x);
                     if sy = rparent then insymbol else error(4)
                   end else
                  if sy = notsy then
                   begin insymbol; factor(fsys,x);
                     if x.typ=bools then emit(35) else
                       if x.typ<>notyp then error(32)
                   end ;
                  test(fsys, facbegsys, 6)
                end (*while*)
            end (*factor*) ;
          begin (*term*)
            factor(fsys+[times,rdiv,idiv,imod,andsy], x);
            while sy in [times,rdiv,idiv.imod,andsy] do
              begin op := sy; insymbol;
                factor(fsys+[times,rdiv,idiv,imod,andsy), y);
                if op = times then
                begin x.typ := resulttype(x.typ, y.typ);
                  case x.typ of
                    notyp: ;
                    ints : emit(57);
                    reals: emit(60);
                  end
                end else
                if op = rdiv then
                begin
                  if x.typ = ints then
                    begin emit1(26,1); x.typ := reals
                    end ;
                  if y.typ = ints then
                    begin emit1(26,0); y.typ := reals
                    end ;
                  if (x.typ=reals) and (y.typ=reals) then
                    emit(61) else
                    begin if (x.typ<>notyp) and (y.typ<>notyp) then
                            error(33);
                          x.typ := notyp
                    end
                end else
                if op = andsy then
                begin if (x.typ=bools) and (y.typ=bools) then
                         emit(56) else
                      begin if (x.typ<>notyp) and (y.typ<>notyp)
                          then error(32);
                         x.typ := notyp
                      end
                end else
                begin (*op in [idiv, imod]*)
                  if (x.typ=ints) and (y.typ=ints) then
                    if op=idiv then emit(58)
                               else emit(59) else
                    begin if (x.typ<>notyp) and (y.typ<>notyp) then
                             error(34);
                          x.typ := notyp
                    end
                end
              end
          end (*term*) ;
        begin (*simpleexpression*)
          if sy in [plus,minus] then
            begin op := sy; insymbol;
              term(fsys+[plus,minus], x);
              if x.typ > reals then error(33) else
                if op = minus then emit(36)
            end else
          term(fsys+[plus,minus,orsy], x);
          while sy in [plus,minus,orsy] do
            begin op := sy; insymbol;
               term(fsys+[plus,minus,orsy], y);
               if op = orsy then
               begin
                 if (x.typ=bools) and (y.typ=bools) then emit(51) else
                     begin if (x.typ<>notyp) and (y.typ<>notyp) then
                              error(32);
                           x.typ := notyp
                     end
               end else
               begin typ := resulttype(x.typ, y.typ);
                 case x.typ of
                   notyp: ;
                   ints : if op = plus then emit(52)
                                   else emit(53);
                   reals: if op = plus then emit(54)
                                   else emit(55)
                 end
               end
            end
        end (*simpleexpression*) ;
      begin (*expression*)
        simpleexpression(fsys+[eql,neq,lss,leq,gtr,geq], x);
        if sy in [eql,neq,lss,leq,gtr,geq] then
          begin op := sy; insymbol;
            simpleexpression(fsys, y);
            if (x.typ in [ notyp,ints,bools,chars]) and
               (x.typ = y.typ) then
              case op of
                eql: emit(45);
                neq: emit(46);
                lss: emit(47);
                leq: emit(48);
                gtr: emit(49);
                geq: emit(50);
              end else
            begin if x.typ = ints then
                    begin x.typ := reals; emit1(26,1)
                    end else
                  if y.typ = ints then
                    begin y.typ := reals; emit1(26,0)
                    end ;
              if (x.typ=reals) and (y.typ=reals) then
                case op of
                  eql: emit(39);
                  neq: emit(40);
                  lss: emit(41);
                  leq: emit(42);
                  gtr: emit(43);
                  geq: emit(44);
                end
              else error(35)
            end ;
            x.typ := bools
         end
     end (*expression*) ;

