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#include "parser_internal.h"
typedef struct {
const HParser *p1;
const HParser *p2;
} HTwoParsers;
static HParseResult* parse_butnot(void *env, HParseState *state) {
HTwoParsers *parsers = (HTwoParsers*)env;
// cache the initial state of the input stream
HInputStream start_state = state->input_stream;
HParseResult *r1 = h_do_parse(parsers->p1, state);
// if p1 failed, bail out early
if (NULL == r1) {
return NULL;
}
// cache the state after parse #1, since we might have to back up to it
HInputStream after_p1_state = state->input_stream;
state->input_stream = start_state;
HParseResult *r2 = h_do_parse(parsers->p2, state);
// TODO(mlp): I'm pretty sure the input stream state should be the post-p1 state in all cases
state->input_stream = after_p1_state;
// if p2 failed, restore post-p1 state and bail out early
if (NULL == r2) {
return r1;
}
size_t r1len = token_length(r1);
size_t r2len = token_length(r2);
// if both match but p1's text is shorter than than p2's (or the same length), fail
if (r1len <= r2len) {
return NULL;
} else {
return r1;
}
}
static const HParserVtable butnot_vt = {
.parse = parse_butnot,
};
const HParser* h_butnot(const HParser* p1, const HParser* p2) {
HTwoParsers *env = g_new(HTwoParsers, 1);
env->p1 = p1; env->p2 = p2;
HParser *ret = g_new(HParser, 1);
ret->vtable = &butnot_vt; ret->env = (void*)env;
return ret;
}