feat: add sepby1 combinator

`sepby1` is a common reusable combinator in Haskell Parsec.

This adds `mpc_sepby1(mpc_fold_t f, mpc_parser_t *sep, mpc_parser_t *a)` according to Haskell's implementation:

https://hackage.haskell.org/package/parsec-3.1.16.1/docs/src/Text.Parsec.Combinator.html#sepBy1

Reuses existing `mpc_and`, `mpc_many`, and `mpcf_snd_free`.

Author: steve-chavez

README.md

@@ -356,6 +356,14 @@ Runs `a` one or more times until it fails. Results are combined with fold functi
 
 * * *
 
+```c
+mpc_parser_t *mpc_sepby1(mpc_fold_t f, mpc_parser_t *sep, mpc_parser_t *a);
+```
+
+Runs `a` one or more times, separated by `sep`. Results are combined with fold function `f`.
+
+* * *
+
 ```c
 mpc_parser_t *mpc_count(int n, mpc_fold_t f, mpc_parser_t *a, mpc_dtor_t da);
 ```

mpc.c

@@ -2120,6 +2120,12 @@ mpc_parser_t *mpc_tok_braces(mpc_parser_t *a, mpc_dtor_t ad)   { return mpc_tok_
 mpc_parser_t *mpc_tok_brackets(mpc_parser_t *a, mpc_dtor_t ad) { return mpc_tok_between(a, ad, "{", "}"); }
 mpc_parser_t *mpc_tok_squares(mpc_parser_t *a, mpc_dtor_t ad)  { return mpc_tok_between(a, ad, "[", "]"); }
 
+mpc_parser_t *mpc_sepby1(mpc_fold_t f, mpc_parser_t *sep, mpc_parser_t *a) {
+  return mpc_and(2, f,
+    a, mpc_many(f, mpc_and(2, mpcf_snd_free, sep, mpc_copy(a), free)),
+    free);
+}
+
 /*
 ** Regular Expression Parsers
 */

mpc.h

@@ -220,6 +220,8 @@ mpc_parser_t *mpc_tok_braces(mpc_parser_t *a, mpc_dtor_t ad);
 mpc_parser_t *mpc_tok_brackets(mpc_parser_t *a, mpc_dtor_t ad);
 mpc_parser_t *mpc_tok_squares(mpc_parser_t *a, mpc_dtor_t ad);
 
+mpc_parser_t *mpc_sepby1(mpc_fold_t f, mpc_parser_t *sep, mpc_parser_t *a);
+
 /*
 ** Common Function Parameters
 */

tests/core.c

@@ -242,6 +242,18 @@ void test_eoi(void) {
 
 }
 
+void test_sepby(void) {
+  mpc_parser_t* CommaSepIdent = mpc_sepby1(mpcf_strfold, mpc_char(','), mpc_ident());
+
+  PT_ASSERT(mpc_test_fail(CommaSepIdent, "", "", streq, free, strprint));
+  PT_ASSERT(mpc_test_pass(CommaSepIdent, "one", "one", streq, free, strprint));
+  PT_ASSERT(mpc_test_pass(CommaSepIdent, "one,", "one", streq, free, strprint));
+  PT_ASSERT(mpc_test_pass(CommaSepIdent, "one,two,", "onetwo", streq, free, strprint));
+  PT_ASSERT(mpc_test_pass(CommaSepIdent, "one,two,three", "onetwothree", streq, free, strprint));
+
+  mpc_delete(CommaSepIdent);
+}
+
 void suite_core(void) {
   pt_add_test(test_ident,  "Test Ident",  "Suite Core");
   pt_add_test(test_maths,  "Test Maths",  "Suite Core");
@@ -251,4 +263,5 @@ void suite_core(void) {
   pt_add_test(test_reader, "Test Reader", "Suite Core");
   pt_add_test(test_tokens, "Test Tokens", "Suite Core");
   pt_add_test(test_eoi,    "Test EOI",    "Suite Core");
+  pt_add_test(test_sepby,  "Test SepBy",  "Suite Core");
 }