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program calc1;
{$H+}
uses
typinfo, sysutils, character;
type
TokenType = (TT_Integer, TT_Plus, TT_Minus, TT_Asterisk, TT_Slash, TT_Eof,
TT_LParen, TT_RParen);
Token = class
TokenType: TokenType;
constructor Create(Type_: TokenType);
function ToStr: String; virtual;
end;
TokenInteger = class(Token)
Val: Integer;
constructor Create(Value_: Integer);
function ToStr: String; override;
end;
TokenPlus = class(Token)
constructor Create;
end;
TokenMinus = class(Token)
constructor Create;
end;
TokenEof = class(Token)
constructor Create;
end;
TLexer = class
Text: AnsiString;
CurPos: Integer;
constructor Create(Text_: AnsiString);
procedure Error;
procedure SkipWhitespace;
function AtEnd: Boolean;
function CurChar: Char;
function GetInteger: Integer;
function GetNextToken: Token;
end;
TInterpreter = class
Lexer: TLexer;
CurrentToken: Token;
constructor Create(Lexer_: TLexer);
procedure Error;
procedure Eat(T: TokenType);
function Factor: Integer;
function Expr: Integer;
function Term: Integer;
end;
constructor Token.Create(Type_: TokenType);
begin
inherited Create;
TokenType := Type_;
end;
function Token.ToStr: String;
begin
Result := GetEnumName(TypeInfo(TokenType), Ord(Self.TokenType));
end;
constructor TokenInteger.Create(Value_: Integer);
begin
inherited Create(TT_Integer);
Val := Value_;
end;
function TokenInteger.ToStr: String;
begin
Result := inherited;
Result := Result + '(' + IntToStr(Val) + ')';
end;
constructor TokenPlus.Create;
begin
inherited Create(TT_Plus);
end;
constructor TokenMinus.Create;
begin
inherited Create(TT_Minus);
end;
constructor TokenEof.Create;
begin
inherited Create(TT_Eof);
end;
constructor TLexer.Create(Text_: String);
begin
inherited Create;
Text := Text_;
CurPos := 1;
end;
procedure TLexer.Error;
begin
Raise Exception.Create('invalid input');
end;
procedure TLexer.SkipWhitespace;
begin
while (not AtEnd) and IsWhiteSpace(CurChar) do
Inc(CurPos);
end;
function TLexer.AtEnd: Boolean;
begin
Result := CurPos > Length(Text);
end;
function TLexer.CurChar: Char;
begin
Result := Text[CurPos];
end;
function TLexer.GetInteger: Integer;
var
Start: Integer;
begin
Start := CurPos;
while (not AtEnd) and IsDigit(CurChar) do
Inc(CurPos);
Result := StrToInt(Copy(Text, Start, CurPos - Start));
end;
function TLexer.GetNextToken: Token;
begin
SkipWhitespace;
if AtEnd then
begin
Result := TokenEof.Create;
Exit;
end;
if IsDigit(CurChar) then
begin
Result := TokenInteger.Create(GetInteger);
end
else if CurChar = '+' then
begin
Result := TokenPlus.Create;
Inc(CurPos);
end
else if CurChar = '-' then
begin
Result := TokenMinus.Create;
Inc(CurPos);
end
else if CurChar = '*' then
begin
Result := Token.Create(TT_Asterisk);
Inc(CurPos);
end
else if CurChar = '/' then
begin
Result := Token.Create(TT_Slash);
Inc(CurPos);
end
else if CurChar = '(' then
begin
Result := Token.Create(TT_LParen);
Inc(CurPos);
end
else if CurChar = ')' then
begin
Result := Token.Create(TT_RParen);
Inc(CurPos);
end
else
Error;
end;
constructor TInterpreter.Create(Lexer_: TLexer);
begin
Lexer := Lexer_;
CurrentToken := Lexer.GetNextToken;
end;
procedure TInterpreter.Error;
begin
Raise Exception.Create('syntax error');
end;
procedure TInterpreter.Eat(T: TokenType);
begin
if CurrentToken.TokenType = T then
begin
CurrentToken := Lexer.GetNextToken;
end
else
Error;
end;
function TInterpreter.Factor: Integer;
var
T: Token;
begin
T := CurrentToken;
if T.TokenType = TT_Integer then
begin
Eat(TT_Integer);
Result := TokenInteger(T).Val;
end
else if T.TokenType = TT_LParen then
begin
Eat(TT_LParen);
Result := Expr;
Eat(TT_RParen);
end
else
Error;
end;
function TInterpreter.Expr: Integer;
var
Tok: Token;
begin
// expr : term ((PLUS|MINUS) term)*
// term : factor ((MUL|DIV) factor)*
// factor : INTEGER | LPAREN expr RPAREN
Result := Term;
while CurrentToken.TokenType in [TT_Plus, TT_Minus] do
begin
Tok := CurrentToken;
if Tok.TokenType = TT_Plus then
begin
Eat(TT_Plus);
Result := Round(Result + Term);
end
else if Tok.TokenType = TT_Minus then
begin
Eat(TT_Minus);
Result := Round(Result - Term);
end;
end;
end;
function TInterpreter.Term: Integer;
var
Tok: Token;
begin
Result := Factor;
while CurrentToken.TokenType in [TT_Asterisk, TT_Slash] do
begin
Tok := CurrentToken;
if Tok.TokenType = TT_Asterisk then
begin
Eat(TT_Asterisk);
Result := Result * Factor;
end
else if Tok.TokenType = TT_Slash then
begin
Eat(TT_Slash);
Result := Round(Result / Factor);
end;
end;
end;
var
Lexer: TLexer;
Interp: TInterpreter;
Line: String;
I: Integer;
procedure InterpString(S: String);
begin
Lexer := TLexer.Create(S);
Interp := TInterpreter.Create(Lexer);
WriteLn(Interp.Expr);
FreeAndNil(Interp);
end;
procedure InputLoop;
begin
while True do
begin
Write('calc> ');
if Eof(Input) then break;
ReadLn(Line);
if Length(Line) = 0 then continue;
InterpString(Line);
end;
end;
begin
if ParamCount > 0 then
begin
Line := '';
for I := 1 to ParamCount do
begin
Line := Line + ParamStr(I);
end;
InterpString(Line);
end
else
InputLoop;
end.
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