JК
Давайте создадим компилятор! :: Креншоу Джек
Страница: 253 из 382{–}
{ Recognize a Relop }
function IsRelop(c: char): boolean;
begin
IsRelop := c in ['=', '#', '<', '>'];
end;
{–}
{ Recognize White Space }
function IsWhite(c: char): boolean;
begin
IsWhite := c in [' ', TAB];
end;
{–}
{ Skip Over Leading White Space }
procedure SkipWhite;
begin
while IsWhite(Look) do
GetChar;
end;
{–}
{ Skip Over an End-of-Line }
procedure Fin;
begin
if Look = CR then begin
GetChar;
if Look = LF then
GetChar;
end;
end;
{–}
{ Match a Specific Input Character }
procedure Match(x: char);
begin
if Look = x then GetChar
else Expected('''' + x + '''');
SkipWhite;
end;
{–}
{ Get an Identifier }
function GetName: char;
begin
if not IsAlpha(Look) then Expected('Name');
GetName := UpCase(Look);
GetChar;
SkipWhite;
end;
{–}
{ Get a Number }
function GetNum: char;
begin
if not IsDigit(Look) then Expected('Integer');
GetNum := Look;
GetChar;
SkipWhite;
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;
{–}
{ Post a Label To Output }
procedure PostLabel(L: string);
begin
WriteLn(L, ':');
end;
{–}
{ Load a Variable to the Primary Register }
procedure LoadVar(Name: char);
begin
CheckVar(Name);
EmitLn('MOVE ' + Name + '(PC),D0');
end;
{–}
{ Store the Primary Register }
procedure StoreVar(Name: char);
begin
CheckVar(Name);
EmitLn('LEA ' + Name + '(PC),A0');
EmitLn('MOVE D0,(A0)')
end;
{–}
{ Initialize }
procedure Init;
var i: char;
begin
GetChar;
SkipWhite;
for i := 'A' to 'Z' do
ST[i] := ' ';
end;
{–}
{ Parse and Translate an Expression }
{ Vestigial Version }
procedure Expression;
begin
LoadVar(GetName);
end;
{–}
{ Parse and Translate an Assignment Statement }
procedure Assignment;
var Name: char;
begin
Name := GetName;
Match('=');
Expression;
StoreVar(Name);
end;
{–}
{ Parse and Translate a Block of Statements }
procedure DoBlock;
begin
while not(Look in ['e']) do begin
Assignment;
Fin;
end;
end;
{–}
{ Parse and Translate a Begin-Block }
procedure BeginBlock;
begin
Match('b');
Fin;
DoBlock;
Match('e');
Fin;
end;
{–}
{ Allocate Storage for a Variable }
procedure Alloc(N: char);
begin
if InTable(N) then Duplicate(N);
ST[N] := 'v';
WriteLn(N, ':', TAB, 'DC 0');
end;
{–}
{ Parse and Translate a Data Declaration }
procedure Decl;
var Name: char;
begin
Match('v');
Alloc(GetName);
end;
{–}
{ Parse and Translate Global Declarations }
procedure TopDecls;
begin
while Look <> 'b' do begin
case Look of
'v': Decl;
else Abort('Unrecognized Keyword ' + Look);
end;
Fin;
end;
end;
{–}
{ Main Program }
begin
Init;
TopDecls;
BeginBlock;
end.