PL0程序设计语言
PL0语言可看成是Pascal[1]语言的子集，它的编译程序是一个编译解释执行系统。
PL/0的目标程序为假象栈试计算机的汇编语言，与具体计算机无关。编译原理的课程作业，就是实现一个PL0的编译程序，分两个任务。第一个任务是生成中间代码以及输出运行过程的栈中数据，第二个任务在第一个任务的基础上实现PL0的read和write函数。
program pl0(input, output);
{任务一的代码实现}
label 99;
const norw=11; {保留字个数}
txmax=100; {标识符表长度}
nmax=14; {数字允许的最长位数}
al=10; {标识符表的长度}
amax=2047; {最大地址}
levmax=3; {程序体嵌套的最大深度}
cxmax=200; {代码数组的大小}
type symbol=(nul,ident,number,plus,minus,times,slash,oddsym,
eql,neq,lss,leq,gtr,geq,lparen,rparen,comma,
semicolon,period,becomes,beginsym,endsym,ifsym,
thensym,whilesym,dosym,callsym,
constsym,varsym,procsym);
alfa=packed array[1..al] of char;
objects=(constant,variable,procedur);
{procedure和object在pascal中是关键字，所以分别使用procedur和object替代}
symset=set of symbol;
fct=(lit,opr,lod,sto,cal,int,jmp,jpc);
instruction=packed record
f:fct; {功能码}
l:0..levmax; {层}
a:0..amax; {相对地址}
end;
var fa:text; {文本文件fa用于列出中间程序}
srccode,data:text; {文本文件srccode用于列出源代码、data用于记录运行数据}
ch:char; {最近读到的字符}
sym:symbol; {最近读到的符号}
id:alfa; {最近读到的标识符}
num:integer; {最近读到的数}
cc:integer; {字符计数}
ll:integer; {行长}
kk:integer;
cx:integer; {代码分配下标}
line:array[1..81] of char;
a:alfa;
code:array[0..cxmax] of instruction;
word:array[1..norw] of alfa;
wsym:array[1..norw] of symbol;
ssym:array[char] of symbol;
mnemonic:array[fct] of packed array[1..5] of char;
declbegsys, statbegsys, facbegsys:symset;
table:array[0..txmax] of record
name:alfa;
case kind:objects of
constant:(val:integer);
variable,procedur:(level,adr,size:integer)
end;
fin,fout:text;
fname:string;
err:integer;
endf:boolean;
procedure error(n:integer);
begin
writeln('****',' ':cc-1,'!',n:2);
writeln(srccode,'****','':cc-1,'!',n:2);
err:=err+1;
end; {error}
procedure exitp;
begin
endf:=true;
close(fin);
writeln;
exit;
end;
procedure getsym;
var i,j,k:integer;
procedure getch;
begin
if cc=ll then begin
if eof(fin) then begin
write('program incomplete');
close(fin);
writeln;
exitp;
(* goto 99;*)
end;
ll:=0;
cc:=0;
write(cx:5,' ');
write(srccode,cx:5,' ');
while not eoln(fin) do begin
ll:=ll+1;
read(fin,ch);
write(ch);
write(srccode,ch);
line[ll]:=ch;
end;
writeln;
ll:=ll+1;
line[ll]:=' ';
readln(fin);
writeln(srccode);
end;
cc:=cc+1;
ch:=line[cc];
end; {getch}
begin {getsym}
while ch=' ' do getch;
if ch in ['a'..'z'] then begin
k:=0;
repeat
if k=kk then kk:=k
else repeat
a[kk]:=' ';
kk:=kk-1;
until kk=k;
id:=a;
i:=1;
j:=norw;
repeat
k:=(i+j) div 2;
if id<=word[k] then j:=k-1;
if id>=word[k] then i:=k+1;
until i>j;
if i-1>j then sym:=wsym[k] else sym:=ident;
end else if ch in ['0'..'9'] then begin
k:=0;
num:=0;
sym:=number;
repeat
num:=10*num+(ord(ch)-ord('0'));
k:=k+1;
getch;
until not(ch in['0'..'9']);
if k>nmax then error(30);
end else if ch=':' then begin
getch;
if ch='=' then begin
sym:=becomes;
getch;
end else sym:=nul;
end else if ch='<' then begin
getch;
if ch='=' then begin
sym:=leq;
getch;
end else sym:=lss;
end else if ch='>' then begin
getch;
