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