calc1.pas


1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228

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;
        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);
        Exit;
    end;

    if CurChar = '+' then
    begin
        Result := TokenPlus.Create;
        Inc(CurPos);
        Exit;
    end
    else if CurChar = '-' 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.