if ch='=' then begin
sym:=geq;
getch;
end else sym:=gtr;
end else begin
sym:=ssym[ch];
getch;
end;
end; {getsym}
procedure gen(x:fct;y,z:integer);
begin
if cx>cxmax then begin
write('program too long');
(* goto 99;*)
end;
with code[cx] do begin
f:=x;
l:=y;
a:=z;
end;
cx:=cx+1;
end; {gen}
procedure test(s1,s2:symset;n:integer);
begin
if not(sym in s1) then begin
error(n);
s1:=s1+s2;
while not(sym in s1) do getsym;
end;
end; {test}
procedure block(lev,tx:integer;fsys:symset);
var dx:integer; {数据分配下标}
tx0:integer; {起始标识符表的下标}
cx0:integer; {起始代码的下标}
procedure enter(k:objects);
begin {把objects填入标识符表中}
tx:=tx+1;
with table[tx] do begin
name:=id;
kind:=k;
case k of
constant: begin
if num>amax then begin error(30); num:=0; end;
val:=num;
end;
variable: begin
level:=lev;
adr:=dx;
dx:=dx+1;
end;
procedur: level:=lev;
end;
end;
end; {enter}
function position(id:alfa):integer;
var i:integer;
begin {在标识符表中查标识符id}
table[0].name:=id;
i:=tx;
while table[i].name<>id do i:=i-1;
position:=i;
end; {position}
procedure constdeclaration;
begin
if sym=ident then begin
getsym;
if sym in [eql,becomes] then begin
if sym=becomes then error(1);
getsym;
if sym=number then begin
enter(constant);
getsym;
end else error(2);
end else error(3);
end else error(4);
end; {constdeclaration}
procedure vardeclaration;
begin
if sym=ident then begin
enter(variable);
getsym;
end else error(4);
end; {vardeclaration}
procedure listcode;
var i:integer;
begin
for i:=cx0 to cx-1 do
with code[i] do begin
writeln(i,mnemonic[f]:5,l:3,a:5);
writeln(fa,i:4,mnemonic[f]:5,l:3,a:5);
end;
end; {listcode}
procedure statement(fsys:symset);
var i,cx1,cx2:integer;
procedure expression(fsys:symset);
var addop:symbol;
procedure term(fsys:symset);
var mulop:symbol;
procedure factor(fsys:symset);
var i:integer;
begin
test(facbegsys,fsys,24);
while sym in facbegsys do begin
if sym=ident then begin
i:=position(id);
if i=0 then error(11)
else with table[i] do
case kind of
constant:gen(lit,0,val);
variable:gen(lod,lev-level,adr);
procedur:error(21);
end;
getsym;
end else if sym=number then begin
if num>amax then begin
error(30);
num:=0;
end;
gen(lit,0,num);
getsym;
end else if sym=lparen then begin
getsym;
expression([rparen]+fsys);
if sym=rparen then getsym
else error(22);
end;
test(fsys,facbegsys,23);
end;
end; {factor}
begin {term}
factor([times,slash]+fsys);
while sym in [times,slash] do begin
mulop:=sym;
getsym;
factor(fsys+[times,slash]);
if mulop=times then gen(opr,0,4) else gen(opr,0,5)
end;
end; {term}
begin {expression}
if sym in [plus,minus] then begin
addop:=sym;
getsym;
term(fsys+[plus,minus]);
if addop=minus then gen(opr,0,1);
end else term(fsys+[plus,minus]);
while sym in [plus,minus] do begin
addop:=sym;
getsym;
term(fsys+[plus,minus]);
if addop=plus then gen(opr,0,2) else gen(opr,0,3);
end;
end; {expression}
procedure condition(fsys:symset);
var relop:symbol;
begin
if sym=oddsym then begin