    procedure assignment(lv,ad: integer);
       var x,y: item; f: integer;
       (*tab[i].obj in [variable,prozedure]*)
    begin x.typ := tab[i].typ; x.ref := tab[i].ref;
      if tab[i].normal then f := 0 else f := 1;
      emit2(f, lv, ad);
      if sy in [lbrack,lparent,period] then
         selector([becomes,eql]+fsys, x);
      if sy = becomes then insymbol else
        begin error(51); if sy = eql then insymbol
        end ;
      expression(fsys, y);
      if x.typ = y.typ then
        if x.typ in stantyps then emit(38) else
        if x.ref <> y.ref then error(46) else
        if x.typ = arrays then emit1(23, atab[x.ref].size)
                          else emit1(23, btab[x.ref].vsize)
      else
      if (x.typ=reals) and (y.type=ints) then
        begin emit1(26,0); emit(38)
        end else
        if (x.typ<>notyp) and (y.typ<>notyp) then error(46)
    end (*assignment*) ;

    procedure compoundstatement;
    begin insymbol;
      statement([semicolon,endsy]+fsys);
      while sy in [semicolon]+statbegsys do
      begin if sy = semicolon then insymbol else error(14);
        statement([semicolon,endsy]+fsys)
      end ;
      if sy = endsy then insymbol else error(57)
    end (*compoundstatement*) ;

    procedure ifstatement;
       var x: item; lc1,lc2: integer;
    begin insymbol;
      expression(fsys+[thensy,dosy], x);
      if not (x.typ in [bools,notyp]) then error(17);
      lc1 := lc; emit(11);  (*jmpc*)
      if sy = thensy then insymbol else
        begin error(52); if sy = dosy then insymbol
        end ;
      statement(fsys+{elsesy]);
      if sy = elsesy then
        begin insymbol; lc2 := lc; emit(10);
          code[lc1].y := lc: statement(fsys); code[lc2].y := lc
        end
      else code[lc1].y := lc
    end (*ifstatement*) ;

    procedure casestatement;
      var x: item;
          i,j,k,lc1: integer;
          casetab: array [1..csmax] of
                     packed record val, lc: index end
          exittab: array [1..csmax] of integer;

      procedure caselabel;
        var lab: conrec; k: integer;
      begin constant(fsys+[comma,colon], lab);
        if lab.tp <> x.typ then error(47) else
        if i = csmax then fatal(6) else
          begin i := i+1; k := 0;
            casetab[i].val := lab.i; casetab[i].lc := lc;
            repeat k := k+1 until casetab[k].val = lab.i;
            if k < i then error(1);   (*multiple definition*)
          end
      end (*caselabel*) ;

      procedure onecase;
      begin if sy in constbegsys then
        begin caselabel;
          while sy = comma do
            begin insymbol; caselabel
            end ;
          if sy = colon then insymbol else error(5);
          statement([semicolon,endsy]+fsys);
          j := j+1; exittab[j] := lc; emit(10)
        end
      end (*onecase*) ;

    begin insymbol; i := 0; j := 0;
      expression(fsys+[ofsy,comma,colon], x);
      if not (x.typ in [ints,bools,chars,notyp]) then error(23);
      lc1 := lc; emit(12);  (*jmpx*)
      if sy = ofsy then insymbol else error(8);
      onecase;
      while sy = semicolon do
        begin insymbol; onecase
        end ;
      code[lc1].y := lc;
      for k := 1 to i do
        begin emit1(13,casetab[k].val); emit1(13,casetab[k].lc)
        end ;
      emit1(10,0);
      for k := 1 to j do code[exittab[k]].y := lc;
      if sy = endsy then insymbol else error(57)
    end (*casestatement*) ;

    procedure repeatstatement;
       var x: item; lc1: integer;
    begin lc1 := lc;
      insymbol; statement([semicolon,untilsy]+fsys);
      while sy in [semicolon]+statbegsys do
      begin if sy = semicolon then insymbol else error(14);
        statement([semicolon,untilsy]+fsys)
      end ;
      if sy = untilsy then
        begin insymbol; expression(fsys, x);
          if not (x.typ in [bools,notyp]) then error(17);
          emit1(11,lc1)
        end
      else error(53)
    end (*repeatstatement*) ;

