Re: Tiny-Pascal & People's Pascal (A Johnstone)
21 Jul 1999 00:16:59 -0400

          From comp.compilers

Related articles
Tiny-Pascal & People's Pascal (Ronald Praver) (1999-07-14)
Re: Tiny-Pascal & People's Pascal (Bill Fahle) (1999-07-20)
Re: Tiny-Pascal & People's Pascal (1999-07-21)
Re: Tiny-Pascal & People's Pascal (Sammy Mitchell) (1999-07-21)
Re: Tiny-Pascal & People's Pascal (Peter Zechmeister) (1999-07-23)
Re: Tiny-Pascal & People's Pascal (Juergen Kahrs) (1999-07-23)
| List of all articles for this month |

From: (A Johnstone)
Newsgroups: comp.compilers
Date: 21 Jul 1999 00:16:59 -0400
Organization: Royal Holloway, University of London
References: 99-07-048 99-07-092
Keywords: Pascal

Probably the moderator will trim this, but enclosed is the full source
for Pascal-S from Wirth's 1970's paper. Many people have built systems around
this program. You can also get it from my ftp server:


  This version is set up to compile with Turbo-C. A word of warning to
  people using the original paper: Wirth uses an array of keywords in
  alphabetical order that is searched using a binary search. The
  character collation sequence on the CDC6600 is not the same as for
  ASCII, so the table needs reordering so that DO comes before DOWNTO
  (on CDC space > W).

[A whole Pascal compiler in one mail message? Who could resist! -John]

  -- Pascal-S follows --
{ Pascal-S from N Wirth's paper 'Pascal-S: a subset and its implementation'
    which is most easily found in the book 'Pascal: the language and its
    implementation' edited by Baron. You migtht also like to look at
    'Principles of concurrent programming' by Ben-Ari (the first edition)
    which contains a munged version of Pascal-S that supports some

{ This version of Pascal-S was originally fetched from
    where it lived in directory /jan. I believe that it was set up by Jan van
    de Snepscheut. I don't know anything else about its provenance. I modified
    the program to suit Turbo Pascal version 5.5 as detailed in the next
    comment. Jan's fixes to the published program are detailed in the comment
    after that.

                                                          Adrian Johnstone, 22 March 1995

{For Turbo Pascal:
      changed string to sstring
      changed halt to hhalt
      changed getch to read from infile instead of stdin and added file assign
      statements to mainline routine.
      removed label 99:
      changed 'goto 99' to halt;
      added chr(10) and chr(13) to list of throw-aways in getsym

{ line 295 (counting from 1 starting at program PascalS) is
                                                                    gen1(mulc, ttab[t].size); gen0(add)
    whereas the version printed in the book accidentally reads
                                                                    gen1(mulc, ttab[t].size)
    the present version also implements boolean negation

    the procedure funcdeclaration in the version printed in the book is
    erroneous. The first line on page 376 in the book should read
                                                                    if lev>1 then dx:=-1
    the last line of the procedure should read
                gen1(exit,itab[f].resultadr-dx); lev:=lev-1; dx:=odx

program PascalS(infile, output);

const cxmax = 2000; { size of code array }
            amax = 16383; { maximum address }

type opcode = (add, neg, mul, divd, remd, div2, rem2, eqli, neqi, lssi,
                                leqi, gtri, geqi, dupl, swap, andb, orb,
                                load, stor, hhalt, wri, wrc, wrl, rdi, rdc, rdl, eol,
                                ldc, ldla, ldl, ldg, stl, stg, move, copy, addc, mulc,
                                jump, jumpz, call, adjs, sets, exit);
            instr = record case op: opcode of
                                  add, neg, mul, divd, remd, div2, rem2, eqli, neqi, lssi,
                                  leqi, gtri, geqi, dupl, swap, andb, orb,
                                  load, stor, hhalt, wri, wrc, wrl, rdi, rdc, rdl, eol:
                                  ldc, ldla, ldl, ldg, stl, stg, move, copy, addc, mulc,
                                  jump, jumpz, call, adjs, sets, exit:
                                                (a: integer)

var code: array [0..cxmax] of instr;
        m : array [0..amax] of integer;
        infile: text;

procedure compile;

const imax = 100; { length of identifier table }
            tmax = 100; { length of type table }
            lmax = 10; { maximum level }
            al = 10; { length of identifiers }
            fabs = 0; { standard functions }
            fsqr = 1; fodd = 2; fchr = 3;
            ford = 4; fwrite = 5; fwriteln= 6;
            fread = 7; freadln= 8; feoln = 9;
            { standard types }
            intip = 1; booltip= 2; chartip = 3;