getsym;
expression(fsys);
gen(opr,0,6);
end else begin
expression([eql,neq,lss,leq,gtr,geq]+fsys);
if not(sym in [eql,neq,lss,leq,gtr,geq]) then error(20)
else begin
relop:=sym;
getsym;
expression(fsys);
case relop of
eql:gen(opr,0,8);
neq:gen(opr,0,9);
lss:gen(opr,0,10);
geq:gen(opr,0,11);
gtr:gen(opr,0,12);
leq:gen(opr,0,13);
end;
end;
end;
end; {condition}
begin {statement}
if sym=ident then begin
i:=position(id);
if i=0 then error(11)
else if table[i].kind<>variable then begin
error(12);
i:=0;
end;
getsym;
if sym=becomes then getsym else error(13);
expression(fsys);
if i<>0 then with table[i] do gen(sto,lev-level,adr);
end else if sym=callsym then begin
getsym;
if sym<>ident then error(14)
else begin
i:=position(id);
if i=0 then error(11) else with table[i] do
if kind=procedur then gen(cal,lev-level,adr)
else error(15);
getsym;
end;
end else if sym=ifsym then begin
getsym;
condition([thensym,dosym]+fsys);
if sym=thensym then getsym
else error(16);
cx1:=cx;
gen(jpc,0,0);
statement(fsys);
code[cx1].a:=cx;
end else if sym=beginsym then begin
getsym;
statement([semicolon,endsym]+fsys);
while sym in [semicolon]+statbegsys do begin
if sym=semicolon then getsym
else error(10);
statement([semicolon,endsym]+fsys);
end;
if sym=endsym then getsym else error(17);
end else if sym=whilesym then begin
cx1:=cx;
getsym;
condition([dosym]+fsys);
cx2:=cx;
gen(jpc,0,0);
if sym=dosym then getsym else error(18);
statement(fsys);
gen(jmp,0,cx1);
code[cx2].a:=cx;
end;
test(fsys,[],19);
end; {statement}
begin {block}
dx:=3;
tx0:=tx;
table[tx].adr:=cx;
gen(jmp,0,0);
if lev>levmax then error(32);
repeat
if sym=constsym then begin
getsym;
repeat
constdeclaration;
while sym=comma do begin
getsym;
constdeclaration;
end;
if sym=semicolon then getsym else error(5);
until sym<>ident;
end;
if sym=varsym then begin
getsym;
repeat;
vardeclaration;
while sym=comma do begin
getsym;
vardeclaration;
end;
if sym=semicolon then getsym else error(5);
until sym<>ident;
end;
while sym=procsym do begin
getsym;
if sym=ident then begin
enter(procedur);
getsym;
end else error(4);
if sym=semicolon then getsym else error(5);
block(lev+1,tx,[semicolon]+fsys);
if sym=semicolon then begin
getsym;
test(statbegsys+[ident,procsym],fsys,6);
end else error(5);
end;
test(statbegsys+[ident],declbegsys,7);
until not(sym in declbegsys);
code[table[tx0].adr].a:=cx;
with table[tx0] do begin
adr:=cx;
size:= dx;
end;
cx0:=cx;
gen(int,0,dx);
statement([semicolon,endsym]+fsys);
gen(opr,0,0);
test(fsys,[],8);
listcode;
end; {block}
procedure interpret;
const stacksize=500;
var p,b,t:integer; {程序地址寄存器，基地址寄存器，栈顶地址寄存器}
i:instruction; {指令寄存器}
s:array[1..stacksize] of integer; {数据存贮}
function base(l:integer):integer;
var bl:integer;
begin
bl:=b; {顺静态链求层差为l的层的基地址}
while l>0 do begin
bl:=s[bl];
l:=l-1;
end;
base:=bl;
end; {base}
begin
writeln('start pl/0');
writeln(data,'start pl/0');
t:=0; b:=1; p:=0;