    procedure whilestatement;
       var x: item; lc1,lc2: integer;
    begin insymbol; lc1 := lc;
      expression(fsys+[dosy], x);
      if not (x.typ in [bools,notyp]) then error(17);
      lc2 := lc; emit(11);
      if sy = dosy then insymbol else error(54);
      statement(fsys); emit1(10,lc1); code[lc2].y := lc
    end (*whilestatement*) ;

    procedure forstatement;
       var cvt: types; x: item;
           i,f,lc1,lc2: integer;
    begin insymbol;
      if sy = ident then
        begin i := loc(id); insymbol;
          if i = 0 then cvt := ints else
          if tab[i].obj = variable then
            begin cvt := tab[i].typ;
              emit2(0, tab[i].lev, tab[i].adr);
              if not (cvt in [notyp,ints,bools,chars])
                 then error(18)
            end else
            begin error(37); cvt := ints
            end
        end else skip([becomes,tosy,downtosy,dosy]+fsys, 2);
      if sy = becomes then
        begin insymbol; expression([tosy,downtosy,dosy]+fsys, x);
          if x.typ <> cvt then error(19);
        end else skip([tosy,downtosy,dosy]+fsys, 51);
      f = 14;
      if sy in [tosy, downtosy] then
        begin if sy = downtosy then f := 16;
          insymbol; expression([dosy]+fsys, x);
          if x.typ <> cvt then error(19)
        end else skip([dosy]+fsys, 55);
      lc1 := lc; emit(f);
      if sy = dosy then insymbol else error(54);
      lc2 := lc; statement(fsys);
      emit1(f+1,lc2); code[lc1].y := lc
    end (*forstatement*) ;

    procedure standproc(n: integer);
       var i,f: integer;
           x,y: item;
    begin
      case n of
 1,2: begin (*read*)
        if not iflag then
          begin error(20); iflag := true
          end ;
        if sy = lparent then
        begin
          repeat insymbol;
            if sy <> ident then error(2) else
            begin i := loc(id); insymbol;
              if i <> 0 then
              if tab[i].obj <> variable then error(37) else
              begin x.typ := tab[i].typ; x.ref := tab[i].ref;
                if tab[i].normal then f := 0 else f := 1;
                emit2(f, tab[i].lev, tab[i].adr);
                if sy in [lbrack,lparent,period] then
                  selector(fsys+[comma,rparent], x);
                if x.typ in [ints,reals,chars,notyp] then
                  emit1(27, ord(x.typ)) else error(40)
              end
            end ;
            test([comma,rparent], fsys, 6);
          until sy <> comma;
          if sy = rparent then insymbol else error(4)
        end ;
        if n = 2 then emit(62)
      end ;
 3,4: begin (*write*)
        if sy = lparent then
        begin
          repeat insymbol;
            if sy = string then
              begin emit1(24,sleng); emit1(28,inum); insymbol
              end else
            begin expression(fsys+[comma,colon,rparent], x);
              if not (x.typ in stantyps) then error(41);
              if sy = colon then
              begin insymbol;
                expression(fsys+[comma,colon,rparent], y);
                if y.typ <> ints then error(43);
                if sy = colon then
                begin if x.typ <> reals then error(42);
                  insymbol; expression(fsys+[comma,rparent], y)
                  if y.typ <> ints then error(43);
                  emit(37)
                end
                else emit1(30, ord(x.typ))
              end
              else emit1(29, ord(x.typ))
            end
          until sy <> comma;
          if sy = rparent then insymbol else error(4)
        end ;
        if n = 4 then emit(63)
        end ;
      end (*case*)
    end (*standproc*) ;

  begin (*statement*)
    if sy in statbegsys+[ident] then
        case sy of
          ident:    begin i := loc(id); insymbol;
                      if i <> 0 then
                      case tab[i].obj of
                        konstant, type1: error(45);
                        variable:
                            assignment(tab[i].lev, tab[i].adr);
                        prozedure:
                          if tab[i].lev <> 0 then call(fsys, i)
                                  else standproc(tab[i].adr);
                        funktion:
                          if tab[i].ref = display[level]
                            then assignment(tab[i].lev+1,0)
                            else error(45)
                      end
                    end ;
          beginsy:  compoundstatement;
          ifsy:     ifstatement;
          casesy:   casestatement;
          whilesy:  whilestatement;
          repeatsy: repeatstatement;
          forsy:    forstatement;
        end;
      test(fsys, [], 14)
  end (*statement*) ;

