From c24e27f0b8b995bd67d9c3b91fdeae077e2b771c Mon Sep 17 00:00:00 2001
From: steve-chavez <stevechavezast@gmail.com>
Date: Tue, 8 Aug 2023 14:15:55 -0500
Subject: [PATCH] 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`.
---
 README.md    |  8 ++++++++
 mpc.c        |  6 ++++++
 mpc.h        |  2 ++
 tests/core.c | 13 +++++++++++++
 4 files changed, 29 insertions(+)

diff --git a/README.md b/README.md
index 6ccc3ef..824aaa2 100644
--- a/README.md
+++ b/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);
 ```
diff --git a/mpc.c b/mpc.c
index c545557..fc560bf 100644
--- a/mpc.c
+++ b/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
 */
diff --git a/mpc.h b/mpc.h
index 545b35e..49a08ee 100644
--- a/mpc.h
+++ b/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
 */
diff --git a/tests/core.c b/tests/core.c
index 52463e1..35e1411 100644
--- a/tests/core.c
+++ b/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");
 }