s[1]:=0; s[2]:=0; s[3]:=0;
repeat
i:=code[p];
p:=p+1;
with i do case f of
lit: begin t:=t+1; s[t]:=a; end;
opr: case a of {operator}
0: begin {return}
t:=b-1;
p:=s[t+3];
b:=s[t+2];
end;
1: s[t]:=-s[t];
2: begin t:=t-1; s[t]:=s[t]+s[t+1]; end;
3: begin t:=t-1; s[t]:=s[t]-s[t+1]; end;
4: begin t:=t-1; s[t]:=s[t]*s[t+1]; end;
5: begin t:=t-1; s[t]:=s[t] div s[t+1]; end;
6: s[t]:=ord(odd(s[t]));
8: begin t:=t-1; s[t]:=ord(s[t]=s[t+1]); end;
9: begin t:=t-1; s[t]:=ord(s[t]<>s[t+1]); end;
10:begin t:=t-1; s[t]:=ord(s[t]=s[t+1]); end;
12:begin t:=t-1; s[t]:=ord(s[t]>s[t+1]); end;
13:begin t:=t-1; s[t]:=ord(s[t]<=s[t+1]); end;
end;
lod: begin t:=t+1; s[t]:=s[base(l)+a]; end;
sto: begin s[base(l)+a]:=s[t]; writeln(s[t]); writeln(data,s[t]);t:=t-1; end;
cal: begin s[t+1]:=base(l); s[t+2]:=b;
s[t+3]:=p; b:=t+1; p:=a; end;
int: t:=t+a;
jmp: p:=a;
jpc: begin if s[t]=0 then p:=a; t:=t-1; end;
end; {with, case}
until p=0;
writeln('end pl/0');
writeln(data,'endpl/0');
close(data);
end; {interpret}
begin {main}
for ch:=' ' to '!' do ssym[ch]:=nul;
word[1]:='begin '; word[2]:='call ';
word[3]:='const '; word[4]:='do ';
word[5]:='end '; word[6]:='if ';
word[7]:='odd '; word[8]:='procedure ';
word[9]:='then '; word[10]:='var ';
word[11]:='while ';
wsym[1]:=beginsym; wsym[2]:=callsym;
wsym[3]:=constsym; wsym[4]:=dosym;
wsym[5]:=endsym; wsym[6]:=ifsym;
wsym[7]:=oddsym; wsym[8]:=procsym;
wsym[9]:=thensym; wsym[10]:=varsym;
wsym[11]:=whilesym;
ssym['+']:=plus; ssym['-']:=minus;
ssym['*']:=times; ssym['/']:=slash;
ssym['(']:=lparen; ssym[')']:=rparen;
ssym['=']:=eql; ssym[',']:=comma;
ssym['.']:=period; ssym['#']:=neq;
ssym[';']:=semicolon;
mnemonic[lit]:='lit '; mnemonic[opr]:='opr ';
mnemonic[lod]:='lod '; mnemonic[sto]:='sto ';
mnemonic[cal]:='cal '; mnemonic[int]:='int ';
mnemonic[jmp]:='jmp '; mnemonic[jpc]:='jpc ';
declbegsys:=[constsym,varsym,procsym];
statbegsys:=[beginsym,callsym,ifsym,whilesym];
facbegsys:=[ident,number,lparen];
(* page(output);*)
endf:=false;
assign(srccode,'SRCCODE.txt');
rewrite(srccode);
assign(data,'STACK.txt');
rewrite(data);
write('Enter the path of the file:');
write(srccode,'Enter the path of the file:');
readln(fname);
writeln(srccode,fname);
assign(fin,fname); reset(fin);
err:=0;
cc:=0; cx:=0; ll:=0;
ch:=' '; kk:=al;
getsym;
assign(fa,'MIDCODE.txt');
rewrite(fa);
block(0,0,[period]+declbegsys+statbegsys);
close(fa);
close(srccode);
if sym<>period then error(9);
if err=0 then interpret else write('ERRORS IN PL/0 PROGRAM');
99: {这个标号原来是用于退出程序的，由于Turbo Pascal不支持跨过程的跳转，所以使用exip函数替代}
close(fin);
writeln;
end. program pl0(input, output);
{任务二的代码实现}
label 99;
const norw=13; {保留字个数}
txmax=100; {标识符表长度}
nmax=14; {数字允许的最长位数}
al=10; {标识符表的长度}
amax=2047; {最大地址}
levmax=3; {程序体嵌套的最大深度}
cxmax=200; {代码数组的大小}
type symbol=(nul,ident,number,plus,minus,times,slash,oddsym,
eql,neq,lss,leq,gtr,geq,lparen,rparen,comma,
