/
interpreter.c
167 lines (142 loc) · 2.39 KB
/
interpreter.c
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
/* TODO:
- Handle identifiers other than x and y. Q: These will be user-set
parameters. How will they set it?
- Avoid reading the string at each run? How?
- Handle trig. functions
*/
float expression();
void skip_white();
static char tmp[32];
static char *look;
struct {
float x,y;
} env;
void get_char() {
look++;
}
void abort() {
exit(1);
}
void expected(char *s) {
printf("%s expected\n", s);
abort();
}
void match(char x) {
if (*look == x) {
get_char();
skip_white();
}
else {
snprintf(tmp, 32, "%c", x);
expected(tmp);
}
}
bool is_alpha(char c) {
if ((c >= 'a' && c <= 'z') ||
(c >= 'A' && c <= 'Z'))
return true;
else
return false;
}
bool is_digit(char c) {
if (c >= '0' && c <= '9')
return true;
return false;
}
bool is_white(char c) {
return (c == ' ');
}
void skip_white() {
while (is_white(*look))
get_char();
}
bool is_addop(char c) {
if (c == '+' || c == '-')
return true;
return false;
}
float get_num() {
if (!(is_digit(*look) || *look == '-')) {
expected("float");
}
char buf[16];
int i = 0;
while (is_digit(*look) || *look == '.') {
buf[i++] = *look;
get_char();
}
buf[i] = 0;
skip_white();
float ret = atof(buf);
return ret;
}
char get_name() {
if (!is_alpha(*look))
expected("name");
char ret = *look;
get_char();
skip_white();
return ret;
}
float factor() {
float value;
float sign = 1.0;
if (*look == '-') {
sign = -1;
}
if (*look == '(') {
match('(');
value = expression();
match(')');
return value;
}
else if (is_alpha(*look)) {
switch (*look) {
case 'x': {
value = env.x;
} break;
case 'y': {
value = env.y;
} break;
}
get_char();
skip_white();
}
else {
value = get_num();
}
return sign*value;
}
float term() {
float value = factor();
while ((*look == '*') || (*look == '/')) {
switch (*look) {
case '*': {
match('*');
value = value * factor();
} break;
case '/': {
match('/');
value = value / factor();
} break;
}
}
return value;
}
float expression() {
float value;
value = term();
while (is_addop(*look)) {
switch(*look) {
case '+': {
match('+');
value = value + term();
} break;
case '-': {
match('-');
value = value - term();
} break;
}
}
return value;
}