begin (*block*) dx := 5; prt := t;
  if level > lmax then fatal(5);
  test([lparent,colon,semicolon], fsys, 7);
  enterblock; display[level] := b; prb := b;
  tab[prt].typ := notyp; tab[prt].ref := prb;
  if sy = lparent then parameterlist;
  btab[prb].lastpar := t; btab[prb].psize := dx;
  if isfun then
    if sy = colon then
    begin insymbol;   (*function type*)
      if sy = ident then
      begin x := loc(id); insymbol;
        if x <> 0 then
          if tab[x].obj <> type1 then error(29) else
            if tab[x].typ in stantyps
              then tab[prt].typ := tab[x].typ
              else error(15)
      end else skip([semicolon]+fsys, 2)
    end else error(5);
  if sy = semicolon then insymbol else error(14);
  repeat
    if sy = constsy then constantdeclaration;
    if sy = typesy then typedeclaration;
    if sy = varsy then variabledeclaration;
    btab[prb].vsize := dx;
    while sy in [proceduresy,functionsy] do procdeclaration;
    test([beginsy], blockbegsys+statbegsys, 56)
  until sy in statbegsys;
  tab[prt].adr := lc;
  insymbol; statement([semicolon,endsy]+fsys);
  while sy in [semicolon]+statbegsys do
    begin if sy = semicolon then insymbol else error(14);
      statement([semicolon,endsy]+fsys)
    end ;
  if sy = endsy then insymbol else error(57);
  test(fsys+[period], [], 6)
end (*block*) ;

procedure interpret;
  (*global code, tab, btab*)
  var ir: order;      (*instruction buffer*}
      pc: integer;    (*program counter*)
      ps: (run,fin,caschk,divchk,inxchk,stkchk,linchk,
           lngchk,redchk);
      t:  integer;    (*top stack index*)
      b:  integer;    (*base index*)
      lncnt, ocnt, blkcnt, chrcnt: integer;     (*counters*}
      h1,h2,h3,h4: integer;
      fld: array [1..4] of integer;     (*default field widths*)

      display: array [1..lmax] of integer;
      s: array [1..stacksize] of     (*blockmark:              *)
         record case types of        (*   s[b+0] = fct result  *)
           ints:  (i: integer);      (*   s[b+1] = return adr  *)
           reals: (r: real);         (*   s[b+2] = static link *)
           bools: (b: boolean);      (*   s[b+3] = dynamic link*)
           chars: (c: char)          (*   s[b+4] = table index *)
         end ;