semicolon,period,becomes,beginsym,endsym,ifsym,
thensym,whilesym,writesym,readsym,dosym,callsym,
constsym,varsym,procsym);
alfa=packed array[1..al] of char;
objects=(constant,variable,procedur);
{procedure和object在pascal中是关键字，所以分别使用procedur和object替代}
symset=set of symbol;
fct=(lit,opr,lod,sto,cal,int,jmp,jpc);
instruction=packed record
f:fct;{功能码}
l:0..levmax; {层}
a:0..amax; {相对地址}
end;
var fa:text;{文本文件fa用于列出中间代码}
srccode,iofile:text;
ch:char; {最近读到的字符}
sym:symbol; {最近读到的符号}
id:alfa; {最近读到的标识符}
num:integer; {最近读到的数}
cc:integer; {字符计数}
ll:integer; {行长}
kk:integer;
cx:integer; {代码分配下标}
line:array[1..81] of char;
a:alfa;
code:array[0..cxmax] of instruction;
word:array[1..norw] of alfa;
wsym:array[1..norw] of symbol;
ssym:array[char] of symbol;
mnemonic:array[fct] of packed array[1..5] of char;
declbegsys, statbegsys, facbegsys:symset;
table:array[0..txmax] of record
name:alfa;
case kind:objects of
constant:(val:integer);
variable,procedur:(level,adr,size:integer)
end;
fin,fout:text;
fname:string;
err:integer;
endf:boolean;
procedure error(n:integer);
begin
writeln('****','':cc-1,'!',n:2);
writeln(srccode,'****','':cc-1,'!',n:2);
err:=err+1;
end; {error}
procedure exitp;
begin
endf:=true;
close(fin);
writeln;
exit;
end;
procedure getsym;
var i,j,k:integer;
procedure getch;
begin
if cc=ll then begin
if eof(fin) then begin
write('program incomplete');
close(fin);
writeln;
exitp;
(*goto 99;*)
end;
ll:=0;
cc:=0;
write(cx:5,' ');
write(srccode,cx:5,' ');
while not eoln(fin) do begin
ll:=ll+1;
read(fin,ch);
write(ch);
write(srccode,ch);
line[ll]:=ch;
end;
writeln;
ll:=ll+1;
line[ll]:=' ';
readln(fin);
writeln(srccode);
end;
cc:=cc+1;
ch:=line[cc];
end; {getch}
begin {getsym}
while ch=' ' do getch;
if ch in ['a'..'z'] then begin
k:=0;
repeat
if k=kk then kk:=k
else repeat
a[kk]:=' ';
kk:=kk-1;
until kk=k;
id:=a;
i:=1;
j:=norw;
repeat
k:=(i+j) div 2;
if id<=word[k] then j:=k-1;
if id>=word[k] then i:=k+1;
until i>j;
if i-1>j then sym:=wsym[k] else sym:=ident;
end else if ch in ['0'..'9'] then begin
k:=0;
num:=0;
sym:=number;
repeat
num:=10*num+(ord(ch)-ord('0'));
k:=k+1;
getch;
until not(ch in['0'..'9']);
if k>nmax then error(30);
end else if ch=':' then begin
getch;
if ch='=' then begin
sym:=becomes;
getch;
end else sym:=nul;
end else if ch='<' then begin
getch;
if ch='=' then begin
sym:=leq;
getch;
end else sym:=lss;
end else if ch='>' then begin
getch;
if ch='=' then begin
sym:=geq;
getch;
end else sym:=gtr;
end else begin
sym:=ssym[ch];
getch;
end;
end; {getsym}
procedure gen(x:fct;y,z:integer);
begin
if cx>cxmax then begin
write('program too long');
(*goto 99;*)
end;
with code[cx] do begin
f:=x;
l:=y;
a:=z;
end;
cx:=cx+1;
end; {gen}
procedure test(s1,s2:symset;n:integer);
begin
if not(sym in s1) then begin
error(n);
s1:=s1+s2;
while not(sym in s1) do getsym;
end;
end; {test}
procedure block(lev,tx:integer;fsys:symset);
var dx:integer; {数据分配下标}
