📄 el.pas
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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,gtr,leq,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 {give value to non-variation} 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 = prosedure 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 else
if sym=readsym then
begin
getsym;
if sym=lparen then
repeat
getsym;
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
else with table[i] do
gen(red,lev-level,adr)
end else error(4);
getsym;
until sym<>comma
else error(40);
if sym<>rparen then error(22);
getsym
end else
if sym=writesym then
begin getsym;
if sym=lparen then
begin
repeat
getsym; expression([rparen,comma]+fsys);
gen(wrt,0,0);
until sym<>comma;
if sym<>rparen then error(22);
getsym
end else error(40)
end;
test(fsys,[ ],19)
end; {statement}
begin{block}
dx:=3; tx0:=tx; table[tx].adr:=cx;
gen(jmp,0,0); {jump from declaration part to statement part}
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(prosedure); 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;
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;
i:instruction;
s:array[1..stacksize] of integer;
function base(l:integer): integer;
var b1:integer;
begin
b1:=b;
while l>0 do
begin b1:=s[b1]; l:=l-1
end;
base:=b1
end;{base}
begin writeln(' START EL ');
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
0:begin t:=b-1;p:=s[t+3];b:=s[t+2];
end;
1:s[t]:=-s[t];
2:begin t:=t-1;s[t]:=s[t]+s[t+1]
end;
3:begin t:=t-1;s[t]:=s[t]-s[t+1]
end;
4:begin t:=t-1;s[t]:=s[t]*s[t+1]
end;
5:begin t:=t-1;s[t]:=s[t] div s[t+1]
end;
6:s[t]:=ord(odd(s[t]));
8:begin t:=t-1;s[t]:=ord(s[t]=s[t+1])
end;
9:begin t:=t-1;s[t]:=ord(s[t]<>s[t+1])
end;
10:begin t:=t-1;s[t]:=ord(s[t]<s[t+1])
end;
11:begin t:=t-1;s[t]:=ord(s[t]>=s[t+1])
end;
12:begin t:=t-1;s[t]:=ord(s[t]>s[t+1])
end;
13:begin t:=t-1;s[t]:=ord(s[t]<=s[t+1])
end;
end;
lod:begin t:=t+1; s[t]:=s[base(1)+a]
end;
sto:begin s[base(1)+a]:=s[t]; t:=t-1
end;
cal:begin
s[t+1]:=base(1);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;
red:begin writeln(' ?? :');
readln(s[base(1)+a]);
end;
wrt:begin writeln(s[t]); t:=t+1
end
end{of with,case}
until p=0;
writeln(' END EL ');
end;{interpret}
begin{main}
writeln('please input source program file name:');
readln(sfile);
assign(fin,sfile);
reset(fin);
for ch:='A' 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 ';
wsym [1]:= beginsym; wsym [2]:= callsym;
wsym [3]:= constsym; wsym [4]:= dosym;
wsym [5]:= endsym; wsym [6]:= ifsym;
wsym [7]:= oddsym; wsym [8]:= procsym;
wsym [9]:= readsym; wsym[10]:= thensym;
wsym[11]:= varsym; wsym[12]:= whilesym;
wsym[13]:= writesym;
ssym ['+']:=plus; ssym['-']:=minus;
ssym ['*']:=times; ssym['/']:=slash;
ssym ['(']:=lparen; ssym[')']:=rparen;
ssym ['=']:=eql; ssym[',']:=comma;
ssym ['.']:=period; ssym['<']:=lss;
ssym ['>']:=gtr; 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 ';
mnemonic[red]:='RED '; mnemonic[wrt]:='WRT ';
declbegsys :=[constsym, varsym, procsym];
statbegsys :=[beginsym, callsym, ifsym, whilesym];
facbegsys :=[ ident, number, lparen];
err:=0;
cc:=0; cx:=0; ll:=0; ch:=' '; kk:=al; getsym;
block(0,0,[period] +declbegsys+statbegsys);
if sym <> period then error(9);
if err=0 then interpret
else write('ERRORS IN EL PROGRAM');
writeln;
close(fin)
end.⌨️ 快捷键说明
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