begin (*interpret*)
  s[1].i := 0; s[2].i := 0; s[3].i := -1; s[4].i := btab[1].last;
  b := 0; display[1] := 0;
  t := btab[2].vsize - 1; pc := tab[s[4].i].adr;
  ps := run;
  lncnt := 0; ocnt := 0; chrcnt := 0;
  fld[1] := 10; fld[2] := 22; fld[3] := 10; fld[4] := 1;
  repeat ir := code[pc]; pc := pc+1; ocnt := ocnt + 1;
    case ir.f of
  0: begin (*load address*) t := t+1;
       if t > stacksize then ps := stkchk
         else s[t].i := display[ir.x] + ir.y
     end ;
  1: begin (*load value*) t := t+1;
       if t > stacksize then ps := stkchk
         else s[t] := s[display[ir.x] + ir.y]
     end ;
  2: begin (*load indirect*) t := t+1;
       if t > stacksize then ps := stkchk
         else s[t] := s[s[display[ir.x] + ir.y].i]
     end ;
  3: begin (*update display*)
       h1 := ir.y; h2 := ir.x; h3 := b;
       repeat display[h1] := h3; h1 := h1-1; h3 := s[h3+2].i
       until h1 = h2
     end ;
  8: case ir.y of
      0: s[t].i := abs(s[t].i);
      1: s[t].r := abs(s[t].r);
      2: s[t].i := sqr(s[t].i);
      3: s[t].r := sqr(s[t].r):
      4: s[t].b := odd(s[t].i);
      5: begin (* s[t].c := chr(s[t].i); *)
           if (s[t].i < 0) or (s[t].i > 63) then ps := inxchk
         end ;
      6: (* s[t].i := ord(s[t].c) *);
      7: s[t].c := succ(s[t].c);
      8: s[t].c := pred(s[t].c);
      9: s[t].i := round(s[t].r);
     10: s[t].i := trunc(s[t].r);
     11: s[t].r := sin(s[t].r);
     12: s[t].r := cos(s[t].r);
     13: s[t].r := exp(s[t].r);
     14: s[t].r := ln(s[t].r);
     15: s[t].r := sqrt(s[t].r);
     16: s[t].r := arctan(s[t].r);
     17: begin t := t+1;
           if t > stacksize then ps = stkchk
                            else s[t].b := eos(input)
         end ;
     18: begin t := t+1;
           if t > stacksize then ps = stkchk
                            else s[t].b := eoln(input)
         end ;
     end ;
  9: s[t].i := s[t].i + ir.y;   (*offset*)
 10: pc := ir.y;  (*jump*)
 11: begin (*conditional jump*)
       if not s[t].b then pc := ir.y;  t := t-1
     end ;
 12: begin (*switch*) h1 := s[t].i; t := t-1;
       h2 := ir.y; h3 := 0;
       repeat if code[h2].f <> 13 then
                begin h3 := 1; ps := caschk
                end else
              if code[h2].y = h1 then
                begin h3 := 1; pc := code[h2+1].y
                end else
              h2 := h2 + 2
       until h3 <> 0
     end ;
 14: begin (*for1up*) h1 := s[t-1].i;
       if h1 <= s[t].i then s[s[t-2].i].i := h1 else
          begin t := t-3; pc := ir.y
          end
     end ;
 15: begin (*for2up*) h2 := s[t-2].i; h1 := s[h2].i + 1;
       if h1 <= s[t].i then
         begin s[h2].i := h1; pc := ir.y end
       else t := t-3;
     end ;
 16: begin (*for1down*) h1 := s[t-1].i;
       if h1 >= s[t].i then s[s[t-2].i].i := h1 else
          begin pc := ir.y; t := t-3
          end
     end ;
 17: begin (*for2down*) h2 := s[t-2].i; h1 := s[h2].i - 1;
       if h1 >= s[t].i then
         begin s[h2].i := h1; pc := ir.y end
       else t := t-3;
     end ;
 18: begin (*mark stack*)  h1 := btab[tab[ir.y].ref].vsize;
       if t+h1 > stacksize then ps := stkchk else
         begin t := t+5; s[t-1].i := h1-1; s[t].i := ir.y
         end
     end ;
 19: begin (*call*) h1 := t - ir.y;  (*h1 points to base*)
       h2 := s[h1+4].i;            (*h2 points to tab*)
       h3 := tab[h2].lev; display[h3+1] := h1;
       h4 := s[h1+3].i + h1;
       s[h1+1].i := pc; s[h1+2].i := display[h3]; s[h1+3].i := b;
       for h3 := t+1 to h4 do s[h3].i := 0;
       b := h1; t := h4; pc := tab[h2].adr
     end ;
 20: begin (*index1*) h1 := ir.y;      (*h1 points to atab*)
       h2 := atab[h1].low; h3 := s[t].i;
       if h3 < h2 then ps := inxchk else
       if h3 > atab[h1].high then ps := inxchk else
         begin t := t-1; s[t].i := s[t].i + (h3-h2)
         end
     end ;
 21: begin (*index*)  h1 := ir.y;     (*h1 points to atab*)
       h2 := atab[h1].low; h3 := s[t].i;
       if h3 < h2 then ps := inxchk else
       if h3 > atab[h1].high then ps := inxchk else