tx0:integer; {起始标识符表的下标}
cx0:integer; {起始代码的下标}
procedure enter(k:objects);
begin {把objects填入标识符表中}
tx:=tx+1;
with table[tx] do begin
name:=id;
kind:=k;
case k of
constant: begin
if num>amax then begin error(30); num:=0; end;
val:=num;
end;
variable: begin
level:=lev;
adr:=dx;
dx:=dx+1;
end;
procedur: level:=lev;
end;
end;
end; {enter}
function position(id:alfa):integer;
var i:integer;
begin {在标识符表中查标识符id}
table[0].name:=id;
i:=tx;
while table[i].name<>id do i:=i-1;
position:=i;
end; {position}
procedure constdeclaration;
begin
if sym=ident then begin
getsym;
if sym in [eql,becomes] then begin
if sym=becomes then error(1);
getsym;
if sym=number then begin
enter(constant);
getsym;
end else error(2);
end else error(3);
end else error(4);
end; {constdeclaration}
procedure vardeclaration;
begin
if sym=ident then begin
enter(variable);
getsym;
end else error(4);
end; {vardeclaration}
procedure listcode;
var i:integer;
begin
for i:=cx0 to cx-1 do
with code[i] do begin
writeln(i,mnemonic[f]:5,l:3,a:5);
writeln(fa,i:4,mnemonic[f]:5,l:3,a:5);
end;
end; {listcode}
procedure statement(fsys:symset);
var i,cx1,cx2:integer;
procedure expression(fsys:symset);
var addop:symbol;
procedure term(fsys:symset);
var mulop:symbol;
procedure factor(fsys:symset);
var i:integer;
begin
test(facbegsys,fsys,24);
while sym in facbegsys do begin
if sym=ident then begin
i:=position(id);
if i=0 then error(11)
else with table[i] do
case kind of
constant:gen(lit,0,val);
variable:gen(lod,lev-level,adr);
procedur:error(21);
end;
getsym;
end else if sym=number then begin
if num>amax then begin
error(31);
num:=0;
end;
gen(lit,0,num);
getsym;
end else if sym=lparen then begin
getsym;
expression([rparen]+fsys);
if sym=rparen then getsym
else error(22);
end;
test(fsys,facbegsys,23);
end;
end; {factor}
begin {term}
factor([times,slash]+fsys);
while sym in [times,slash] do begin
mulop:=sym;
getsym;
factor(fsys+[times,slash]);
if mulop=times then gen(opr,0,4) else gen(opr,0,5)
end;
end; {term}
begin {expression}
if sym in [plus,minus] then begin
addop:=sym;
getsym;
term(fsys+[plus,minus]);
if addop=minus then gen(opr,0,1);
end else term(fsys+[plus,minus]);
while sym in [plus,minus] do begin
addop:=sym;
getsym;
term(fsys+[plus,minus]);
if addop=plus then gen(opr,0,2) else gen(opr,0,3);
end;
end; {expression}
procedure condition(fsys:symset);
var relop:symbol;
begin
if sym=oddsym then begin
getsym;
expression(fsys);
gen(opr,0,6);
end else begin
expression([eql,neq,lss,leq,gtr,geq]+fsys);
if not(sym in [eql,neq,lss,leq,gtr,geq]) then error(20)
else begin
relop:=sym;
getsym;
expression(fsys);
case relop of
eql:gen(opr,0,8);
neq:gen(opr,0,9);
lss:gen(opr,0,10);
geq:gen(opr,0,11);
gtr:gen(opr,0,12);
leq:gen(opr,0,13);
end;
end;
end;
end; {condition}
begin {statement}
if sym=ident then begin
i:=position(id);
if i=0 then error(11)
else if table[i].kind<>variable then begin
error(12);
i:=0;
end;
