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/*
An example of parsing in plain C, without memory allocations, and
with adjustable maximum parsing depths for literals and trees.
An example:
cc example.c && ./a.out 1 0 'a b() (c\ d\(\) (e (f)))'
*/
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int is_space (char c) {
return (c == ' ' || c == '\n');
}
ssize_t read_token (const char *input, size_t input_len, int delimited) {
size_t i;
/* A tree: match until it is closed */
if (input[0] == '(') {
int level = 0;
for (i = 0; i < input_len; i++) {
if (input[i] == '(') {
level++;
} else if (input[i] == ')') {
level--;
} else if (input[i] == '\\') {
i++;
}
if (level == 0) {
return i + 1;
}
}
return -1;
}
/* A literal */
for (i = 0; i < input_len; i++) {
if ((! is_space(input[0])) && input[i] == '\\') {
i++;
continue;
}
if (delimited &&
(is_space(input[0]) ^ is_space(input[i]))) {
return i;
}
if (input[i] == '(' || input[i] == ')') {
return i;
}
}
return i;
}
size_t unescape (const char *src, size_t src_len, char *dst) {
size_t i, j;
for (i = 0, j = 0; i < src_len; i++, j++) {
if (src[i] == '\\') {
i++;
}
dst[j] = src[i];
}
return j;
}
int main (int argc, char **argv) {
int max_depth_tree = atoi(argv[1]);
int max_depth_literal = atoi(argv[2]);
char *input = argv[3];
if (argc != 4) {
printf("Usage: %s <max_deptH_tree> <max_depth_literal> <input>\n",
argv[0]);
return -1;
}
ssize_t input_len = strlen(input);
int level = 0, pos = 0;
while (pos < input_len) {
if (input[pos] == ')') {
if (level > 0) {
level--;
} else {
puts("Parentheses closed unexpectedly");
return -1;
}
pos++;
continue;
}
ssize_t token_len = read_token(input + pos, input_len - pos,
level < max_depth_literal);
if (token_len <= 0) {
return -1;
}
size_t unescaped_len = token_len;
if (input[pos] != '(') {
unescaped_len = unescape(input + pos, token_len, input + pos);
}
printf("%d %ld %ld: ", level, token_len, unescaped_len);
fwrite(input + pos, 1, unescaped_len, stdout);
puts("");
if (input[pos] == '(' && level < max_depth_tree) {
level++;
pos++;
} else {
pos += token_len;
}
}
}
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