type symbol = (ident, number, sstring, plus, minus, star, lbrack, rbrack,
                              colon, eql, neq, lss, leq, gtr, geq, lparen, rparen, comma,
                              semicolon, period, becomes,
                              beginsym, endsym, ifsym, thensym, elsesym, whilesym, dosym,
                              casesym, repeatsym, untilsym, forsym, tosym, downtosym,
                              notsym, divsym, modsym, andsym, orsym, constsym, varsym,
                              typesym, arraysym, ofsym, recordsym, progsym, funcsym,
          idkind = (konst, varbl, field, tipe, funkt);
          tpkind = (simple, arrays, records);
          alfa = packed array [] of char;

var ch: char; { last character read }
        cc: integer; { character count }
        ll: integer; { line length }
        line: array [1..81] of char;{ present input line }
        sym: symbol; { last symbol read }
        id: alfa; { last identifier read }
        num: integer; { last number read }
        str: array [1..80] of char; { last string read }
        slen: integer; { length of last string }
        word: array [beginsym..procsym] of alfa;
        cx: integer; { code index }
        lev: integer; { procedure nesting level }
        dx: integer; { offset in stack }
        labeled: boolean; { next instruction has label }
        namelist: array [-1..lmax] of integer;
        ix, tx: integer; { indices in tables }
        itab: array [0..imax] of { identifier table }
                        record name: alfa; link: integer; tip: integer;
                            case kind: idkind of
                                konst: (val: integer);
                                varbl: (vlevel, vadr: integer; refpar: boolean);
                                field: (offset: integer);
                                tipe : ();
                                funkt: (flevel, fadr, lastpar, resultadr: integer;
                                                      inside: boolean)
        ttab: array [1..tmax] of { type table }
                        record size: integer;
                            case kind: tpkind of
                                simple : ();
                                arrays : (low, high, elemtip: integer);
                                records: (fields: integer)

procedure error(n: integer);
    var i: integer;
begin for i:= 1 to ll do write(line[i]); writeln;
            for i:= 1 to cc-2 do write(' '); writeln('^');
            writeln('error ', n:1, ' detected');
            halt; { Turbo Pascal exit routine }

procedure getch;
begin if cc=ll then begin
                    if eof(infile) then error(100); ll:= 0; cc:= 0;
                    while not eoln(infile) do begin ll:= ll+1; read(infile, line[ll]) end;
                    ll:= ll+1; read(infile, line[ll])
            cc:= cc+1; ch:= line[cc]

procedure getsym;
    var k: integer; s: symbol; strend: boolean;
begin while ch in [' ', chr(9), chr(13), chr(10)] do getch;
            if ch in ['a'..'z', 'A'..'Z'] then begin
                    k:= 0;
                    repeat if k<>al then begin k:= k+1; id[k]:= ch end;
                    until not (ch in ['a'..'z', 'A'..'Z', '0'..'9']);
                    while k<>al do begin k:= k+1; id[k]:= ' ' end;
                    sym:= ident;
                    for s:= beginsym to procsym do if word[s]=id then sym:= s
            end else if ch in ['0'..'9'] then begin
                    num:= 0; sym:= number;
                    repeat num:= num*10 + (ord(ch)-ord('0'));
                    until not (ch in ['0'..'9'])
            end else if ch=':' then begin
                    if ch='=' then begin getch; sym:= becomes end
                                        else sym:= colon
            end else if ch='>' then begin
                    if ch='=' then begin getch; sym:= geq end
                                        else sym:= gtr
            end else if ch='<' then begin
                    if ch='=' then begin getch; sym:= leq end else
                    if ch='>' then begin getch; sym:= neq end
                                        else sym:= lss
            end else if ch='.' then begin
                    if ch='.' then begin getch; sym:= colon end
                                        else sym:= period
            end else if ch='''' then begin
                    slen:= 0; strend:= false; sym:= sstring;
                    repeat if cc=ll then error(101); getch;
                                  if ch='''' then begin
                                          if ch='''' then begin
                                                  slen:= slen+1; str[slen]:= ch
                                          end else
                                                  strend:= true
                                  end else begin
                                          slen:= slen+1; str[slen]:= ch
                    until strend;
                    if slen=0 then error(102)
            else if ch='+' then begin getch; sym:= plus end
            else if ch='-' then begin getch; sym:= minus end
            else if ch='*' then begin getch; sym:= star end
            else if ch='(' then begin getch; sym:= lparen end
            else if ch=')' then begin getch; sym:= rparen end
            else if ch='[' then begin getch; sym:= lbrack end
            else if ch=']' then begin getch; sym:= rbrack end
            else if ch='=' then begin getch; sym:= eql end
            else if ch=',' then begin getch; sym:= comma end
            else if ch=';' then begin getch; sym:= semicolon end
            else if ch='{'
            then begin repeat getch until ch='}';
                                  getch; getsym
            else error(103)