getsym;
if sym=becomes then getsym else error(13);
expression(fsys);
if i<>0 then with table[i] do gen(sto,lev-level,adr);
end else if sym=readsym then begin {添加read语句执行功能}
getsym;
if sym<>lparen then error(34)
else repeat
getsym;
if sym=ident then i:=position(id)
else i:=0;
if i=0 then error(35)
else with table[i] do begin
gen(opr,0,16);
gen(sto,lev-level,adr);
end;
getsym;
until sym<>comma;
if sym<>rparen then begin
error(33);
while not(sym in fsys) do getsym;
end else getsym;
end else if sym=writesym then begin {添加write语句执行功能}
getsym;
if sym=lparen then begin
repeat
getsym;
expression([rparen,comma]+fsys);
gen(opr,0,14);
until sym<>comma;
if sym<>rparen then error(33) else getsym;
end;
gen(opr,0,15);
end else if sym=callsym then begin
getsym;
if sym<>ident then error(14)
else begin
i:=position(id);
if i=0 then error(11) else with table[i] do
if kind=procedur then gen(cal,lev-level,adr)
else error(15);
getsym;
end;
end else if sym=ifsym then begin
getsym;
condition([thensym,dosym]+fsys);
if sym=thensym then getsym
else error(16);
cx1:=cx;
gen(jpc,0,0);
statement(fsys);
code[cx1].a:=cx;
end else if sym=beginsym then begin
getsym;
statement([semicolon,endsym]+fsys);
while sym in [semicolon]+statbegsys do begin
if sym=semicolon then getsym
else error(10);
statement([semicolon,endsym]+fsys);
end;
if sym=endsym then getsym else error(17);
end else if sym=whilesym then begin
cx1:=cx;
getsym;
condition([dosym]+fsys);
cx2:=cx;
gen(jpc,0,0);
if sym=dosym then getsym else error(18);
statement(fsys);
gen(jmp,0,cx1);
code[cx2].a:=cx;
end;
test(fsys,[],19);
end; {statement}
begin {block}
dx:=3;
tx0:=tx;
table[tx].adr:=cx;
gen(jmp,0,0);
if lev>levmax then error(32);
repeat
if sym=constsym then begin
getsym;
repeat
constdeclaration;
while sym=comma do begin
getsym;
constdeclaration;
end;
if sym=semicolon then getsym else error(5);
until sym<>ident;
end;
if sym=varsym then begin
getsym;
repeat;
vardeclaration;
while sym=comma do begin
getsym;
vardeclaration;
end;
if sym=semicolon then getsym else error(5);
until sym<>ident;
end;
while sym=procsym do begin
getsym;
if sym=ident then begin
enter(procedur);
getsym;
end else error(4);
if sym=semicolon then getsym else error(5);
block(lev+1,tx,[semicolon]+fsys);
if sym=semicolon then begin
getsym;
test(statbegsys+[ident,procsym],fsys,6);
end else error(5);
end;
test(statbegsys+[ident],declbegsys,7);
until not(sym in declbegsys);
code[table[tx0].adr].a:=cx;
with table[tx0] do begin
adr:=cx;
size:=dx;
end;
cx0:=cx;
gen(int,0,dx);
statement([semicolon,endsym]+fsys);
gen(opr,0,0);
test(fsys,[],8);
listcode;
end; {block}
procedure interpret;
const stacksize=500;
var p,b,t:integer; {程序地址寄存器，基地址寄存器，栈顶地址寄存器}
i:instruction; {指令寄存器}
s:array[1..stacksize] of integer; {数据存贮}
function base(l:integer):integer;
var bl:integer;
begin
bl:=b; {顺静态链求层差为l的层的基地址}
while l>0 do begin
bl:=s[bl];
l:=l-1;
end;
base:=bl;
