1 files changed, 219 insertions, 0 deletions
diff --git a/calc1.pas b/calc1.pas
new file mode 100644
index 0000000..0757421
--- /dev/null
+++ b/calc1.pas
@@ -0,0 +1,219 @@
+program calc1;
+
+{$H+}
+
+uses
+    typinfo, sysutils, character;
+
+type
+    TokenType = (TT_Integer, TT_Plus, TT_Minus, 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;
+        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;
+
+function Interpreter.GetNextToken: Token;
+var
+    Text_: String;
+    CurrentChar: Char;
+    Start: Integer;
+
+    procedure SkipWhitespace;
+    begin
+        while (CurPos <= Length(Text)) and IsWhiteSpace(Text[CurPos]) do
+            Inc(CurPos);
+    end;
+
+    function AtEnd: Boolean;
+    begin
+        Result := CurPos > Length(Text);
+    end;
+begin
+    SkipWhitespace;
+
+    if AtEnd then
+    begin
+        Result := TokenEof.Create;
+        Exit;
+    end;
+
+    Start := CurPos;
+
+    while (CurPos <= Length(Text)) and IsDigit(Text[CurPos]) do
+        Inc(CurPos);
+
+    if CurPos - Start > 0 then
+    begin
+        Result := TokenInteger.Create(StrToInt(Copy(Text, Start,
+            CurPos-Start)));
+        Exit;
+    end;
+
+    CurrentChar := Text[CurPos];
+
+    if CurrentChar = '+' then
+    begin
+        Result := TokenPlus.Create;
+        Inc(CurPos);
+        Exit;
+    end
+    else if CurrentChar = '-' then
+    begin
+        Result := TokenMinus.Create;
+        Inc(CurPos);
+        Exit;
+    end;
+
+    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;
+    Eat(TT_Minus);
+
+    Right := Current;
+    Eat(TT_Integer);
+
+    Result := 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.