procedure check(s: symbol);
begin if sym<>s then error(ord(s)) end;

procedure skip(s: symbol);
begin check(s); getsym end;

procedure enter(id: alfa; k: idkind; t: integer);
    var j: integer;
begin if ix=imax then error(104); ix:= ix+1;
            itab[0].name:= id; j:= namelist[lev];
            while itab[j].name<>id do j:= itab[j].link;
            if j<>0 then error(105);
            with itab[ix] do begin
                name:= id; link:= namelist[lev]; tip:= t; kind:= k
            namelist[lev]:= ix

function position: integer;
    var i, j: integer;
begin itab[0].name:= id; i:= lev;
            repeat j:= namelist[i];
                          while itab[j].name<>id do j:= itab[j].link;
                          i:= i-1
            until (i<-1) or (j<>0);
            if j=0 then error(106); position:= j

procedure gen(i: instr);
begin case i.op of
                dupl, eol, ldc, ldla, ldl, ldg:
                    dx:= dx-1;
                neg, div2, rem2, swap, load, hhalt, wrl, rdl,
                addc, mulc, jump, call, sets, exit:
                add, mul, divd, remd, eqli, neqi, lssi, leqi, gtri,
                geqi, andb, orb, wrc, rdi, rdc, stl, stg, jumpz:
                    dx:= dx+1;
                stor, wri, move:
                    dx:= dx+2;
                    dx:= dx-i.a+1;
                    dx:= dx+i.a
            if not (((i.op in [addc, adjs]) and (i.a=0)) or
                            ((i.op=mulc) and (i.a=1))) then
            if labeled then begin
                    code[cx]:= i; cx:= cx+1; labeled:= false
            end else if (code[cx-1].op=ldc) and (i.op=add) then
                    code[cx-1].op:= addc
            else if (code[cx-1].op=ldc) and (i.op=mul) then
                    code[cx-1].op:= mulc
            else if (code[cx-1].op=ldc) and (i.op=neg) then
                    code[cx-1].a:= -code[cx-1].a
            else if (code[cx-1].op=ldc) and (code[cx-1].a=2) and (i.op=divd) then
                    code[cx-1].op:= div2
            else if (code[cx-1].op=ldc) and (code[cx-1].a=2) and (i.op=remd) then
                    code[cx-1].op:= rem2
            else if (code[cx-1].op=ldc) and (i.op=stor) then
                    code[cx-1].op:= stg
            else if (code[cx-1].op=ldc) and (i.op=load) then
                    code[cx-1].op:= ldg
            else if (code[cx-1].op=ldla) and (i.op=stor) then
                    code[cx-1].op:= stl
            else if (code[cx-1].op=ldla) and (i.op=load) then
                    code[cx-1].op:= ldl
            else begin
                    code[cx]:= i; cx:= cx+1
end end;

procedure gen0(op: opcode);
    var i: instr;
begin i.op:= op; gen(i) end;

procedure gen1(op: opcode; a: integer);
    var i: instr;
begin i.op:= op; i.a:= a; gen(i) end;

function codelabel: integer;
begin codelabel:= cx; labeled:= true end;

procedure address(lv, ad: integer);
begin if lv=0 then
                    gen1(ldc, ad)
            else if lv=lev then
                    gen1(ldla, ad-dx)
            else begin
                    gen1(ldl, -dx);
                    while lv+1<>lev do begin gen0(load); lv:= lv+1 end;
                    gen1(addc, ad)
end end;

procedure addressvar(ref: integer);
begin with itab[ref] do
            begin address(vlevel, vadr); if refpar then gen0(load) end

procedure mustbe(x, y: integer);
begin if x<>y then
            if (ttab[x].kind=arrays) and (ttab[y].kind=arrays) and
                  (ttab[x].low=ttab[y].low) and (ttab[x].high=ttab[y].high)
            then mustbe(ttab[x].elemtip, ttab[y].elemtip)
            else error(107)

procedure expression(var x: integer);

