From dde78b5d49418989c0a5c6565d75a88d0eb5b87d Mon Sep 17 00:00:00 2001
From: Ryan Brewer <ryanbrew317@gmail.com>
Date: Wed, 31 Jul 2024 16:22:31 +0800
Subject: [PATCH] add stateful combinators

---
 CHANGELOG.md          |  6 ++++++
 gleam.toml            |  2 +-
 src/party.gleam       | 32 ++++++++++++++++++++++++++++++++
 test/party_test.gleam | 17 ++++++++++++++---
 4 files changed, 53 insertions(+), 4 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index a74ffa4..4f17031 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [1.0.3] - 2024-07-31
+
+### Added
+
+ - The `stateful_many` and `stateful_many1` combinators.
+
 ## [1.0.2] - 2024-04-05
 
 ### Added
diff --git a/gleam.toml b/gleam.toml
index 9fb4a23..7d02b10 100644
--- a/gleam.toml
+++ b/gleam.toml
@@ -1,5 +1,5 @@
 name = "party"
-version = "1.0.2"
+version = "1.0.3"
 description = "A little parser combinator library in Gleam."
 
 licences = ["MPL-2.0"]
diff --git a/src/party.gleam b/src/party.gleam
index 3147536..0a09bbf 100644
--- a/src/party.gleam
+++ b/src/party.gleam
@@ -372,3 +372,35 @@ pub fn until(
     },
   )
 }
+
+/// A `many` parser that also gets to update some state with each success
+pub fn stateful_many(state: s, p: Parser(fn(s)->#(a, s), e)) -> Parser(#(List(a), s), e) {
+  Parser(fn(source, pos) {
+    case run(p, source, pos) {
+      Error(_) -> Ok(#(#([], state), source, pos))
+      Ok(#(f, r, pos2)) -> {
+        let #(x, s) = f(state)
+        result.map(run(stateful_many(s, p), r, pos2), fn(res) {
+          let #(#(rest, s2), r2, pos3) = res
+          #(#([x, ..rest], s2), r2, pos3)
+        })
+      }
+    }
+  })
+}
+
+/// A `many1` parser that also gets to update some state with each success
+pub fn stateful_many1(state: s, p: Parser(fn(s)->#(a, s), e)) -> Parser(#(List(a), s), e) {
+  Parser(fn(source, pos) {
+    case run(p, source, pos) {
+      Error(e) -> Error(e)
+      Ok(#(f, r, pos2)) -> {
+        let #(x, s) = f(state)
+        result.map(run(stateful_many(s, p), r, pos2), fn(res) {
+          let #(#(rest, s), r2, pos3) = res
+          #(#([x, ..rest], s), r2, pos3)
+        })
+      }
+    }
+  })
+}
\ No newline at end of file
diff --git a/test/party_test.gleam b/test/party_test.gleam
index aca366b..a5ee7d4 100644
--- a/test/party_test.gleam
+++ b/test/party_test.gleam
@@ -2,12 +2,12 @@
 // License, v. 2.0. If a copy of the MPL was not distributed with this
 // file, You can obtain one at https://mozilla.org/MPL/2.0/.
 
-import gleeunit
-import gleeunit/should
-import party
 import gleam/int
 import gleam/list
 import gleam/string
+import gleeunit
+import gleeunit/should
+import party
 
 pub fn main() {
   gleeunit.main()
@@ -298,3 +298,14 @@ pub fn multiline_comment_test() {
   )
   |> should.equal(Ok("hello! * "))
 }
+
+pub fn stateful_many_test() {
+  let stateful_char = fn(c) {
+    party.char(c)
+    |> party.map(fn(x) { fn(counter) { #(x, counter /. 2.0) } })
+  }
+  party.go(party.stateful_many(100.0, stateful_char("a")), "aaab")
+  |> should.equal(Ok(#(["a", "a", "a"], 12.5)))
+  party.go(party.stateful_many(100.0, stateful_char("b")), "aaab")
+  |> should.equal(Ok(#([], 100.0)))
+}