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Давайте создадим компилятор! :: Креншоу Джек
Страница: 132 из 382i := n;
while (i > 0) and not found do
if s = T^[i] then
found := true
else
dec(i);
Lookup := i;
end;
{–}
{ Get an Identifier }
procedure GetName;
begin
while Look = CR do
Fin;
if not IsAlpha(Look) then Expected('Name');
Value := '';
while IsAlNum(Look) do begin
Value := Value + UpCase(Look);
GetChar;
end;
SkipWhite;
end;
{–}
{ Get a Number }
procedure GetNum;
begin
if not IsDigit(Look) then Expected('Integer');
Value := '';
while IsDigit(Look) do begin
Value := Value + Look;
GetChar;
end;
Token := '#';
SkipWhite;
end;
{–}
{ Get an Identifier and Scan it for Keywords }
procedure Scan;
begin
GetName;
Token := KWcode[Lookup(Addr(KWlist), Value, 4) + 1];
end;
{–}
{ Match a Specific Input String }
procedure MatchString(x: string);
begin
if Value <> x then Expected('''' + x + '''');
end;
{–}
{ Generate a Unique Label }
function NewLabel: string;
var S: string;
begin
Str(LCount, S);
NewLabel := 'L' + S;
Inc(LCount);
end;
{–}
{ Post a Label To Output }
procedure PostLabel(L: string);
begin
WriteLn(L, ':');
end;
{–}
{ Output a String with Tab }
procedure Emit(s: string);
begin
Write(TAB, s);
end;
{–}
{ Output a String with Tab and CRLF }
procedure EmitLn(s: string);
begin
Emit(s);
WriteLn;
end;
{–}
{ Parse and Translate an Identifier }
procedure Ident;
begin
GetName;
if Look = '(' then begin
Match('(');
Match(')');
EmitLn('BSR ' + Value);
end
else
EmitLn('MOVE ' + Value + '(PC),D0');
end;
{–}
{ Parse and Translate a Math Factor }
procedure Expression; Forward;
procedure Factor;
begin
if Look = '(' then begin
Match('(');
Expression;
Match(')');
end
else if IsAlpha(Look) then
Ident
else begin
GetNum;
EmitLn('MOVE #' + Value + ',D0');
end;
end;
{–}
{ Parse and Translate the First Math Factor }
procedure SignedFactor;
var s: boolean;
begin
s := Look = '-';
if IsAddop(Look) then begin
GetChar;
SkipWhite;
end;
Factor;
if s then
EmitLn('NEG D0');
end;
{–}
{ Recognize and Translate a Multiply }
procedure Multiply;
begin
Match('*');
Factor;
EmitLn('MULS (SP)+,D0');
end;
{–}
{ Recognize and Translate a Divide }
procedure Divide;
begin
Match('/');
Factor;
EmitLn('MOVE (SP)+,D1');
EmitLn('EXS.L D0');
EmitLn('DIVS D1,D0');
end;
{–}
{ Completion of Term Processing (called by Term and FirstTerm }
procedure Term1;
begin
while IsMulop(Look) do begin
EmitLn('MOVE D0,-(SP)');
case Look of
'*': Multiply;
'/': Divide;
end;
end;
end;
{–}
{ Parse and Translate a Math Term }
procedure Term;
begin
Factor;
Term1;
end;
{–}
{ Parse and Translate a Math Term with Possible Leading Sign }
procedure FirstTerm;
begin
SignedFactor;
Term1;
end;
{–}
{ Recognize and Translate an Add }
procedure Add;
begin
Match('+');
Term;
EmitLn('ADD (SP)+,D0');
end;
{–}
{ Recognize and Translate a Subtract }
procedure Subtract;
begin
Match('-');
Term;
EmitLn('SUB