procedure selector(var t: integer; var ref: integer);
    var j, x: integer;
begin t:= itab[ref].tip; getsym;
            if sym in [period, lbrack] then begin
                    addressvar(ref); ref:= 0;
                    while sym in [period, lbrack] do
                    case sym of
                        period : begin if ttab[t].kind<>records then error(108);
                                                      getsym; check(ident);
                                                      j:= ttab[t].fields; itab[0].name:= id;
                                                      while itab[j].name<>id do j:= itab[j].link;
                                                      if j=0 then error(109);
                                                      gen1(addc, itab[j].offset);
                                                      t:= itab[j].tip; getsym
                        lbrack : begin repeat if ttab[t].kind<>arrays then error(110);
                                                                    getsym; expression(x); mustbe(intip, x);
                                                                    gen1(addc, -ttab[t].low);
                                                                    t:= ttab[t].elemtip;
                                                                    gen1(mulc, ttab[t].size); gen0(add)
                                                      until sym<>comma;
end end end end;

procedure varpar(var t: integer);
    var j: integer;
begin check(ident); j:= position; selector(t, j);
            if j<>0 then addressvar(j)

procedure standfct(n: integer);
    var x, l: integer;
begin case n of
                fabs: begin skip(lparen); expression(x); mustbe(intip, x);
                                    gen0(dupl); gen1(ldc, 0); gen0(lssi);
                                    l:= codelabel; gen1(jumpz, 0); gen0(neg);
                                    code[l].a:= codelabel;
                fsqr: begin skip(lparen); expression(x); mustbe(intip, x);
                                    gen0(dupl); gen0(mul); skip(rparen)
                fodd: begin skip(lparen); expression(x); mustbe(intip, x);
                                    gen0(rem2); skip(rparen)
                fchr: begin skip(lparen); expression(x); mustbe(intip, x);
                ford: begin skip(lparen); expression(x); mustbe(chartip, x);
                fwrite, fwriteln:
                            begin if n=fwrite then check(lparen);
                                    if sym=lparen then begin
                                            repeat getsym;
                                                    if sym=sstring then begin
                                                            for x:= 1 to slen do begin
                                                                    gen1(ldc, ord(str[x]));
                                                    end else begin
                                                            if sym=colon then begin
                                                                    mustbe(intip, x); getsym;
                                                                    expression(x); mustbe(intip,x);
                                                            end else if x=intip then begin
                                                                    gen1(ldc, 8); gen0(wri)
                                                            end else if x=chartip then
                                            until sym<>comma;
                                    if n=fwriteln then gen0(wrl)
          fread, freadln:
                            begin if n=fread then check(lparen);
                                    if sym=lparen then begin
                                            repeat getsym; varpar(x);
                                                          if x=intip then gen0(rdi) else
                                                          if x=chartip then gen0(rdc)
                                                                                    else error(112)
                                            until sym<>comma;
                                    if n=freadln then gen0(rdl)
                feoln: gen0(eol)
end end;

procedure funcall(i: integer);
    var d, p, x: integer;
begin getsym;
            with itab[i] do
            if flevel<0 then
            else begin
if tip<>0 then gen1(ldc, 0); p:= i; d:= dx;
                    if sym=lparen then begin
repeat getsym;
                                    if p=lastpar then error(113); p:= p+1;
                                    if itab[p].refpar then
                                    else begin
                                            if ttab[x].kind<>simple then gen1(copy, ttab[x].size)
                                    mustbe(itab[p].tip, x)
                            until sym<>comma;
                    if p<>lastpar then error(114);
                    if flevel<>0 then address(flevel, 0);
                    gen1(call, fadr); dx:= d
end end;

procedure factor(var t: integer);
      var i: integer;
begin if sym=ident then begin
                    i:= position; t:= itab[i].tip;
                    case itab[i].kind of
                        konst: begin getsym; gen1(ldc, itab[i].val) end;
                        varbl: begin selector(t, i);
                                                  if i<>0 then addressvar(i);
                                                  if ttab[t].kind=simple then gen0(load)
                        funkt: if t=0 then error(115) else funcall(i);
                        tipe : error(116)
            end else if sym=number then begin
                    gen1(ldc, num); t:= intip; getsym
            end else if (sym=sstring) and (slen=1) then begin
                    gen1(ldc, ord(str[1])); t:= chartip; getsym
            end else if sym=lparen then begin
                    getsym; expression(t); skip(rparen)
            end else if sym=notsym then begin
                    getsym; factor(t); mustbe(booltip, t); gen0(neg); gen1(addc, 1)
            end else

procedure term(var x: integer);
    var y: integer;
begin factor(x);
            while sym in [andsym, star, divsym, modsym] do begin
                    if sym=andsym then mustbe(booltip, x) else mustbe(intip, x);
                    case sym of
                        star : begin getsym; factor(y); gen0(mul) end;
                        divsym: begin getsym; factor(y); gen0(divd) end;
                        modsym: begin getsym; factor(y); gen0(remd) end;
                        andsym: begin getsym; factor(y); gen0(andb) end
                    mustbe(x, y)
end end;

