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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);
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;
Interpreter = class
Text: AnsiString;
CurPos: Integer;
Current: Token;
constructor Create(Text_: AnsiString);
procedure Error;
procedure SkipWhitespace;
function AtEnd: Boolean;
function CurChar: Char;
function GetInteger: Integer;
function GetNextToken: Token;
procedure Eat(T: TokenType);
function Expr: 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 Interpreter.Create(Text_: String);
begin
inherited Create;
Text := Text_;
CurPos := 1;
Current := Default(Token);
end;
procedure Interpreter.Error;
begin
Raise Exception.Create('error!');
end;
procedure Interpreter.SkipWhitespace;
begin
while (not AtEnd) and IsWhiteSpace(CurChar) do
Inc(CurPos);
end;
function Interpreter.AtEnd: Boolean;
begin
Result := CurPos > Length(Text);
end;
function Interpreter.CurChar: Char;
begin
Result := Text[CurPos];
end;
function Interpreter.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 Interpreter.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
Error;
end;
procedure Interpreter.Eat(T: TokenType);
begin
if Current.TokenType = T then
begin
Current := GetNextToken;
end
else
Error;
end;
function Interpreter.Expr: Integer;
var
Left, Op, Right: Token;
begin
Current := GetNextToken;
Left := Current;
Eat(TT_Integer);
Op := Current;
if Op.TokenType = TT_Plus then
Eat(TT_Plus)
else if Op.TokenType = TT_Minus then
Eat(TT_Minus)
else if Op.TokenType = TT_Asterisk then
Eat(TT_Asterisk)
else
Eat(TT_Slash);
Right := Current;
Eat(TT_Integer);
if Op.TokenType = TT_Plus then
Result := TokenInteger(Left).Val + TokenInteger(Right).Val
else if Op.TokenType = TT_Minus then
Result := TokenInteger(Left).Val - TokenInteger(Right).Val
else if Op.TokenType = TT_Asterisk then
Result := TokenInteger(Left).Val * TokenInteger(Right).Val
else
Result := Round(TokenInteger(Left).Val / TokenInteger(Right).Val);
end;
var
Interp: Interpreter;
Line: String;
I: Integer;
procedure InterpString(S: String);
begin
Interp := Interpreter.Create(S);
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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