From d7c26e5858240a101085c1e8a1ce13928a39b112 Mon Sep 17 00:00:00 2001
From: Robert Bendun <rob.bendun@gmail.com>
Date: Fri, 30 Dec 2022 15:30:50 +0100
Subject: [PATCH] digits builtin

---
 CHANGELOG.md                             |  1 +
 musique/interpreter/builtin_functions.cc | 57 ++++++++++++++++++++++++
 regression-tests/builtin/digits.mq       |  8 ++++
 regression-tests/test_db.json            | 18 +++++++-
 4 files changed, 83 insertions(+), 1 deletion(-)
 create mode 100644 regression-tests/builtin/digits.mq

diff --git a/CHANGELOG.md b/CHANGELOG.md
index e8bc40e..d64d89e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Printing version number on non-quiet launch, or when provided `--version` or `:version`
 - Builtin function documentation generation from C++ Musique implementation source code
+- New builtins: digits
 
 ### Removed
 
diff --git a/musique/interpreter/builtin_functions.cc b/musique/interpreter/builtin_functions.cc
index c5b78b6..e81102b 100644
--- a/musique/interpreter/builtin_functions.cc
+++ b/musique/interpreter/builtin_functions.cc
@@ -1147,6 +1147,62 @@ static Result<Value> builtin_mix(Interpreter &i, std::vector<Value> args)
 	return result;
 }
 
+inline void append_digits(std::vector<uint8_t> &digits, usize base, Number number)
+{
+	auto start = digits.size();
+
+	number.simplify_inplace();
+
+	auto integer_part = number.num / number.den;
+	number.num -= integer_part * number.den;
+
+	do {
+		digits.push_back(integer_part % base);
+		integer_part /= base;
+	} while (integer_part != 0);
+	std::reverse(digits.begin() + start, digits.end());
+
+	if (number.den != 1) {
+		std::unordered_set<Number> repeats;
+
+		do {
+			repeats.insert(number);
+			number.num *= base;
+
+			auto const digit = number.floor().as_int();
+			digits.push_back(digit);
+
+			number.num = number.num - digit * number.den;
+			number.simplify_inplace();
+		} while (number.num != 0 && !repeats.contains(number));
+	}
+}
+
+/// Converts number to array of its digits
+static Result<Value> builtin_digits(Interpreter &interpreter, std::vector<Value> args)
+{
+	// For now it's a constant. It waits on some kind of keyword parameters
+	// so base can be provided nicely
+	auto const base = 10;
+
+	std::vector<uint8_t> digits;
+
+	auto args_flattened = Try(deep_flat(interpreter, args));
+	for (auto const& arg : args_flattened) {
+		if (auto num = get_if<Number>(arg)) {
+			append_digits(digits, base, *num);
+		} else {
+			// TODO This may be an error. Currently we fail silently
+			continue;
+		}
+	}
+
+	std::vector<Value> result;
+	result.reserve(digits.size());
+	std::transform(digits.begin(), digits.end(), std::back_inserter(result), [](auto digit) { return Number(digit); });
+	return result;
+}
+
 /// Call operator. Calls first argument with remaining arguments
 static Result<Value> builtin_call(Interpreter &i, std::vector<Value> args)
 {
@@ -1175,6 +1231,7 @@ void Interpreter::register_builtin_functions()
 	global.force_define("call",           builtin_call);
 	global.force_define("ceil",           builtin_ceil);
 	global.force_define("chord",          builtin_chord);
+	global.force_define("digits",         builtin_digits);
 	global.force_define("down",           builtin_down);
 	global.force_define("duration",       builtin_duration);
 	global.force_define("flat",           builtin_flat);
diff --git a/regression-tests/builtin/digits.mq b/regression-tests/builtin/digits.mq
new file mode 100644
index 0000000..044a033
--- /dev/null
+++ b/regression-tests/builtin/digits.mq
@@ -0,0 +1,8 @@
+say (digits 3456),
+say (digits (100/10)),
+say (digits 0),
+say (digits (0 - 1234)),
+say (digits 0 0 0 0),
+say (digits (4/3)),
+say (digits 0.5),
+say (digits 1234.5678),
diff --git a/regression-tests/test_db.json b/regression-tests/test_db.json
index 89e6fd7..000767b 100644
--- a/regression-tests/test_db.json
+++ b/regression-tests/test_db.json
@@ -200,7 +200,23 @@
           "10"
         ],
         "stderr_lines": []
+      },
+      {
+        "name": "digits.mq",
+        "exit_code": 0,
+        "stdin_lines": [],
+        "stdout_lines": [
+          "(3, 4, 5, 6)",
+          "(1, 0)",
+          "(0)",
+          "(1, 8, 4, 4, 6, 7, 4, 4, 0, 7, 3, 7, 0, 9, 5, 5, 0, 3, 8, 2)",
+          "(0, 0, 0, 0)",
+          "(1, 3)",
+          "(0, 5)",
+          "(1, 2, 3, 4, 5, 6, 7, 8)"
+        ],
+        "stderr_lines": []
       }
     ]
   }
-]
+]
\ No newline at end of file