procedure simplexpression(var x: integer);
    var y: integer;
begin if sym=plus then begin
                    getsym; term(x); mustbe(intip, x)
            end else if sym=minus then begin
                    getsym; term(x); mustbe(intip, x); gen0(neg)
            end else
            while sym in [orsym, plus, minus] do begin
                    if sym=orsym then mustbe(booltip, x) else mustbe(intip, x);
                    case sym of
                        plus : begin getsym; term(y); gen0(add) end;
                        minus: begin getsym; term(y); gen0(neg); gen0(add) end;
                        orsym: begin getsym; term(y); gen0(orb) end
                    mustbe(x, y)
end end;

procedure expression{var x: integer};
    var op: symbol; y: integer;
begin simplexpression(x);
            if sym in [eql, neq, lss, leq, gtr, geq] then begin
                    if ttab[x].kind<>simple then error(118);
                    op:= sym; getsym; simplexpression(y); mustbe(x, y);
                    case op of
                        eql: gen0(eqli);
                        neq: gen0(neqi);
                        lss: gen0(lssi);
                        leq: gen0(leqi);
                        gtr: gen0(gtri);
                        geq: gen0(geqi)
                    x:= booltip
end end;

procedure statement;
    var i, j, t, x: integer;
begin if sym=ident then begin
                    i:= position;
                    with itab[i] do
                    case kind of
                        varbl: begin selector(t, i); skip(becomes);
                                                  expression(x); mustbe(t, x);
                                                  if i=0 then gen0(swap)
                                                                else addressvar(i);
                                                  if ttab[t].kind=simple
                                                  then gen0(stor)
                                                  else gen1(move, ttab[t].size)
                        funkt: if tip=0 then
                                      else begin
if not inside then error(119);
                                              getsym; skip(becomes);
                                              expression(x); mustbe(tip, x);
                                              address(flevel+1, resultadr);
                        konst, field, tipe: error(120)
            end else if sym=ifsym then begin
                    getsym; expression(t); mustbe(booltip, t); skip(thensym);
                    i:= codelabel; gen1(jumpz, 0); statement;
                    if sym=elsesym then begin
getsym; j:= codelabel; gen1(jump, 0);
                            code[i].a:= codelabel; i:= j; statement
                    code[i].a:= codelabel
            end else if sym=whilesym then begin
                    getsym; i:= codelabel; expression(t); mustbe(booltip, t);
                    skip(dosym); j:= codelabel; gen1(jumpz, 0);
                    statement; gen1(jump, i);
                    code[j].a:= codelabel
            end else if sym=repeatsym then begin
                    i:= codelabel;
                    repeat getsym; statement until sym<>semicolon;
                    skip(untilsym); expression(t); mustbe(booltip, t);
                    gen1(jumpz, i)
            end else if sym=beginsym then begin
                    repeat getsym; statement until sym<>semicolon;
end end;

procedure block(l: integer);

procedure constant(var c, t: integer);
    var i, s: integer;
begin if (sym=sstring) and (slen=1) then begin
                    c:= ord(str[1]); t:= chartip
            end else begin
                    if sym=plus then begin getsym; s:= +1 end else
                    if sym=minus then begin getsym; s:= -1 end
                                              else s:= 0;
                    if sym=ident then begin
                            i:= position;
                            if itab[i].kind<>konst then error(121);
                            c:= itab[i].val; t:= itab[i].tip
                    end else if sym=number then begin
                            c:= num; t:= intip
                    end else
                    if s<>0 then begin mustbe(t, intip); c:= c*s end

procedure constdeclaration;
    var a: alfa; t, c: integer;
begin a:= id; getsym; skip(eql); constant(c, t);
            skip(semicolon); enter(a, konst, t); itab[ix].val:= c

