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/* See LICENSE file for copyright and license details. */
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#if defined(__GNUC__)
# pragma GCC diagnostic ignored "-Wimplicit-fallthrough"
# pragma GCC diagnostic ignored "-Wsuggest-attribute=pure"
#endif
static char **tokens;
static size_t ntokens;
struct node {
int is_operand;
const char *symbol;
struct node *left;
struct node *right;
};
static struct node *
operand_node(const char *token)
{
struct node *ret = malloc(sizeof(*ret));
ret->is_operand = 1;
ret->symbol = token;
ret->left = NULL;
ret->right = NULL;
return ret;
}
static struct node *
operator_node(struct node *left, const char *operator, struct node *right)
{
struct node *ret = malloc(sizeof(*ret));
ret->is_operand = 0;
ret->symbol = operator;
ret->left = left;
ret->right = right;
return ret;
}
static void
print_node(struct node *node)
{
if (node->is_operand) {
printf("%s", node->symbol);
} else {
printf("(");
print_node(node->left);
printf(" %s ", node->symbol);
print_node(node->right);
printf(")");
}
}
static const char *
next_token(void)
{
static size_t token_i = 0;
return token_i == ntokens ? NULL : tokens[token_i++];
}
static struct node *
parse_operand(void)
{
const char *token = next_token();
if (!token)
exit(2); /* syntax error */
return operand_node(token);
}
static int
get_precedence(const char *token, int *ltr)
{
int prec = 0;
*ltr = 1;
if (!strcmp(token, ","))
return prec;
prec++;
*ltr = 0;
if (!strcmp(token, "=") || !strcmp(token, "+=") || !strcmp(token, "-=") || !strcmp(token, "*=") ||
!strcmp(token, "%=") || !strcmp(token, "<<=") || !strcmp(token, ">>=") || !strcmp(token, "&=") ||
!strcmp(token, "^=") || !strcmp(token, "|="))
return prec;
prec++;
*ltr = 1;
if (!strcmp(token, "||"))
return prec;
prec++;
if (!strcmp(token, "&&"))
return prec;
prec++;
if (!strcmp(token, "|"))
return prec;
prec++;
if (!strcmp(token, "^"))
return prec;
prec++;
if (!strcmp(token, "&"))
return prec;
prec++;
if (!strcmp(token, "==") || !strcmp(token, "!="))
return prec;
prec++;
if (!strcmp(token, "<=") || !strcmp(token, "<") || !strcmp(token, ">=") || !strcmp(token, ">"))
return prec;
prec++;
if (!strcmp(token, "<<") || !strcmp(token, ">>"))
return prec;
prec++;
if (!strcmp(token, "+") || !strcmp(token, "-"))
return prec;
prec++;
if (!strcmp(token, "*") || !strcmp(token, "/") || !strcmp(token, "%"))
return prec;
prec++;
*ltr = 0;
if (!strcmp(token, "**"))
return prec;
exit(2);
}
static struct node *
parse_expression_(int min_prec, const char **tokenp)
{
struct node *left, *right;
const char *operator;
int prec, ltr;
left = parse_operand();
*tokenp = next_token();
while (*tokenp) {
prec = get_precedence(*tokenp, <r);
if (ltr ? prec <= min_prec : prec < min_prec)
break;
operator = *tokenp;
*tokenp = NULL;
right = parse_expression_(prec, tokenp);
left = operator_node(left, operator, right);
*tokenp = *tokenp ? *tokenp : next_token();
}
return left;
}
static struct node *
parse_expression(void)
{
return parse_expression_(-1, &(const char *){NULL});
}
int
main(int argc, char *argv[])
{
struct node *node;
tokens = &argv[1];
ntokens = (size_t)argc - 1u;
if (!(node = parse_expression()))
return 1;
print_node(node);
printf("\n");
return 0;
}
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