         begin t := t-1; s[t].i := s[t].i + (h3-h2)*atab[h1].elsize
         end
     end ;
 22: begin (*load block*) h1 := s[t].i; t := t-1;
       h2 := ir.y + t; if h2 > stacksize then ps := stkchk else
       while t < h2 do
         begin t := t+1; s[t] := s[h1]; h1 := h1+1
         end
     end ;
 23: begin (*copy block*) h1 := s[t-1].i;
       h2 := s[t].i; h3 := h1 + ir.y;
       while h1 < h3 do
         begin s[h1] := s[h2]; h1 := h1+1; h2 := h2+1
         end ;
       t := t-2
     end ;
 24: begin (*literal*) t := t+1;
       if t > stacksize then ps := stkchk else s[t].i := ir.y
     end ;
 25: begin (*load real*) t := t+1;
       if t>stacksize then ps := stkchk else s[t].r := rconst[ir.y]
     end ;
 26: begin (*float*) h1 := t - ir.y; s[h1].r := s[h1].i
     end ;
 27: begin (*read*)
       if eos(input) then ps := redchk else
          case ir.y of
           1: read(s[s[t].i].i);
           2: read(s[s[t].i].r);
           4: read(s[s[t].i].c);
          end ;
       t := t-1
     end ;
 28: begin (*write string*)
       h1 := s[t].i; h2 := ir.y; t := t-1;
       chrcnt := chrcnt+h1; if chrcnt > lineleng then ps := lngchk;
       repeat write(stab[h2]); h1 := h1-1; h2 := h2+1
       until h1 = 0
     end ;
 29: begin (*write1*)
       chrcnt := chrcnt + fld[ir.y];
       if chrcnt > lineleng then ps := lngchk else
       case ir.y of
        1: write(s[t].i: fld[1]);
        2: write(s[t].r: fld[2]);
        3: write(s[t].b: fld[3]);
        4: write(s[t].c);
       end ;
       t := t-1
     end ;
 30: begin (*write2*)
       chrcnt := chrcnt + s[t].i;
       if chrcnt > lineleng then ps := lngchk else
       case ir.y of
        1: write(s[t-1].i: s[t].i);
        2: write(s[t-1].r: s[t].i);
        3: write(s[t-1].b: s[t].i);
        4: write(s[t-1].c: s[t].i);
       end ;
       t := t-2
     end ;
 31: ps := fin;
 32: begin (*exit procedure*)
       t := b-1; pc := s[b+1].i; b := s[b+3].i
     end ;
 33: begin (*exit function*)
       t := b; pc := s[b+1].i; b := s[b+3].i
     end ;
 34: s[t] := s[s[t].i];
 35: s[t].b := not s[t].b;
 36: s[t].i := - s[t].i;
 37: begin chrcnt := chrcnt + s[t-1].i;
       if chrcnt > lineleng then ps := lngchk else
          write(s[t-2].r: s[t-1].i: s[t].i);
       t := t-3
     end ;
 38: begin (*store*) s[s[t-1].i] := s[t]; t := t-2
     end ;
 39: begin t := t-1; s[t].b := s[t].r = s[t+1].r
     end ;
 40: begin t := t-1; s[t].b := s[t].r <> s[t+1].r
     end ;
 41: begin t := t-1; s[t].b := s[t].r < s[t+1].r
     end ;
 42: begin t := t-1; s[t].b := s[t].r <= s[t+1].r
     end ;
 43: begin t := t-1; s[t].b := s[t].r > s[t+1].r
     end ;
 44: begin t := t-1; s[t].b := s[t].r >= s[t+1].r
     end ;
 45: begin t := t-1; s[t].b := s[t].i = s[t+1].i
     end ;
 46: begin t := t-1; s[t].b := s[t].i <> s[t+1].i
     end ;
 47: begin t := t-1; s[t].b := s[t].i < s[t+1].i
     end ;
 48: begin t := t-1; s[t].b := s[t].i <= s[t+1].i
     end ;
 49: begin t := t-1; s[t].b := s[t].i > s[t+1].i
     end ;
 50: begin t := t-1; s[t].b := s[t].i >= s[t+1].i
     end ;
 51: begin t := t-1; s[t].b := s[t].b or s[t+1].b
     end ;
 52: begin t := t-1; s[t].i := s[t].i + s[t+1].i
     end ;
 53: begin t := t-1; s[t].i := s[t].i - s[t+1].i
     end ;
 54: begin t := t-1; s[t].r := s[t].r + s[t+1].r;
     end ;
 55: begin t := t-1; s[t].r := s[t].r - s[t+1].r;
     end ;
 56: begin t := t-1; s[t].b := s[t].b and s[t+1].b
     end ;
 57: begin t := t-1; s[t].i := s[t].i * s[t+1].i
     end ;
 58: begin t := t-1;
       if s[t+1].i = 0 then ps := divchk else
         s[t].i := s[t].i div s[t+1].i
     end ;
 59: begin t := t-1;
       if s[t+1].i = 0 then ps := divchk else
         s[t].i := s[t].i mod s[t+1].i
     end ;
 60: begin t := t-1; s[t].r := s[t].r * s[t+1].r;
     end;
 61: begin t := t-1; s[t].r := s[t].r / s[t+1].r;
     end ;
 62: if eos(input) then ps := redchk else readln;
 63: begin writeln; lncnt := lncnt + 1; chrcnt := 0;
        if lncnt > linelimit then ps := linchk
     end
    end (*case*) ;
  until ps <> run;