procedure typ(var t: integer);
    var i, j, sz, ft: integer;
    procedure arraytyp(var t: integer);
        var x: integer;
    begin with ttab[t] do begin
                        kind:= arrays; getsym; constant(low, x); mustbe(intip, x);
                        skip(colon); constant(high, x); mustbe(intip, x);
                        if low>high then error(123);
                        if sym=comma then
                        else begin
skip(rbrack); skip(ofsym); typ(elemtip)
                        size:= (high-low+1)*ttab[elemtip].size
    end end;
begin if sym=ident then begin
                    i:= position; if itab[i].kind<>tipe then error(124);
                    t:= itab[i].tip; getsym
            end else begin
                    if tx=tmax then error(125); tx:= tx+1; t:= tx;
                    if sym=arraysym then begin
                            getsym; check(lbrack); arraytyp(t)
                    end else begin
                            if lev=lmax then error(126); lev:= lev+1;
                            namelist[lev]:= 0; check(ident); sz:= 0;
                            repeat enter(id, field, 0); i:= ix; getsym;
                                          while sym=comma do begin
getsym; check(ident); enter(id, field, 0);
                                          j:= ix; skip(colon); typ(ft);
                                          repeat itab[i].tip:= ft; itab[i].offset:= sz;
                                                        sz:= sz+ttab[ft].size; i:= i+1
                                          until i>j;
                                        if sym=semicolon then getsym else check(endsym)
                            until sym<>ident;
                            ttab[t].size:= sz; ttab[t].kind:= records;
                            ttab[t].fields:= namelist[lev]; lev:= lev-1;
end end end;

procedure typedeclaration;
    var a: alfa; t: integer;
begin a:= id; getsym; skip(eql); typ(t); skip(semicolon);
            enter(a, tipe, t)

procedure vardeclaration;
    var p, q, t: integer;
begin enter(id, varbl, 0); p:= ix; getsym;
            while sym=comma do begin
                    getsym; check(ident); enter(id, varbl, 0); getsym
            q:= ix; skip(colon); typ(t); skip(semicolon);
            repeat with itab[p] do begin
vlevel:= lev; dx:= dx-ttab[t].size; tip:= t;
                                  vadr:= dx; refpar:= false
                          p:= p+1
            until p>q

procedure funcdeclaration(isf: boolean);
    var f, p, ps, odx: integer;
    procedure paramlist;
        var r: boolean; t: integer;
    begin if sym=varsym then begin r:= true; getsym end else r:= false;
                check(ident); p:= ix; enter(id, varbl, 0); getsym;
                while sym=comma do begin
                        getsym; check(ident); enter(id, varbl, 0); getsym
                skip(colon); check(ident); typ(t);
                while p<ix do begin
                        p:= p+1; itab[p].tip:= t; itab[p].refpar:= r;
                        if r then ps:= ps+1 else ps:= ps+ttab[t].size
    end end;
begin getsym; check(ident); enter(id, funkt, 0); getsym; f:= ix;
            itab[f].flevel:= lev; itab[f].fadr:= codelabel; gen1(jump, 0);
            if lev=lmax then error(127); lev:= lev+1; namelist[lev]:= 0;
            ps:= 1; odx:= dx;
            if sym=lparen then begin
                    repeat getsym; paramlist until sym<>semicolon;
            if lev>1 then dx:= -1
                              else dx:= 0;
            itab[f].resultadr:= ps; p:= f;
            while p<ix do begin
                    p:= p+1;
                    with itab[p] do begin
                            if refpar then ps:= ps-1 else ps:= ps-ttab[tip].size;
                            vlevel:= lev; vadr:= ps
            end end;
            if isf then begin
                    skip(colon); check(ident); typ(itab[f].tip);
                    if ttab[itab[f].tip].kind<>simple then error(128)
            itab[f].lastpar:= ix; itab[f].inside:= true;
            itab[f].inside:= false;
            gen1(exit, itab[f].resultadr-dx);
            lev:= lev-1; dx:= odx;

procedure block{l: integer};
    var d, odx, oix: integer;
begin odx:= dx; oix:= ix;
            if sym=constsym then begin
                    getsym; check(ident);
                    repeat constdeclaration until sym<>ident
            if sym=typesym then begin
                    getsym; check(ident);
                    repeat typedeclaration until sym<>ident
            if sym=varsym then begin
                    getsym; check(ident);
                    repeat vardeclaration until sym<>ident
            while sym in [funcsym, procsym] do funcdeclaration(sym=funcsym);
            if l+1=codelabel then cx:= cx-1 else code[l].a:= codelabel;
            if lev=0 then
                    gen1(sets, dx)
            else begin
                    d:= dx-odx; dx:= odx; gen1(adjs, d)
            if lev<>0 then gen1(adjs, odx-dx); ix:= oix