end; {base}
begin
(* writeln('start pl0');*)
t:=0; b:=1; p:=0;
s[1]:=0; s[2]:=0; s[3]:=0;
repeat
i:=code[p];
p:=p+1;
with i do case f of
lit: begin t:=t+1; s[t]:=a; end;
opr: case a of {operator}
0: begin {return}
t:=b-1;
p:=s[t+3];
b:=s[t+2];
end;
1: s[t]:=-s[t];
2: begin t:=t-1; s[t]:=s[t]+s[t+1]; end;
3: begin t:=t-1; s[t]:=s[t]-s[t+1]; end;
4: begin t:=t-1; s[t]:=s[t]*s[t+1]; end;
5: begin t:=t-1; s[t]:=s[t] div s[t+1]; end;
6: s[t]:=ord(odd(s[t]));
8: begin t:=t-1; s[t]:=ord(s[t]=s[t+1]); end;
9: begin t:=t-1; s[t]:=ord(s[t]<>s[t+1]); end;
10:begin t:=t-1; s[t]:=ord(s[t]=s[t+1]); end;
12:begin t:=t-1; s[t]:=ord(s[t]>s[t+1]); end;
13:begin t:=t-1; s[t]:=ord(s[t]<=s[t+1]); end;
14:begin write(s[t]); write(iofile,s[t]); t:=t-1; end;
15:begin writeln; writeln(iofile); end; {输出换行操作}
16:begin t:=t+1; write(':'); write(iofile,':'); readln(s[t]);
writeln(iofile,s[t]); end; {是接受键盘值输入}
end;
lod: begin t:=t+1; s[t]:=s[base(l)+a]; end;
sto: begin s[base(l)+a]:=s[t]; (* writeln(s[t]) *) t:=t-1; end;
cal: begin s[t+1]:=base(l); s[t+2]:=b;
s[t+3]:=p; b:=t+1; p:=a; end;
int: t:=t+a;
jmp: p:=a;
jpc: begin if s[t]=0 then p:=a; t:=t-1; end;
end; {with, case}
until p=0;
close(iofile);
end; {interpret}
begin {main}
for ch:=' ' to '!' do ssym[ch]:=nul;
word[1]:='begin '; word[2]:='call ';
word[3]:='const '; word[4]:='do ';
word[5]:='end '; word[6]:='if ';
word[7]:='odd '; word[8]:='procedure ';
word[9]:='read '; word[10]:='then ';
word[11]:='var '; word[12]:='while ';
word[13]:='write '; {添加了保留字write和read}
wsym[1]:=beginsym; wsym[2]:=callsym;
wsym[3]:=constsym; wsym[4]:=dosym;
wsym[5]:=endsym; wsym[6]:=ifsym;
wsym[7]:=oddsym; wsym[8]:=procsym;
wsym[9]:=readsym; wsym[10]:=thensym;
wsym[11]:=varsym; wsym[12]:=whilesym;
wsym[13]:=writesym; {添加符号列表}
ssym['+']:=plus; ssym['-']:=minus;
ssym['*']:=times; ssym['/']:=slash;
ssym['(']:=lparen; ssym[')']:=rparen;
ssym['=']:=eql; ssym[',']:=comma;
ssym['.']:=period; ssym['#']:=neq;
ssym[';']:=semicolon; {初始化符号列表}
mnemonic[lit]:='lit '; mnemonic[opr]:='opr ';
mnemonic[lod]:='lod '; mnemonic[sto]:='sto ';
mnemonic[cal]:='cal '; mnemonic[int]:='int ';
mnemonic[jmp]:='jmp '; mnemonic[jpc]:='jpc ';
declbegsys:=[constsym,varsym,procsym];
statbegsys:=[beginsym,callsym,ifsym,whilesym];
facbegsys:=[ident,number,lparen];
(* page(output) *)
endf:=false;
assign(srccode,'SRCCODE.txt');
rewrite(srccode);
write('Enter the path of the file:');
write(srccode,'Enter the path of the file:');
readln(fname);
writeln(srccode,fname);
assign(fin,fname); reset(fin);
err:=0;
cc:=0; cx:=0; ll:=0;
ch:=' '; kk:=al;
getsym;
assign(fa,'MIDCODE.txt');
assign(iofile,'IO.txt');
rewrite(fa);
rewrite(iofile);
block(0,0,[period]+declbegsys+statbegsys);
close(fa);
close(srccode);
if sym<>period then error(9);
if err=0 then interpret else write('ERRORS IN PL/0 PROGRAM');
99: {这个标号原来是用于退出程序的，由于Turbo Pascal不支持跨过程的跳转，所以使用exip函数替代}
close(fin);
writeln;
end.