  if ps <> fin then
  begin writeln;
    write('0halt at', pc:5, ' because of ');
    case ps of
      caschk: writeln('undefined case');
      divchk: writeln('division by 0');
      inxchk: writeln('invalid index');
      stkchk: writeln('storage overflow');
      linchk: writeln('too much output');
      lngchk: writeln('line too long');
      redchk: writeln('reading past end of file');
    end ;
    h1 := b; blkcnt := 10;   (*post mortem dump*)
    repeat writeln; blkcnt := blkcnt - 1;
      if blkcnt = 0 then h1 := 0; h2 := s[h1+4].i;
      if h1<>0 then
        writeln(' ', tab[h2].name, ' called at', s[h1+1].i: 5);
      h2 := btab[tab[h2].ref].last;
      while h2 <> 0 do
      with tab[h2] do
      begin if obj = variable then
            if typ in stantyps then
            begin write('    ', name, ' = ');
              if normal then h3 := h1+adr else h3 := s[h1+adr].i;
              case typ of
               ints:  writeln(s[h3].i);
               reals: writeln(s[h3].r);
               bools: writeln(s[h3].b);
               chars: writeln(s[h3].c);
              end
            end ;
            h2 := link
      end ;
      h1 := s[h1+3].i
    until h1 < 0;
  end ;
  writeln; writeln(ocnt, ' steps')
end (*interpret*) ;