procedure listcode;
    var i: integer;
begin for i:= 0 to cx-1 do begin
                    write(i, ' : ');
                    case code[i].op of
                        add : writeln('add');
                        neg : writeln('neg');
                        mul : writeln('mul');
                        divd : writeln('divd');
                        remd : writeln('remd');
                        div2 : writeln('div2');
                        rem2 : writeln('rem2');
                        eqli : writeln('eqli');
                        neqi : writeln('neqi');
                        lssi : writeln('lssi');
                        leqi : writeln('leqi');
                        gtri : writeln('gtri');
                        geqi : writeln('geqi');
                        dupl : writeln('dupl');
                        swap : writeln('swap');
                        andb : writeln('andb');
                        orb : writeln('orb');
                        load : writeln('load');
                        stor : writeln('stor');
                        hhalt : writeln('hhalt');
                        wri : writeln('wri');
                        wrc : writeln('wrc');
                        wrl : writeln('wrl');
                        rdi : writeln('rdi');
                        rdc : writeln('rdc');
                        rdl : writeln('rdl');
                        eol : writeln('eol');
                        ldc : writeln('ldc ', code[i].a);
                        ldla : writeln('ldla ', code[i].a);
                        ldl : writeln('ldl ', code[i].a);
                        ldg : writeln('ldg ', code[i].a);
                        stl : writeln('stl ', code[i].a);
                        stg : writeln('stg ', code[i].a);
                        move : writeln('move ', code[i].a);
                        copy : writeln('copy ', code[i].a);
                        addc : writeln('addc ', code[i].a);
                        mulc : writeln('mulc ', code[i].a);
                        jump : writeln('jump ', code[i].a);
                        jumpz: writeln('jumpz ', code[i].a);
                        call : writeln('call ', code[i].a);
                        adjs : writeln('adjs ', code[i].a);
                        sets : writeln('sets ', code[i].a);
                        exit : writeln('exit ', code[i].a)
end end end;

begin { compile }
            word[beginsym ]:= 'begin '; word[endsym ]:= 'end ';
            word[ifsym ]:= 'if '; word[thensym ]:= 'then ';
            word[elsesym ]:= 'else '; word[whilesym ]:= 'while ';
            word[dosym ]:= 'do '; word[casesym ]:= 'case ';
            word[repeatsym]:= 'repeat '; word[untilsym ]:= 'until ';
            word[forsym ]:= 'for '; word[tosym ]:= 'to ';
            word[downtosym]:= 'downto '; word[notsym ]:= 'not ';
            word[divsym ]:= 'div '; word[modsym ]:= 'mod ';
            word[andsym ]:= 'and '; word[orsym ]:= 'or ';
            word[constsym ]:= 'const '; word[varsym ]:= 'var ';
            word[typesym ]:= 'type '; word[arraysym ]:= 'array ';
            word[ofsym ]:= 'of '; word[recordsym]:= 'record ';
            word[progsym ]:= 'program '; word[funcsym ]:= 'function ';
            word[procsym ]:= 'procedure ';
            ttab[intip].size:= 1; ttab[intip].kind:= simple;
            ttab[chartip].size:= 1; ttab[chartip].kind:= simple;
            ttab[booltip].size:= 1; ttab[booltip].kind:= simple;
            tx:= 3; namelist[-1]:= 0; lev:= -1; ix:= 0;
            enter('false ', konst, booltip); itab[ix].val:= ord(false);
            enter('true ', konst, booltip); itab[ix].val:= ord(true);
            enter('maxint ', konst, intip); itab[ix].val:= 32767;
            enter('integer ', tipe, intip);
            enter('char ', tipe, chartip);
            enter('boolean ', tipe, booltip);
            enter('abs ', funkt, intip);
            itab[ix].flevel:= -1; itab[ix].fadr:= fabs; itab[ix].inside:= false;
            enter('sqr ', funkt, intip);
            itab[ix].flevel:= -1; itab[ix].fadr:= fsqr; itab[ix].inside:= false;
            enter('odd ', funkt, booltip);
            itab[ix].flevel:= -1; itab[ix].fadr:= fodd; itab[ix].inside:= false;
            enter('chr ', funkt, chartip);
            itab[ix].flevel:= -1; itab[ix].fadr:= fchr; itab[ix].inside:= false;
            enter('ord ', funkt, intip);
            itab[ix].flevel:= -1; itab[ix].fadr:= ford; itab[ix].inside:= false;
            enter('write ', funkt, 0);
            itab[ix].flevel:= -1; itab[ix].fadr:= fwrite;
            enter('writeln ', funkt, 0);
            itab[ix].flevel:= -1; itab[ix].fadr:= fwriteln;
            enter('read ', funkt, 0);
            itab[ix].flevel:= -1; itab[ix].fadr:= fread;
            enter('readln ', funkt, 0);
            itab[ix].flevel:= -1; itab[ix].fadr:= freadln;
            enter('eoln ', funkt, booltip);
            itab[ix].flevel:= -1; itab[ix].fadr:= feoln; itab[ix].inside:= false;
            namelist[0]:= 0; lev:= 0; cc:= 0; ll:= 0; getch; getsym;
            labeled:= true; cx:= 0; dx:= amax+1;
            skip(progsym); skip(ident); check(lparen);
            repeat getsym; check(ident);
                          if (id<>'input ') and (id<>'output ') then error(129);
            until sym<>comma;
            skip(rparen); skip(semicolon); gen1(jump, 0); block(0); gen0(hhalt);

