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Add optional form to peg (shorthand for (between 0 1 patt)).

This commit is contained in:
Calvin Rose 2019-01-15 14:08:03 -05:00
parent f0fcdf6bc5
commit 4eeadd7463
3 changed files with 20 additions and 1 deletions
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2
doc/Peg.md
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@ -109,6 +109,8 @@ can be thought of as the looping and branching forms in a traditional language
| `(! patt)` | Alias for `(not patt)` |
| `(look offset patt)` | Matches only if patt matches at a fixed offset. offset can be any integer. patt will not produce captures and the peg will not advance any characters. |
| `(> offset patt)` | Alias for `(look offset patt)` |
| `(opt patt)` | Alias for `(between 0 1 patt)` |
| `(? patt)` | Alias for `(between 0 1 patt)` |
PEGs try to match an input text with a pattern in a greedy manner.
This means that if a rule fails to match, that rule will fail and not try again. The only

10
src/core/peg.c
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@ -713,7 +713,6 @@ static void spec_replace(Builder *b, int32_t argc, const Janet *argv) {
emit_2(r, RULE_REPLACE, subrule, constant);
}
/* For some and any, really just short-hand for (^ rule n) */
static void spec_repeater(Builder *b, int32_t argc, const Janet *argv, int32_t min) {
peg_fixarity(b, argc, 1);
Reserve r = reserve(b, 4);
@ -744,6 +743,13 @@ static void spec_atmost(Builder *b, int32_t argc, const Janet *argv) {
emit_3(r, RULE_BETWEEN, 0, n, subrule);
}
static void spec_opt(Builder *b, int32_t argc, const Janet *argv) {
peg_fixarity(b, argc, 1);
Reserve r = reserve(b, 4);
uint32_t subrule = compile1(b, argv[0]);
emit_3(r, RULE_BETWEEN, 0, 1, subrule);
}
static void spec_matchtime(Builder *b, int32_t argc, const Janet *argv) {
peg_fixarity(b, argc, 2);
Reserve r = reserve(b, 3);
@ -773,6 +779,7 @@ static const SpecialPair specials[] = {
{"/", spec_replace},
{"<-", spec_capture},
{">", spec_look},
{"?", spec_opt},
{"any", spec_any},
{"argument", spec_argument},
{"at-least", spec_atleast},
@ -788,6 +795,7 @@ static const SpecialPair specials[] = {
{"if-not", spec_ifnot},
{"look", spec_look},
{"not", spec_not},
{"opt", spec_opt},
{"position", spec_position},
{"range", spec_range},
{"replace", spec_replace},

9
test/suite3.janet
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@ -319,4 +319,13 @@
(check-match janet-longstring "``` `` ```" true)
(check-match janet-longstring "`` ```" false)
# Optional
(check-match '(* (opt "hi") -1) "" true)
(check-match '(* (opt "hi") -1) "hi" true)
(check-match '(* (opt "hi") -1) "no" false)
(check-match '(* (? "hi") -1) "" true)
(check-match '(* (? "hi") -1) "hi" true)
(check-match '(* (? "hi") -1) "no" false)
(end-suite)