begin writeln;   {main program}
   key[ 1] := 'and       '; key[ 2] := 'array     ';
   key[ 3] := 'begin     '; key[ 4] := 'case      ';
   key[ 5] := 'const     '; key[ 6] := 'div       ';
   key[ 7] := 'downto    '; key[ 8] := 'do        ';
   key[ 9] := 'else      '; key[10] := 'end       ';
   key[11] := 'for       '; key[12] := 'function  ';
   key[13] := 'if        '; key[14] := 'mod       ';
   key[15] := 'not       '; key[16] := 'of        ';
   key[17] := 'or        '; key[18] := 'procedure ';
   key[19] := 'program   '; key[20] := 'record    ';
   key[21] := 'repeat    '; key[22] := 'then      ';
   key[23] := 'to        '; key[24] := 'type      ';
   key[25] := 'until     '; key[26] := 'var       ';
   key[27] := 'while     ';
   ksy[ 1] := andsy;        ksy[ 2] := arraysy;
   ksy[ 3] := beginsy;      ksy[ 4] := casesy;
   ksy[ 5] := constsy;      ksy[ 6] := idiv;
   ksy[ 7] := downtosy;     ksy[ 8] := dosy;
   ksy[ 9] := elsesy;       ksy[10] := endsy;
   ksy[11] := forsy;        ksy[12] := functionsy;
   ksy[13] := ifsy;         ksy[14] := imod;
   ksy[15] := notsy;        ksy[16] := ofsy;
   ksy[17] := orsy;         ksy[18] := proceduresy;
   ksy[19] := programsy;    ksy[20] := recordsy;
   ksy[21] := repeatsy;     ksy[22] := thensy;
   ksy[23] := tosy;         ksy[24] := typesy;
   ksy[25] := untilsy;      ksy[26] := varsy;
   ksy[27] := whilesy;
   sps['+'] := plus;        sps['-'] := minus;
   sps['*'] := times;       sps['/'] := rdiv;
   sps['('] := lparent;     sps[')'] := rparent;
   sps['='] := eql;         sps[','] := comma;
   sps['['] := lbrack;      sps[']'] := rbrack;
   sps['#'] := neq;         sps['&'] := andsy;
   sps[';'] := semicolon;
  constbegsys := [plus,minus,intcon,realcon,charcon,ident];
  typebegsys := [ident,arraysy,recordsy];
  blockbegsys := [constsy,typesy,varsy,proceduresy,
                  functionsy,beginsy];
  facbegsys := [intcon,realcon,charcon,ident,lparent,notsy];
  statbegsys := [beginsy,ifsy,whilesy,repeatsy,forsy,casesy];
  stantyps := [notyp,ints,reals,bools,chars];
  lc := 0; ll := 0; cc := 0; ch := ' ';
  errpos := 0; errs := []; insymbol;
  t := -1; a := 0; b := 1; sx := 0; c2 := 0;
  display[0] := 1;
  iflag := false; oflag := false;
  if sy <> programsy then error(3) else
  begin insymbol;
    if sy <> ident then error(2) else
    begin progname := id; insymbol;
      if sy <> lparent then error(9) else
      repeat insymbol;
        if sy <> ident then error(2) else
        begin if id = 'input     ' then iflag := true else
              if id = 'output    ' then oflag := true else error(0);
           insymbol
        end
      until sy <> comma;
      if sy = rparent then insymbol else error(4);
      if not oflag then error(20)
    end
  end ;
  enter('          ', variable, notyp, 0);  (*sentinel*)
  enter('false     ', konstant, bools, 0);
  enter('true      ', konstant, bools, 1);
  enter('real      ', type1, reals, 1);
  enter('char      ', type1, chars, 1);
  enter('boolean   ', type1, bools, 1);
  enter('integer   ', type1, ints , 1);
  enter('abs       ', funktion, reals,0);
  enter('sqr       ', funktion, reals,2);
  enter('odd       ', funktion, bools,4);
  enter('chr       ', funktion, chars,5);
  enter('ord       ', funktion, ints, 6);
  enter('succ      ', funktion, chars,7);
  enter('pred      ', funktion, chars,8);
  enter('round     ', funktion, ints, 9);
  enter('trunc     ', funktion, ints, 10);
  enter('sin       ', funktion, reals, 11);
  enter('cos       ', funktion, reals, 12);
  enter('exp       ', funktion, reals, 13);
  enter('ln        ', funktion, reals, 14);
  enter('sqrt      ', funktion, reals, 15);
  enter('arctan    ', funktion, reals, 16);
  enter('eof       ', funktion, bools, 17);
  enter('eoln      ', funktion, bools, 18);
  enter('read      ', prozedure, notyp, 1);
  enter('readln    ', prozedure, notyp, 2);
  enter('write     ', prozedure, notyp, 3);
  enter('writeln   ', prozedure, notyp, 4);
  enter('          ', prozedure, notyp, 0);
  with btab[1] do
    begin last := t; lastpar := 1; psize := 0; vsize := 0
    end ;

  block(blockbegsys+statbegsys, false, 1);
  if sy <> period then error(22);
  emit(31);  (*halt*)
  if btab[2].vsize > stacksize then error(49);
  if progname = 'test0     ' then printtables;

  if errs = [] then
  begin
    if iflag then
    begin getseg(input);
      if eof(input) then writeln(' input data missing') else
      begin writeln(' (eor)'); (*copy input data*)
        while not eos(input) do
        begin write(' ');
          while not eoln(input) do
            begin read(ch); write(ch)
            end ;
          writeln; read(ch)
        end ;
        getseg(input,0)
      end
    end ;
    writeln(' (eof)');
    interpret
  end ;
  else errormsg;
99:
end.