procedure interpret;
    var pc, sp, j, k, n: integer; i: instr; c: char; h: boolean;
begin pc:= 0; h:= false;
            repeat i:= code[pc]; pc:= pc+1;
                case i.op of
                    add : begin m[sp+1]:= m[sp+1]+m[sp]; sp:= sp+1 end;
                    neg : m[sp]:= -m[sp];
                    mul : begin m[sp+1]:= m[sp+1]*m[sp]; sp:= sp+1 end;
                    divd : begin m[sp+1]:= m[sp+1] div m[sp]; sp:= sp+1 end;
                    remd : begin m[sp+1]:= m[sp+1] mod m[sp]; sp:= sp+1 end;
                    div2 : m[sp]:= m[sp] div 2;
                    rem2 : m[sp]:= m[sp] mod 2;
                    eqli : begin m[sp+1]:= ord(m[sp+1]=m[sp]); sp:= sp+1 end;
                    neqi : begin m[sp+1]:= ord(m[sp+1]<>m[sp]); sp:= sp+1 end;
                    lssi : begin m[sp+1]:= ord(m[sp+1]<m[sp]); sp:= sp+1 end;
                    leqi : begin m[sp+1]:= ord(m[sp+1]<=m[sp]); sp:= sp+1 end;
                    gtri : begin m[sp+1]:= ord(m[sp+1]>m[sp]); sp:= sp+1 end;
                    geqi : begin m[sp+1]:= ord(m[sp+1]>=m[sp]); sp:= sp+1 end;
                    dupl : begin sp:= sp-1; m[sp]:= m[sp+1] end;
                    swap : begin k:= m[sp]; m[sp]:= m[sp+1]; m[sp+1]:= k end;
                    andb : begin if m[sp]=0 then m[sp+1]:= 0; sp:= sp+1 end;
                    orb : begin if m[sp]=1 then m[sp+1]:= 1; sp:= sp+1 end;
                    load : m[sp]:= m[m[sp]];
                    stor : begin m[m[sp]]:= m[sp+1]; sp:= sp+2 end;
                    hhalt: h:= true;
                    wri : begin write(output, m[sp+1]: m[sp]); sp:= sp+2 end;
                    wrc : begin write(output, chr(m[sp])); sp:= sp+1 end;
                    wrl : writeln(output);
                    rdi : begin read(input, m[m[sp]]); sp:= sp+1 end;
                    rdc : begin read(input, c); m[m[sp]]:= ord(c); sp:= sp+1 end;
                    rdl : readln(input);
                    eol : begin sp:= sp-1; m[sp]:= ord(eoln(input)) end;
                    ldc : begin sp:= sp-1; m[sp]:= i.a end;
                    ldla : begin sp:= sp-1; m[sp]:= sp+1+i.a end;
                    ldl : begin sp:= sp-1; m[sp]:= m[sp+1+i.a] end;
                    ldg : begin sp:= sp-1; m[sp]:= m[i.a] end;
                    stl : begin m[sp+i.a]:= m[sp]; sp:= sp+1 end;
                    stg : begin m[i.a]:= m[sp]; sp:= sp+1 end;
                    move : begin k:= m[sp]; j:= m[sp+1]; sp:= sp+2; n:= i.a;
                                              repeat n:= n-1; m[k+n]:= m[j+n] until n=0
                    copy : begin j:= m[sp]; n:= i.a; sp:= sp-n+1;
                                              repeat n:= n-1; m[sp+n]:= m[j+n] until n=0
                    addc : m[sp]:= m[sp]+i.a;
                    mulc : m[sp]:= m[sp]*i.a;
                    jump : pc:= i.a;
                    jumpz: begin if m[sp]=0 then pc:= i.a; sp:= sp+1 end;
                    call : begin sp:= sp-1; m[sp]:= pc; pc:= i.a end;
                    adjs : sp:= sp+i.a;
                    sets : sp:= i.a;
                    exit : begin pc:= m[sp]; sp:= sp+i.a end;
            until h

            assign(infile, 'test.pas');

-- Dr Adrian Johnstone, Senior Lecturer in Computing, Computer Science Dep,
Royal Holloway, University of London, Egham, Surrey, TW20 0EX, England.
Email Tel:+44(0)1784 443425 Fax:+44(0)1784 439786

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